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> I also have it so the heating turns off when I go into town and turns back on when I'm just a few train stops away so my place is nice and toasty for me getting home!
If your goal is saving energy/money, you don’t want a system capable of going from cool to toasty in 20 minutes.
Instead, you want a system that runs (much) lower water circulation temperatures (giving lower losses in the unconditioned spaces and more even room heating). That can be done to any condensing boiler by just turning down the flow target temperature.
A second layer of optimization on top of this is the addition of outdoor reset/weather compensation which will adjust that flow temperature based on the outside temperature, giving a flow temperature than can just barely restore the building to the desired setpoint temp.
With mine properly tuned, I was targeting having the thermostat act more like a high-limit and for it to call for heat between 22 and 24 hours per day while not overheating the house. That often meant flow temps in the 110°F (warm day) to 135°F (below freezing day) range. Compared to the prior winter (at a constant 160°F flow), the house used 8-15% less gas and was wildly more comfortable. (This setup does preclude using deep setback settings, which also can save money, because recovery times are necessarily long in such a scheme, unless you have an even smarter control system that can run perfectly tuned water most times but hotter water during recovery from setbacks.)
That’s an artifact of how heating is setup inside your home. Which is more efficient depends on where you’re dumping heat inside the home, levels of insulation, etc.
Energy moves from hot to cold linearly with temperature differences. Hypothetically, if the pipe was the same temperatures as the inside of your home all the heat transferred would be outside the envelope. The hotter the pipe the better this ratio becomes. This is true regardless of what percentage of the pipe is inside the envelope.
However, heating along the exterior of the home under windows and such then you’ll heat the exterior walls to higher temperatures than the interior thermostat thus losing more heat to the outside. Radiant heating on the other hand largely avoids this effect.
Look at ISO 7730, a lot of comfort comes from non-cold walls and their radiant heat and small difference of wall temperatures to air temperatures. So having a thoroughly heated home allows you to lower your air temperature. Apart from that modern gas and even more heat pumps greatly gain efficiency by lowering flow water temperatures.
Having read that document, the ISO 7730 model itself depends on stable temperatures. However, I think the key is simply to understand thermal mass; people can be in hotter air, but feel cold due to cold surfaces (e.g., floors or furniture), which heat more slowly (or lose heat more slowly) than the air itself.
Therefore, 1st: Heating/cooling cycles from your HVAC are fighting these objects because they don't mix at the same speed as other objects (e.g., the air itself), so you end up with gradients across objects; people rate this feels unpleasant.
2nd: Mechanical equipment tends to operate more efficiently under constant load compared to constant start and stop cycles.
With #1 and #2, you can just heat constantly to increase both the uniformity of heating across objects and also the efficiency of the mechanical equipment's energy conversion.
There's a 3rd point, which, really, is just a sneaky way of reframing #1 and #2, and that is that you can also lower your setpoint and still have a subjectively superior comfort perception compared to a cyclic system. It drives home the point to say "constant 68F feels more comfortable than intermittent 72F." But it also invites the complaint about constant versus intermittent energy use, right? So I think just detailing #1 and #2 is better.
That spec aligns with my understanding, including the model's dependence on comfort perception. I was, initially, in disbelief about it, but changed my mind after reading thru. The texty reply was to make it more palatable for someone like me to accept. I think we agree.
One thing I missed in summary is the concept of general radiant temperature gradient. It's not only about the gradient for conduction, but for radiation (and convection). So you could probably improve my summary by talking about any gradient between different objects in the environment and their EM, which feels unpleasant (but I think it had value in its reduction of the problem, too).
It’s a deep rabbit hole as condensation, humidity, etc also enter the picture. Efficiently lowering temperatures for sleeping further complicates things.
That said, heat loss is through exterior surfaces so you really want to avoid spot heating of poorly insulated exterior walls. Thus the design of baseboard heaters can make a larger impact than you’d think.
Baseboard heaters need very high temperatures. I would not recommend installing this anywhere. Having big Typ 33 heaters for temperatures below 45°C will greatly increase efficiency of your heating system. Otherwise, a split air con is also an efficient way of heating.
Baseboard heaters are often sized such that very high temps are needed (because that's what cheapest/lowest labor/least space used), but they don't have to be sized that way. In the attic bedroom, we have baseboards around the entire perimeter on two walls and same in the bath. I run the attic zone on the same water temp (outdoor reset controlled to be quite low) as the rest of the house (mostly large cast iron rads, one cast iron convector). Good insulation and air sealing in the attic means that the attic zone calls way less than the downstairs.
Which is not exactly efficient. 40C or less is desirable.
My return water temps are 115F (46C) on a P98 design heating day, and obviously cooler on warmer than design days. Cooler is always better, but "baseboards require 180F [82C] water because that's what's on the spec sheet" is a commonly-held but mistaken belief.
This is bad. Return water should be less 35 degree max. Actually 30 degree after the heat pump would be ideal: https://www.flow30.de/
[citation needed]
Ah this is school knowledge of thermodynamics: the smaller the delta the more efficient the heat pump. For human comfort look at the iso7730. Also the system is self regulatory with such low temps.
Heat pumps and furnaces behave very differently here.
For a furnace you’re talking fractions of a percent difference in efficiency across a wide temperature range so by far the most critical issue is total heat losses to the outside. A heat pump’s efficiency is far more variable making total losses to the outside less important.
First, sooner or later you have to replace your furnace with a heat pump. Second, modern furnaceses are condensing. Return temp should be as low as possible maximise condensing.
We agree return temps should be lower, but to determine how critical this is you need to out numbers on that. In steady state operation at maximum load a difference in return temperatures of 15f is ~1% efficiency. But steady state at maximum load is an extreme situation the average return temperature is well below that theoretical maximum thus an even wider difference is needed for a seasonal difference of 1%.
Redundancy is critical in areas that get really cold. That may eventually mean turning to hydrogen, but a backup gas furnace for a well insulated home really isn’t a major CO2 contributor. More relevant to the discussion it further reduces the impact of minor changes in efficiency or comfort.
As said, at some point you will likely replace your furnace by a heat pump. Then all investment to low temperatures will pay off. A modern gas furnace is no backup for a heat pump, as it also needs electricity. I would recommend a low tech solution like a wood stove for backup. I have one in my cellar. In case of a long power outage I would likely just install this through some open window and do some redneck stuff to make it airtight.
Backup doesn't necessarily mean "in case of grid failure". A gas boiler or a simple electric boiler is a valid backup to a heat pump being inoperative, in the middle of defrost cycle, or otherwise just unable to provide enough BTU/hr into the building due to an extreme cold temperature.
Particularly in temperatures where the heat pump is at/under 2.0 COP for a few dozen hours per year, an electric boiler makes a great deal of sense. It's almost as clean as the heat pump in the extremely rare times when it's needed for supplementation due to extreme cold temps, can allow for a more suitably sized heat pump to cover the 99% of heating hours [meaning greater efficiency there], is extremely reliable due to its simplicity, is fully automatable with existing controls, doesn't require local gas supply network, and is a pretty good match for a heat pump.
Trusting in the power grid for both is obviously not redundant, but it’s cheaper to get independent power for a furnace than heat pumps. Actual redundancy means you want completely independent systems so you shouldn’t then use the same heat delivery loops/pumps/fans either.
Wood stoves require you to physically be home and are kind of a pain to use thus make a poor backup on their own, though a solid 2nd backup.
PS: Most areas are better off with solar thermal + heat pumps. Solar thermal however requires sunlight which not everyone gets in the depth of winter.
I moved all my radiators away from under windows (and upgraded the windows to triple glazing) to avoid maximising the temperature differential and energy loss through the wall under the windows, while eliminating the cool drafts that the under-window radiator placement was intended to counter.
Radiators were originally designed to heat more than needed, so you could open the windows.
In New York, at least - the standards were never changed to accomodate for closed windows in 1920. Snopes has a rundown. https://www.snopes.com/fact-check/apartment-radiator-pandemi...
My house (built in 1916) was insanely over-provisioned. When we upgraded to a modulating-condensing boiler, we halved the BTUs and are still able to easily keep the house heated to any desired temperature even on the coldest winter days.
Do you mean you moved them to another wall, or just increased the gap?
(not a native speaker here)
Moved them to another wall.
Eg: https://www.earth.org.uk/note-on-superinsulating-bedroom.htm...
What do you do for ventilation?
The windows all still open, but in winter we have (nearly) enough MHRV (Mechanical Heat Recovery Ventilation) not to need to ventilate directly, eg see:
https://www.earth.org.uk/MHRV-mechanical-heat-recovery-venti...
I'm really confused about (not complaining, just not understanding) the downvotes.
These are statements of neutral fact, and the whole process is described in some detail on my site, for each room that we retrofitted.
I don't understand if I have caused offense or something: apologies if somehow so!
I'm not sure, but I think that the reason that radiators are placed near windows (at least historically) was to avoid hot/cold spots in rooms.
By placing the radiator near the place that is likely the coldest place in the room, you ensure that the room is an even in temperature as possible. Rather than to counteract 'cool draughts'. I think.
So perhaps people thought that your initial comment was wrong/misleading.
But if you have triple glazing and this mitigates the heat loss, then the coldest wall of your room may no longer be the one with a window, so you may well be doing the right thing for your room(s).
Even if the coldest wall is still the exterior one (it should be, thermodynamically), best maintaining comfort in the room need no longer be by pumping heat out through that wall (or window) to reduce thermal gradients in the rest of the room. Those residual gradients (and, eg, cold drafts down those cooler exterior walls) can be small enough to not need fixing any more.
Agree, switching on and off is the worst way of heating. If you look into ISO 7730, then a lot of comfort comes from non cold walls: https://de.wikipedia.org/wiki/ISO_7730 This means that in a reasonable insulated home, your best bet for comfort is to just keep the temperature constant and low like 20°C. This also allows you to lower your water temperatures which improves efficiency of your heat pump or boiler.
Depending on the region, "reasonably insulated home" really is the factor that makes this not so viable for a lot of people. In my Mediterranean-adjacent climate country, most homes are just not well insulated at all, and having heat running 24/7 during winter is extremely costly and inefficient even if the heating is on a low setting.
These home will most likely have a split air con, which will be the most efficient way of heating them. Also there is so much other room for improvement like drafty windows and doors etc.
In many warmer climates, the mini split air conditioners sold are cooling capability only. This is much cheaper to purchase for a 12,000 up to 24,000 btu/h unit than one which is also capable of heating the interior.
Not true, I can buy a Chinese 4kw Model for 650€ which can heat till -15degree. Doubt that you can save much.
Go price air conditioners in the uae or Kuwait or similar, the cooling only models are very much a thing that exists on the market.
But not in Europe. It is only one 4 way valve extra to enable heating.
Yes!
I used to divide my time between a concrete hulk of a NYC apartment building, and a California home insulated to notoriously poor California standards. I was plenty warm in New York winters just from my neighbors' heat nearly all of the time. In California, there was a narrow window (think "Apollo 13 re-entry") between too cold and too warm.
Then we modernized ceiling fans, and I hit on running them in "winter mode" drawing hot air up to flow back down the walls. Bingo! I love that ISO 7730 confirms this.
I've read that it's always more efficient to turn heating off when you're not home and then turn it back on when you return. Is the reason for it being on 22-24 hours here that it takes a very long time to get back to the desired temperature, meaning you'd actually be cold for quite a while as it returned to the desired temperature?
The hidden factor here is that condensing boilers and heat pumps have non-linear efficiency vs flow temperature curves. Heat pumps in particular show high increase in coefficient of performance (CoP) as flow temperature drops.
The other variable is how well controlled your heating is. A lower flow temperature means less overshoot of the target set point - and as losses scale linearly with temperature delta, that can mean higher energy losses (depending on the characteristics of the controller of course).
Whether or not you care about losses in unheated spaces depends on your system topology. Personally, all my heating pipes are within the thermal envelope of my house, so flow temperature has no bearing on those losses at all.
If you had a resistive electric boiler, flow temperature would have absolutely no effect on efficiency. You'd be completely right, that running heating only when you needed it would be more energy efficient.
You missing ISO7730, it is a system for humans and not air temperature control. (tl;dr heating your home 24/7 allows you to lower air temperature for the same comfort. )
Thanks for the explanation.
> I've read that it's always more efficient to turn heating off when you're not home and then turn it back on when you return.
50 years ago this was _always_ the case, but condensing boilers and especially heat pumps muddy the waters a little. Condensing boilers can be close to 100% efficient (vs ~70-80% for ye olde gas boilers), but generally only at a fairly specific operating temperature, which may be lower than you'd need to get a rapid rise in temperature. Heatpumps are >100% efficient (that is for every joule of electricity you put in they move more than one joule), but are even more fussy about operating temperature.
The answer now is going to be a solid 'it depends', based on behaviour of the heating system, outside temp, desired inside temp, insulation...
> Condensing boilers can be close to 100% efficient (vs ~70-80% for ye olde gas boilers)
So you save up to 30% of the gas while heating your home nearly 24 hours a day, instead of saving 67% of the gas by using it only for the ~8 hours that you're home and not under a duvet?
The math might work out for those who work from home, but I mean in the standard case with an hour's commute (round-trip), an 8-hour work day, and a 30-minute lunch break (9.5h gone, 7h sleep -> 7.5h during which the apartment should be warm if you run no errands). Of course, you'd schedule it to start before you get home, but it can also stop a bit before going to bed
I've been hearing both arguments for years and while it's exceedingly convenient to believe the condensing boiler story and just heat 24/7 to always come home in luxurious warmth, nobody ever does the math. You're one of the few people who even mention what the alleged savings are in the first place
We have a condensing boiler, chosen by my landlord so I'm no expert but I looked into it because we pay the bills in the end. The device's manual lists the efficiency as 88% ƞ4 at 60°C return water temperature, called high-temperature operation, and 98% ƞ4 at 30°C return temperature. It also gets tested yearly by a professional (Schornsteinfeger I think they call it here) and produces two efficiency measurements. Just looked up the record again: the mechanic handwrote "min" and "max" with them, so I presume that the "max" one is where the system operates at maximum capacity (minimum efficiency, then?), where the efficiency is 98%. At the "min" setting, the efficiency is shown as 106% (iirc some older measurement techniques don't include the condensation efficiency gain in the percentage, that's how it goes above 100%, or so I read when I looked it up a few years ago). For that difference, please correct me if I'm overlooking something but using a low heat for 24h/day makes no mathematical sense to me
Yeah, this only works with quite well-insulated houses, where they're very little heat loss (the system will then spend most of its time off _anyway_, as it has reached desired temperature).
ISO 7730 to the help. Just keep low overall temperatures and heat 24/7 in a reasonably insulated home.
I work entirely remote so, other than travel, there are not many long periods when the house is unoccupied.
I target the long run time to maximize efficiency. A 160°F pipe will lose more heat to the part of the building that I don’t want to heat as well as more heat to the wall right behind the radiators. It also results in the house going micro too-hot, too-cold, too-hot, too-cold as it cycles. Mine is constantly trickling in just enough heat to replace the heat lost instead of cycling between adding way more than needed then none for a while.
Another large effect is that low return water temperatures into the boiler allow for greater condensation of exhaust gas energy to be used in the building instead of sent outside. Walking by my house on a cold day, you’ll see minimal steam plume during operation. All that steam I see my neighbors emitting is energy they paid for and delivered to the outside… (They paid a lot for a boiler with a 95% or 98% sticker and run it at 80% efficiency.)
https://kw-engineering.com/how-to-optimize-condensing-boiler...
> Another large effect is that low return water temperatures into the boiler allow for greater condensation of exhaust gas energy to be used in the building instead of sent outside.
Correct.
> Walking by my house on a cold day, you’ll see minimal steam plume during operation. All that steam I see my neighbors emitting is energy they paid for and delivered to the outside… (They paid a lot for a boiler with a 95% or 98% sticker and run it at 80% efficiency.)
Please check your assumptions.
A boiler operating in condensing mode will produce a trickle of liquid condensate (that may well be drained somewhere that you can’t see [0]), teeny tiny drops of condensate suspended in gas (colloquially “steam”, but it’s more like fog), and some residual water vapor mixed with the exhaust gasses. You can see the “steam”, but you cannot see that residual vapor except to the extent that it condenses further as the exhaust stream cools after it exits, much as you can see some of your own exhaled water vapor on a cold day as it condenses outside your nose or mouth. The exhaust gas is saturated: it has maximum humidity and is at its own dewpoint, so there is a lot of visible fog. The droplets that form inside the boiler and escape with the flue gas do not represent wasted heat: their heat of fusion has been captured.
A boiler operating in non-condensing mode will produce no liquid condensate, and its exhaust will be well above its own dewpoint. It will contain far more water vapor than a condensing boiler, but you cannot see that vapor except insofar as the flue gas has a different index of refraction than the surrounding air and distorts the background a bit. Depending on weather, a bit of it may condense later. All of it is wasted energy.
[0] This liquid condensate is nasty stuff: it’s basically carbonated distilled water plus some impurities but not usefully buffered, and it’s rather acidic. It will quickly corrode many metals, including copper and many common copper alloys, non-stainless steel, galvanized steel, etc. Non-condensing furnaces and boilers are generally carefully engineered to avoid condensation, because the condensation would damage them. If your plumber is unaware of the degree to which boiler condensate is corrosive and uses copper pipes or metallic fittings (push-to-fit in the style commonly sold as “Sharkbite”), the system will fail. Use plastic pipes (PVC or PEX) and plastic (or maybe stainless steel) fittings such as ordinary solvent-cement PVC fittings, “engineered plastic” PEX fittings, or push-to-connect fittings with plastic wetted surfaces. John Guest makes these, and there is also the somewhat bizarre ProLock brand, which seems to be some sort of joint offering from John Guest and Sharkbite.
I’m imagining that what I see in my neighbor’s exhaust is the subsequent condensation as their exhaust gas cools to where the dew point is met and visible moisture becomes apparent.
I can see a clear difference between running my own boiler at 25°F OAT (lots of “steam”) versus 40°F OAT (almost none) while I see my cross-street neighbor showing large plumes on both. I’m not sure if I mistyped above or I’m actually thinking about it wrong, but I don’t think my observations are incorrect.
Having that water condense outside the building (giving up heat to the neighborhood) is less efficient than having that water give up its heat into the incoming (return) water.
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> A 160°F pipe will lose more heat to the part of the building that I don’t want to heat as well as more heat to the wall right behind the radiators.
You’ve got the first part of that backwards, it’s the walls near your radiators that are your problem and need more insulation.
Indeed the building is 100 years old and impractical to retrofit insulation in any cost-efficient way (structural brick, lathe and plaster walls with about 1” of air space in the original parts of the building).
Btw, a heated blanket would be a lot more efficient, as it warms just your butt.
Heated blankets are ok, but you have to arrange them just so, and then you can’t move without fussing with the cord. It’s the last resort after layering warm clothes before bumping up the thermostat.
I use a heated blanket as a bottom layer sometimes. Lets you move around and do whatever you want with the blanket fixed in place and the cord not in the way. I have larger heated blanket that has independent power/settings for each half. I turn one half on max and leave the other off and can roll and find the perfect direct heat and if using another regular blanket on top all that is captured too.
Thanks for the explanation.
Unsure if what you posted is true because I don’t know about water based systems, however this has been proven false for heat pumps.
Specifically, setting a fixed temp vs turning things up/down/off when you are leaving and reversing it before you get home. There was little difference either way. The amount of electricity consumed was similar to both.
I wish I had a link, they even tested cases where efficiency was lost heating things up. This includes “emergency heating”.
> If your goal is saving energy/money, you don’t want a system capable of going from cool to toasty in 20 minutes.
Depends. As explained in a sibling comments, I have some rooms that have combined UFH and radiators, and if the desired temp is more than 1 celsius away from the current temp, then both are driven, otherwise it's just the UFH.
Indeed “depends” is almost always the answer.
So long as you can get the boiler return water temps low enough, you can operate the boiler in its high efficiency range.
Most dual-temp setups are set for the highest temp and mixed-down to provide the lower temp for under-floor. That’s cheapest in terms of equipment and install but cannot be as efficient as a system that mixes down when both loads call but also lowers flow temp (thereby lowering return temp) when no high-temp rads are calling.
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Capable doesn't mean it always puts out that amount of heat.
A well-designed system would have good insulation, can dump 10000W watts of heat out and bring the room from cool to toasty in 5 minutes, and then scale back and maintain the temperature after that by putting out 500W after that.
This also tends to be more efficient in practice because if you know it only takes 5 minutes to heat up you are less likely to want to leave it on when you're not around.
But it can't heat up the walls and other surfaces in that amount of time. The building will feel colder for the same air temperature setting until those objects have had time to warm up as well.
This is a great post which describes how most commercial boilers are controlled. I’m looking at a sequence of operations for a boiler project I did recently and the hot water supply setpoint for -20F outdoor air is 145F and for +45F the hot water supply setpoint is 120F.
Most home boilers lack an outdoor air reference temp sensor but all commercial boilers have them.
Also, condensing boilers are amazing, the size difference alone vs an old tube boiler is wild, very small in comparison.
It's an awesome hack!
It seems like the easier hack would be to put a peltier heater/cooler under the thermostat then control that remotely to assume control over what temperature the thermostat sees.
The link to the exact model of thermostat isn't working, so I don't know how amenable its design is to this approach, but the thermostats I've used are generally wall-mounted and putting a heat/cool source under them wouldn't be too hard. You'd need to make sure that you didn't send both the heat and cool into the thermostat, but that's a simple positioning problem.
Cool idea! It's ironic that this is such an efficient use case for device that is so inefficient.
Actually the best control system for such a boiler would be to control the heating curve where heating water temperature is fixed to the outside temperature. If you aim for the lowest water temperatures possible, then the system will become quite slow reacting. Then you only need to adjust the flow of water to the individual rooms to fix varying temperature issue. But this is long term manual optimization process which takes 1 to 2 years to perfect.
yeah i put mine in the freezer
I wonder what the ideal one-size fits all thermostat looks like.
The one in my apartment has a “feature” a lot of US thermostats now have, where you set four ordered times called wake, leave, return, and sleep and the temperature you want the space in each interval. I know very few people who actually live in a household where everyone wakes, leaves, returns, and sleeps on the same schedule every day.
I work from home and personally just want to set a temperature and have the space stay at that temperature indefinitely but this system requires that I tap through and enter the desired temperature four times, while confirming the four intervals.
I guess I’d be happier with a more programmable thermostat that I could set to behave like an old school dial thermostat.
I'm still of the opinion that a dial works best. Especially in modern homes (in Europe at least), there seems to be a school of thought that you should just leave your thermostat at the same temperature at all times - the theory being that warming up a cold house in the morning costs more energy than maintaining a stable temperature.
Anyway, my ideal setup would be to install 'smart' thermostat taps on every radiator in the house, either manually turn them down when you're not in the room or have them automatically detect activity or open windows and adjust accordingly. But each one has the authority to trigger the central boiler if needs be, instead of only the master thermostat in the living room.
> the theory being that warming up a cold house in the morning costs more energy than maintaining a stable temperature
This is only true if the heating happens quickly and the system is less efficient when heating quickly. Otherwise, this doesn't make sense from a physics standpoint. A temporarily lower temperature differential means less kWh of heat lost.
This is a whole research topic, my PhD in fact!
FWIW I run my heat pump intermittently and with locally-smart TRVs that get to call for heat centrally, and a weather compensation only flow temperature curve, and it WORKSFORME!
Fascinating read.
Certainly feels like I'd need PhD from it to successfully install, modify, calibrate and run the installation until its fully adjusted, for the peak comfort and minimum cost/dirty energy use.
I enjoyed reading this, thank you.
\o/
I think that maintaining a stable temperature means warm walls/floors/furniture and potentially cooler air temperature, as opposed to a cold house with intermittently warm air. Most people can feel comfortable at a lower thermostat (air) temperature if the walls etc are warm due to maintaining a stable temperature. I don't have calculations or references, YMMV.
Heating systems generally are more efficient when they need to output less power. Whether that cancels the increased heat loss seems to be a question that can’t be answered in general.
>Otherwise, this doesn't make sense from a physics standpoint. A temporarily lower temperature differential means less kWh of heat lost.
This topic comes up anytime thermostats and heating are mentioned. The physics arguments only makes sense if you don't care about comfort. Most people would rather optimize for comfort with some energy/cost savings if possible and the physics folks seem to not care about comfort at all.
"Quickly" implies higher power which will make the air around radiators warmer than a slow heating.
The losses are proportional to the temperature differential between outside and inside.
So you should have somewhat higher losses from the hotter air streams from the radiators passing the windows.
Dunno about magnitude though.
I think in real life there are more constraints. For example there are people that sleep better at a lower temperature than the daily one (so leaving the thermostat at the same temperature it's a minus for them).
Regarding "what is better" from energy efficiency, I would prefer a system that "check it" because my guess is that it depends a lot based on the individual situation. I mean everybody is going crazy over "IA" but a couple of sensors and a system smart enough to adjust your usage based on your particular situation and preferences (like "eco", etc.) is an exception.
In slightly cooler climates, the answer for sleep is to open windows. This works in much of Europe, even through summer.
But of course, not really feasible in Atlanta or Phoenix. Nighttime temps are too warm.
We are talking about places that need heating here.
In general, you should either run the heater or have your window open. Both at the same time is bad news for your energy bill.
Open windows in a city often means you are invinting in pollution, both air and noise.
Opening windows also helps to evacuate inner pollution coming from furnitures, wall paint, parquet and other chemicals...
Exactly. Current HVAC systems have extensive filtration; some HVAC systems have HEPA filters.
> the theory being that warming up a cold house in the morning costs more energy than maintaining a stable temperature.
That's true if you completely stop heating. However if you lower the temperature by roughly 3.5C when you're not home, you'll be saving energy.
So you can for example program it to be 16C when you're out and 19C when you're in. You don't completely turn off heating indeed.
(UK) my boiler has a control with something like the wake..leave timer (it actually has six settings for a midday period as well) and there is a separate thermostat with a temperature dial. The boiler also has a button that advances it to the next time interval if you want instant on (eg if you come home early to a cold house). I find this combo of controls meets all of my needs, given that I have a fairly repeatable daily schedule.
> the theory being that warming up a cold house in the morning costs more energy than maintaining a stable temperature
I've heard this theory a lot too, but it doesn't match with physics. A warm house loses more energy than a cold house, due to a higher temperature difference allowing easier heat transfer. So in most homes, with radiators and high temperature CV, it's way more efficient to just turn it off when you gone.
One exception is when you have a very well insulated house, combined with floor heating and a very efficient, low temperature heat pump. In this case, it takes a lot of time for temperature to move in the house and it's already incredibly efficient.
It does match physics if you consider other factors. Apart from the heat pump scenario, this statement can also be true when you have condensing boilers (and okay-ish insulation)
The reasoning: when you heat up the house, then your boiler needs to produce constant high-temperature water. When you keep the house at the same temperature, then the boiler produces much lower temp water and it is more efficient.
Insulation also matters because if your house has outer insulation then it means that heat transfer from the house to the environment is mostly blocked, but cross-room heat transfer is likely not (through the walls). Therefore it is better to heat the whole house than heating just a couple of rooms because if you do the latter then you'll end up heating the whole house anyway but you're using less surface area (meaning you need higher flow temperatures, meaning less efficiency).
> The reasoning: when you heat up the house, then your boiler needs to produce constant high-temperature water. When you keep the house at the same temperature, then the boiler produces much lower temp water and it is more efficient.
How does your boiler produce heat for your water in your scenario?
> Therefore it is better to heat the whole house than heating just a couple of rooms because if you do the latter then you'll end up heating the whole house anyway but you're using less surface area (meaning you need higher flow temperatures, meaning less efficiency).
Just model the other rooms as very weird wall to the outside.
We've used the Tado system with a central boiler and smart radiator knobs for a few years. It's worked fine and hooks up to Home Assistant and can do the things you describe. I'm sure there are some alternatives.
I have an Ecobee and I like it. It comes standard with Home, Away, and Sleep but you can put in as many or as few as you want. You can manually change the temp and you can also set how long you want your manual temp to “stick”. Either until you cancel it, or until the next preprogrammed change. I like it cooler at night, so I have it change temp around my normal bedtime, which includes if I adjusted the daytime temp because I don’t want to have to remember to change it back myself, that’s why I have a smart thermostat. It detects when I leave the house and sets it to away, because I don’t need it running as if I am at home. If I go on vacation I can set it to keep the house safe, but not comfortable, and change back around the time my flight lands.
Unless you have a crazy random schedule, or you want the temp the same whether you are asleep, awake, or not at home, or i guess if you have different temp preferences every day. Otherwise you can program in a basic schedule and just adjust manually as needed. Nothing stops you from changing the temp manually if you wake up an hour early, but if you wake up on time, then you don’t even have to think about it.
>I guess I’d be happier with a more programmable thermostat that I could set to behave like an old school dial thermostat.
I honestly prefer the older type. Ours is programable, but we just don't program it and always just set it to the temp we want. If we are feeling a little chilly on a cold day, we'll bump it up a degree, or down a degree when it's particularly sunny and everyone is feeling warm.
Isn't this pretty much what these thermostats already allow? I have a new Honeywell Thermostat which basically does what the twenty years old one it replaced does with a few added conveniences in terms of UI. It has those wake/leave/return/sleep instants for each weekday (but also adds an optional second leave/return pair), and it has an option to override the day programme to 'holiday', which is essentially an eighth programmable weekday you can activate at any time.
Your use case is possible with that. Just set the standard program to 15°C, and activate the holiday set to whatever you need whenever you want. Configure it to go to 15°C at some sensible time in the evening, so it won't go on even if you forget it.
15 C is very cold. Are you American?
15°C would be the standard setting of 'no heating' (just keep the house warm enough to avoid mould and such). The 'holiday' programme would be 21°C or whatever is desired. That would effectively turn the thermostat into one where turn on the heating by putting it in 'holiday' mode, and can turn it off by exiting that mode or just letting it revert to 15°C after 23:00 or so.
Comment was deleted :(
The obvious solution is a "wake time" of 8 am, "leave time" of 8:01, "return" 8:02, "sleep" 8:03. Then just set the sleep temperature to your desired temp and the remaining ones to something reasonably close, or if it doesn't automatically switch between heating and air conditioning, set it for the no-op for the season (i.e. the highest possible temp in summer, and the lowest possible in winter) for those three minutes.
> I wonder what the ideal one-size fits all thermostat looks like
https://www.honeywellhome.com/us/en/products/air/thermostats...
My wife and I worked a six-week shift work schedule for a long time. We got second-gen nest thermostats when they first came out (2012) thinking they were neat.
Nope! The smart learning feature was the biggest pain in the ass. You’d be sleeping during the day for a night shift, only to find yourself freezing because it decided no one was home.
I like the Nest, but I absolutely turned off all the "smart" features and just set a fixed temperature range and change it when desired.
Mine works OK as long as presence detection (using people's phones and Google Home) is operating correctly.
Everyone leaves, and the thermostat adjusts.
Someone comes home (or walks in front of it), and it goes back to the normal setpoint.
Sounds easy. Isn't always easy.
The reliability of this seems to be highly dependent on the phone(s) themselves simply succeeding at not killing useful processes.
Overall, I'm not entirely displeased with it. I procured it very inexpensively by buying it from one of my energy provider's online store in conjunction with a substantial rebate from my other energy provider. I'm confident that it paid for itself very quickly, and it's nice to be able to set the thermostat remotely.
My lament is that there seems to be approximately nothing I can do to improve the presence detection function without gymnastics or spending real money. What I want is a local API that I can enable and do stuff with; what I get is "Good luck! Have you tried buying Nest Protect subscription motion detectors? (Oh lol, we stopped selling those.)"
(I'm OK with the privacy and security aspects of what I'm trying to do. I'm not OK with having a connected device that I can't bend to my will. I'm even less OK with more recurring expenses. The next thermostat I buy will have local control over the LAN, but it probably won't pay for itself quite as quickly as this one did.)
[note: I've never played with the auto-schedule "learning" function at all. It always seemed like a complete waste of time, since I for one do not have a regular schedule.]
You can turn off the feature that changes temp based on presence. Or disable dynamic scheduling altogether.
I ended up having to manually changing the schedule week-to-week.
> ideal one-size fits all thermostat
The round Honeywell electromechanical thermostat with a bimetallic strip, invented in 1953: https://www.honeywellstore.com/store/products/honeywell-roun...
24VAC, dead simple, and reliable. My family’s lake house has 50+ year old Honeywell round thermostats still in service.
> I wonder what the ideal one-size fits all thermostat looks like.
As you go on to describe, there probably isn't one.
I guess your toolbox really shapes your solution space thinking; as I read through this, being completely lost in the whole world of RF whatnot, my mind jumped straight to an alternative attack that better fit my own tooling: could you encase the thermostat in a box that you can mechanically control the temperature of?
I removed the thermistor from inside my wall controller and wired in a digital pot instead. Achieves the same thing without physically heating and cooling the sensor
Or attach an ESP32 to the boiler's control board that closes a dry contact circuit...?
The problem is, if your landlord ever comes around for inspection, or the bloody thing breaks down due to your installation attempt, you can be held liable up to and including getting evicted.
Where can you get evicted for something like that? The worst case is that they would sue your insurance for damages, or you'd have to pay them out of pocket.
Many countries have no contest evictions, so you could even get evicted if the landlord doesn't like your cooking.
Probably half of the US, but messing around with stuff like boilers can and will lead to issues even here in Germany.
That was my first thought on how I would approach it as well.
This sounds good, except that cooling a box is problematic. He needs the temperature sensor to read low so that it turns on the heat.
That said, if he has access to the interior of the thermostat, I'm sure it won't be difficult to replace the temperature sensor with a circuit to cause it to read either really high or really low on demand.
For such a minor use case a peltier element is suitable. Very energy inefficiënt but you don't need much and it can both heat and cool.
I was literally imagining duck-taping one of those cheap electric "instant cooling" cups over the box on the wall, and running a small incandescent bulb in to be the heating up element.
> This sounds good, except that cooling a box is problematic. He needs the temperature sensor to read low so that it turns on the heat.
Ice pack and desiccant?
Yes! You can indeed do exactly this. Look up CoolBot - they do exactly this, by just heating up the existing thermostat
Or, assuming they have physical access to the combi boiler, removing the receiver unit and replacing it with a more Home Assistant friendly combi boiler thermostat.
Probably a 30 minute job if you’ve never done it before and easily reversible with a little bit of double sided sticky tape, which all Brits should be familiar with if they ever made a Tracy Island. There is a real risk of electrocution which could be completely militated against by turning off the power to the boiler.
Still, a fun hack, and nicely executed!
I've heard a story of people renting an apartment with locked thermostat to the legally allowed minimum. Tenants would put ice on the thermostat
I heard that was a well-known trick at my old uni dorm. There was a single thermostat for the whole floor so once people figured out where the sensor was, the ones who lived closest to it would often leave packs of frozen food on it.
I would probably just go about this by heating/cooling the thermostat itself rather than messing around with radio signals. Put a little box around it and something that could control the temp in the box, like a little peltier element. When you want the heat to run, cool the inside of the box. When you want it to stop, warm it up. Etc.
But then I build thermal control devices for fun so maybe it just seems like a much easier method to me.
X-10 devices [0] that do this have been around for a long time. I've even seen elaborate setups that can be controlled via a landline.
[0]: https://thex10shop.com/products/x10-powerhouse-th2807-thermo...
If you do want to decode it, it's probably not that hard. I was going to implement the transmission side when I did this, but then I moved.
The Flipper Zero is great, and could handle all of the hacking/investigation part by installing custom firmware.
The original product understandably arrives with heavily-restricted firmware (I imagine to reduce the amount of flak the company receives). However, it is incredibly easy to install Flipper Unleashed or similar, which removes all said restrictions and adds a lot of additional functionality.
Possessing the tools that could be used to commit a crime is not necessarily a crime in and of itself! Just be careful with what you do or, depending on what country you’re in, you might find some men in suits knocking at your door.
Personally, I wanted to replay “encrypted” 433MHz signals for my own devices (electric gate, roller door, roller shutters, …) and this was disabled with the Flipper’s region set to Australia.
> Possessing the tools that could be used to commit a crime is not necessarily a crime in and of itself!
While I do agree 1000%, I also want people to be careful with this thinking since I have gotten in some minor trouble in the past. Always assume the authority questioning you can and will create whatever narrative they wish, that it will be accepted, and that your own reasoning will likely be used against you.
I will always encourage exploration and curiosity in tech, but if we stick with the Flipper Zero example, there's a few things one should keep in mind, regardless of the jurisdiction they're in:
* Don't carry it around unless you intend to use it.
* Read all documentation before you start practicing, then practice being subtle.
* Taking a note from my outdoorsy side, adopt the "leave no trace" ethos.
* Pay attention to the effect your presence and actions have on the environment and your target and how that might be interpreted by an outside observer, then take action to mitigate suspicion.
These apply to lots of devices, everything from your disposable smartphone to a cheap RFID card copier from Temu.
Our eagerness sometimes gets the best of us, especially new-comers, and we want to jump to the part where we can be like the hackers we see in tv and video games. There's a reason those guys are fictional characters. Innocuous actions or not, the perception of the authority questioning you is all that will matter, in the end.
> "Always assume the authority questioning you can and will create whatever narrative they wish, that it will be accepted, and that your own reasoning will likely be used against you."
And with that, I give you:
Don't Talk To the Police:
Would really like GP's thoughts on this. Sounds like they were questioned but not indited, the thing which the cop in that video denies ever happened. It also depends on the country. Watching police shows in NL, everybody talks and it often really does matter what they say, e.g. for the police to believe whether that bicycle is theirs, or whether they get a contact prohibition to their ex (where someone has to make the decision whether their request is reasonable), etc.
Do heed what's mentioned in the video, it's mostly true I presume and probably doubly so for their country of origin, but also consider there exists a balance
Or perhaps go for the opposite of subtle - in many places it's quite normal to see people in hi-vis vests taking readings etc.
That's an excellent additional thing to consider and I'm a bit mad that I neglected it since I have accidentally been that guy.
My job requires me to wear hi-vis (as well as other PPE) and it is crazy how little security pays attention to me in some of the very-big-name plants I visit, often with a laptop bag full of flash drives and a bunch of other tools that allow me to get into the machines.
Early in this part of my career, I found myself in a very large plant for the first time, and my escort got pulled away on some other task (I now expect this to happen since it's such a common occurrence), leaving me to fix the machine I was working on. The place was the size of a small town, and I needed to use the restroom, but nobody was in the vicinity to ask, so I did my best to follow the floor markings and signs. Found it, but took a wrong turn coming back and found myself in a completely different area. Since I was new, I tried to find my way back without asking anyone I saw because I did not want to look stupid, but nobody stopped me, questioned me, etc.
Probably one of the best lessons in social engineering is looking like you're supposed to be there.
One should not practice these things in actual high security areas, but it can be fun to simply walk around a strange place with a look of purpose and velocity. Not making eye contact, perhaps on a phone. As long as you won't get in trouble it's easy to practice the body language of belonging and that skill can be really useful even if you are not trying to use it for malicious purposes (i.e. if you are actually supposed to be there, the best thing for everyone is you look the part and don't cause more worry than required).
I used to do contracted engineering and maintenance work in railyards, and in each facility would obtain (always with permission from my recollection) a well-worn supervisor vest and hard hat. They are usually color-coded.
The 'shade curve' as I call it, where one reaches a point where their actions could be considered so shady, it's automatically assumed it couldn't possibly be them.
Smoking pot in a dark parking lot with friends at night gives more cover, but smoking pot walking down your city's main street in the middle of the day gives you the cover of just smoking an innocuous "rollie," like any other person could be.
It's hard for anyone with a nose to mistake one for the other.
(The underlying point is completely valid, though. Audacity is a powerful thing.)
If OP ever shows up here, you probably could have just replaced the thermostat with one that is compatible with your boiler for less money and headache. The boiler market is fairly open to competition as evidenced by the fact that you could find a Honeywell signal in a random OSS project that also worked.
Good luck with your future apartment customizations!
I think you missed where it was explained that the apartment is rented and therefore you cannot modify anything.
Cannot modify irreversibly though right? Something like a Nest or whatever is easy to return to the original state when you leave.
Depends where you are. Where I live it's no modification. If it's hard-wired the tenant can't touch it.
Though in reality many landlords don't mind as long as you know what you're doing and return it to how it was. Just a problem if you get a jerk landlord.
Except how does the landlord know? Surprise inspections? And what are the penalties? This should all be spelled out in the lease contract.
Depends on jurisdiction, of course, but often you’re allowed to modify things as long as you return it to how it was before when you leave. Obviously not quite as simple as that always but I would guess in many placing temporarily replacing a simple thermostat would fall under that.
Replacing a thermostat is very easy to do though. And very easy to revert too.
Usually it's just acting as a simple relay (on-off switch) so there's two physical wires.
I've got my Hive thermostat running great with various Bosch and Vaillant boilers. And it works great with HA.
Some newer boilers have 12V "smart" controls but still expose 230V "dumb" call for heating pins.
OP's thermostat wasn't wired, that's why he'd need the electrician.
Agreed (I set up our dual zone Nest-controllee heating so I know it's not difficult), but what happens if the landlord visits and isn't happy with you having done this? It would be a pain to have to revert this if you knew the landlord was coming.
Check your local laws. You may be allowed to do something like this by law.
> Usually it's just acting as a simple relay (on-off switch) so there's two physical wires.
Vaillant has a proportional signal as well, and that thing in my old home was 30 years old... [1]
[1] https://www.mikrocontroller.net/topic/126250?page=single
You just take the thermostat off the wall and put it in a drawer and then you buy a new thermostat and put it on the wall and then when you give the apartment back, you take the old thermostat and you put it back on the wall
Also, if you read this far, are you German or something? you can just do things. which OP seems to know. And even if the landlord came and saw the apartment as long as the new thermostat isn’t neon orange, he isn’t going to notice and even if he somehow noticed you would just gaslight him and say no that’s how it’s always been and how the hell is he gonna escalate past that? And why would he if the new thermostat is more expensive and has better features?
Cool project.
Speaking of newish natural gas (CH4) heaters, they all should have modulating thermostat capability with OpenTherm/eBus or other protocol. Combined with a thermostat with outdoor temperature sensor system efficiency is increased a few percent and that should help offset thermostat and installation costs. In the end you have more efficient modern heating system.
Same should apply for heat pump systems.
OpenTherm is a cool idea but even new installations aren't always wired for it. When installing a new smart thermostat I found the installation has been wired as S Plan with the few cables running between the boiler location and valves location already consumed. Makes the job much bigger if you're not prepared for it.
There are many wireless OpenTherm thermostats. Wired is better but is not required for modern thermostats.
We've moved to an new apartment (house) and we had to do a full renovation. It doesn't have modern insulation and I calculated that for the time being the ROI on insulation isn't worth it. It's a multi-floor semi-detached house and I wanted the best comfort and the most economical heating possible.
In particular: stable and individually adjustable temperatures for bedrooms and living rooms; underfloor heating in some rooms (bedrooms), radiator-based heating in some others (living room), and combined UFH+radiators in some others (where UFH might not be enough during extreme colds).
I thought I can just pay someone some money and they'll set up the controls for me. It must be a simple exercise, right?
I could not have been more wrong. After spending a few hours of understanding the setups that "experts" have recommended, I figured out edge cases where they would be either wasteful or uncomfortable (meaning: unnecessary and inavoidable temperature overshoots or undershoots, etc.). I had many-many rounds with Honeywell, Tado, Siemens, etc. and every single one of them had _major_ issues.
The renovation got a bit stuck because of this, but the plumbing was ready so I wanted to see whether the pluming and pumps are working, at least. So I connected the pumps and valves to "smart plugs", i.e. Zigbee-controlled plugs, so that I can see that they turn on. They did, which got me thinking...
Right now I have $20 Zigbee temp sensors sprinkled across the house, $30 smart plugs and relays driving valves, pumps and the boiler, and Home Assistant is controlling the whole thing. Everything works perfectly and I could implement some features that simply no system would have done out of the box, for example in rooms where there's combined UFH and radiators I can drive both heating systems when the target temperature is far from the desired (so that the room heats up quickly) but as the room temp is getting closer to the target, the radiators are turned off so that UFH dominates heating (more comfortable and more energy efficient than radiators). In rooms with radiators, temp is +- 0.4 C within target, in rooms with UFH, it's +-0.1C within target.
Yeah, the automated/remote controlled heating system world, and also the ringbell world is basically a giant scam, since they are updates on world that also scammed you in the past. I cried when I shelled out so much money for my Tado device, but even a dumb bTicino device costed in the hundred of euros realm, and it's just a sensor + a small LCD display and a designed-in-hell menu system to program it. And the same happens in Ip-based ringbells. A Doorbird will cost you hundreds of euros for what is basically a webcam plus some nice metal casing and a shitty software, but it competes with analog systems with optic cables etc that cost basically the same or more.
Off the shelf systems aren't only optimised solely for efficiency. They're made to be simple enough that an installer with half a day's training can do a few multiplications and additions to set the parameters that'll give you a tolerable percentage of optimal in the situations that equipment is specified for -- while still being understandable by the next guy. This nearly always means things are a bit oversized and inefficient to account for the things that the simple models are missing.
Almost everything in engineering is like this, not just heating. It's pretty rare that something is fully optimised.
Sounds like a nightmare for a future buyer to operate.
Some people are unlucky enough to buy homes where a machine engineer designed the boiler setup and the boiler room have enough valves and manometers to like operate the engine of Titanic.
I guess programmers are the new sinners in this area nowadays.
If we ever sell this (which we don't plan to), I know what to install (it'll be quite good, just not this perfect). I have it in a cupboard (a Siemens Connected Home thermostat system), the downside of that is that the combined UFH+radiator rooms will be less comfortable.
(But still more comfortable than 99% of the houses I've been in.)
I haven't mentioned in the parent comment but as a test I've dismantled the HA system and installed the Siemens system and it works well, just not 'perfectly'.
Sounds well thought out. Many seem to forget designing for replacing.
In generall I think all these IoT systems will be a major headache as they age.
My thermostats on the radiators are 45 year old by now. That is kinda the expected service life we are used to.
The existing professional setup was also a nightmare, what gives?
Well first of I am envious and I would want to do something similar.
If I inherit a heating system I want it to be all mechanical except maybe the control system for any heating pump.
I'd like more details on your home assistant setup as I'm trying to optimize mine.
Btw, you can use $5 LYWSD03MMC thermometers with ble or zigbee.
For every John Siegenthaler and Dan Holohan, there are thousands of mechanical engineers and tens of thousands of plumbers who are happier to slap in a $20K 4-hour boiler retrofit. There’s not enough extra money in catering to the 0.1% of homeowners who care about the details.
A lot of this is so easy with AI now. Just need some confidence and patience to work with AI lol.
It’s a service or human engineering problem rather than a mechanical engineering or knowledge problem.
Contractors today put in over-sized equipment, set flow temps higher than needed, undersize emitters for aesthetics and cost, and run pumps at full speed to avoid callbacks for “it’s too cold”. You can’t afford the windshield time to drive over to tweak the system to extract maximum performance, because homeowners don’t want to pay for it and will go with the lower bidder enough times that your premium AI-powered service will struggle.
I’ve tweaked my reset curve 12 times the first winter and 2 more times since then (counted from my spreadsheet).
Realistically, if I gave up on the last 3% tweaking, we could have lived with it after 2 post-install tweaks, but at least one of those had to wait for seriously cold weather snap to fine-tune the low end.
My spouse would happily agree that the house is finally very comfortable and noticeably more than before. She’d also tell friends who asked that there were a few days the first winter where the house wasn’t warm enough and needed an adjustment. People who heard that story might conclude that their neighbor’s guy who never has a callback for “too cold” is a safer bet.
Over time, I think even the best mechanical contractors will start to lean towards avoiding callbacks and do that by running the system 5-10°C hotter than “correct” engineering requires. That’s still better than today, where flow is set to 80°C, pumps to max, and the thermostat cycles 4 times an hour but the house is never too cold.
a bit off-topic: Are you running a single boiler and if so, how are you mixing UFH with radiators given there's a ~20C difference between the recommended temps for the two?
My knowledge is that for UFH you run at temps between 40-50C and radiators run at 60-70*C.
UFH has mixing valves, so it runs on 38 C and radiators run on 55C. Single boiler.
> I could not have been more wrong. After spending a few hours of understanding the setups that "experts" have recommended, I figured out edge cases where they would be either wasteful or uncomfortable (meaning: unnecessary and inavoidable temperature overshoots or undershoots, etc.). I had many-many rounds with Honeywell, Tado, Siemens, etc. and every single one of them had _major_ issues.
Temperature hysteresis is unavoidable with a conventional thermostat, but you can reduce it with PID controllers. Most commercial building automation systems use PID controllers extensively.
My guess is that the residential options from Honeywell, JCI, Siemens, Trane, Carrier, etc are focused more on one-size-fits-all applications, whereas commercial BAS systems are more or less bespoke designs for a specific building (using commodity sensors and controllers). I work with all five of the aforementioned companies on building automation projects, FWIW.
> We've moved to an new apartment (house) and we had to do a full renovation. It doesn't have modern insulation and I calculated that for the time being the ROI on insulation isn't worth it.
You calculated wrong, guaranteed. Most likely, you wildly underestimated fuel/electricity costs.
> After spending a few hours of understanding the setups that "experts" have recommended, I figured out edge cases where they would be either wasteful or uncomfortable (meaning: unnecessary and inavoidable temperature overshoots or undershoots, etc.).
Instead of thinking "the entire HVAC/heat industry are idiots who can't do any of this right", maybe you should take a look in the mirror and consider that your assumptions and/or criteria are wrong.
For example: under/over shoots in a modern HVAC or heating system will not cause any "waste" or discomfort. 1-2 degree F in overshoot does not mean the space will lose appreciably more heat than if it had perfectly regulated at the setpoint. You also don't want a system that responds instantly. Let's say you open the door to receive a package, and you're signing paperwork, etc. You close the door. The air in the room is substantially cooler.
Should the heat turn on?
I bet it does in your home...but the correct answer is no, because the air will warm up rapidly from all the objects that were at the temperature of the room. Thousand-plus square feet worth of surface area...
One doesn’t actually need any extra hardware for this… just 8cm of wire and this https://github.com/F5OEO/rpitx
(use at your own risk of course)
From the linked repo:
> rpitx is a general radio frequency transmitter for Raspberry Pi which doesn't require any other hardware unless filter to avoid intererence. It can handle frequencies from 5 KHz up to 1500 MHz.
Wait, how does that work?
1.5GHz is a _lot_, I can't imagine this is done with bit-banging an I/O line, nor do I expect the Pi will have a DAC with anything close to a 3GHz+ sample rate.
> Plug a wire on GPIO 4, means Pin 7 of the GPIO header (header P1). This acts as the antenna.
A bit of Googling shows me that on the later Pi board GPIO4 (pin 7) has a bunch of alternative modes, amongst which is a general purpose clock output (GPCLK0), a DPI output bit (DPI_D0) and what I recon is composite analog video in/out (AVEOUT_VID0, AVEIN_VID0), and the TDI JTAG pin. But none of these would get close to 1.5Ghz TRX capabilities, no?
What's the magic here?
RF is basically black magic but here it’s the harmonics of lower frequencies that are in GHz range (and very noisy and weak)
This did come up when I was researching this but it’s incredibly dangerous as you’ll be spewing all over the spectrum due to harmonics, I considered it too much of a hack for my liking
> sledgehammer approach
A hammerier solution would be to control the temperature seen by the thermostat (ignore the difficult RF protocol).
A heating element and a temperature reading could control the heat seen by the thermostat.
I'm pretty sure you wouldn't need any cooling (Peltier or whatever). Just a heater and ambient cooling! Set the thermostat to a high temperature, and run the heater to make the measured temperature hotter: when you don't want the heating to run.
That said, I think hacking the RF protocol is geekier and far awesomer.
> Please do your due diligence and check local laws before attempting anything I do in this post. Transmitting radio signals can become legally problematic very quickly, and the band I specifically transmit on here (868Mhz) is illegal in the United States without a license. I'd rather you didn't have men in suits knocking on your door on my account. You've been warned!
Let's be honest here: the FCC is gonna have to see a helluva lot of problems coming from your transmissions before they bother to send the black Suburbans filled with men in suits to knock on your door. You're going to get a series of letters that basically say "please don't do that" if anything.
An American thermostat would be using around 920MHz which is the equivalent unlicensed band in the US. Funnily enough, the author warns Americans as an example but he is running more foul of the local rules an American would be (assuming an American would use 920MHz and not 868MHz).
In the US you are allowed to tinker around there with home-built RF devices for personal use and prototyping in unlicensed bands, to some extent. Although, using an SDR for this requires a certain interpretation of the rules. In Europe it's basically not allowed, one shall only use pre-certified modules. Or only use the device you've built in an RF anechoic chamber until you've undertaken the certification process (totally impractical for a hobbyist).
Funny how the manufacturer proudly claims that the protocol is encrypted, but completely forget to mitigate replay attacks,thus making the encryption completely useless
Which raises the question whether the OP now unknowingly also controls the heater in the apartment next to his...
Unlikely. This kind of wireless thermostat has two parts: the thermostat itself, and a separate receiver box that's directly connected to the boiler. There's usually a pairing process that you can go through where the two parts negotiate a shared value used in the protocol; this prevents one thermostat unintentionally controlling other boilers. You can see this described in the Installation Guide for the thermostat linked from the article (it's called 'binding' in the guide).
Probably not otherwise the original would also potentially run that risk
Good point!
The thermostats are paired, if my setup was able to control another apartments boiler then the original thermostat would also do that
And so the heat-stroke-killer was born, offing his victims with rapid changes between coldest and hottest setting, natural death has never been this human-made.
Ah yes, the classic problem of people using crypto primitives without fully understanding the problems they're trying to solve. Anyone even remotely interested should look into a full protocol like TLS or PGP to see how many primitives like block ciphers, hashes, etc. are involved and why.
> The only thing I'm not happy with is needing to use a very powerful and versatile radio like the HackRF for something as simple as a boiler on/off switch. But I'd rather use something overkill and have it work than spend ages trying to force smaller radios to do my bidding.
All the apartments I lived in had basic thermostats; and I even rewired and replaced one of them.
What was blocking Videah from buying an off-the-shelf thermostat?
I’ve got a similar problem, and plan to replace the thermostat with a Shelly relay which can be toggled by home assistant’s events based on the TRVs in each room.
Then the boiler is basically controlled by the relay.
Cool as fuc + very nice blog design.
Furry cartoons are catching on.
The legit Hackrf One is known to have frequency smearing, I wouldn’t use one off Aliexpress to transmit without testing it with a spectrum analyzer first (which you probably don’t have if you are buying knockoffs from Aliexpress).
What does frequency smearing mean in this context?
You're trying to transmit (only) on e.g. 433 MHz, but you actually transmit on 433 MHz and a bell curve around it.
so, severe LO clock drift?
Not exactly, the transmitted power tends to be centered on the frequency you desire, but there are unwanted harmonics off the center frequency. Its like having a fire hose that hits the desired target with water (something on fire), but it also hits everything else around the target in a large radius as well which may be very sensitive to water (precious art, high power transformers, etc)
The blogpost mentions "I guess it's always good to have another SDR just to confirm that we're not polluting other frequencies." and they have an RTLSDR which probably could serve as a good enough spectrum analyzer for this use case?
Some risk of collateral damage in the form of randomly controlling other peoples' boilers if your transmitter turns out to be more powerful than the one in the thermostat, tho...
I imagine even encrypted messages could be replayed if the protocol wasn't designed against it. It also doesen't say what kind of encryption it uses, it could be a very weak in-house "encryption", for all we know it could be only an unknown encoding.
The thermostat is paired with the boiler, the signals bundle the unique ID’s of each so this won’t happen. Otherwise there would be a risk the original thermostat would do the same.
In the former Soviet Union we just have central heating
The government maintains indoor temperature at 24 degrees from October to May, and the water is heated at the power stations.
And a €500 heating bill every month.
Jesus that sounds miserable. Sleeping at 75F?!
Could the same radio be controlling other nearby boilers unintentionally?
Instead of attacking a radio controlled relay, the author should have read up on how their heating system works. All they need is a relay controlled by an internet connected thing to replace the thermostat receiver. I could understand if the receiver was locked away but the video clearly shows they have access to the boiler.
That leaves very visible evidence that things have been hacked. Any time the landlord comes around you'd want to remove that. And if there's some sort of infrastructure emergency (plumbing problem, heat goes out, fire in the building) it could be very challenging to get there and remove all traces before the landlord is stomping around.
Why would you be that paranoid? What laws exist in the UK where this is so illegal as to be that paranoid?
That's a level of paranoia I would never have. You can easily conceal them in a way that is almost imperceptible.
The UK's Online Safety Act is pretty horrific. Our friends in the UK have my sympathy.
I went through various stages of this myself and got an Sonoff RF Bridge, that allowed me to capture and replay RF via Home Assistant. In the end though, it was always easier to use an off the shelf solution, especially for boilers. OpenTherm with Tado worked perfectly.
I need this solution
Our landlord installed a Honeywell home, the cheapest version, and it has no remote or timer capabilities
And especially in winter it would be nice if it would jump on before we wake up!
I just gotta say, I really like the animated gifs. Kudos to the blogger.
I would have put a peltier/TEC below the thermostat to influence it's measured air temp vs resorting to reverse engineering and illegal signal broadcasting.
If I understood the OP correctly, then the broadcasting would only be illegal in the US.
Yes but no: The original device operates in the 868MHz band, which is a ISM band in the EU. However this band isn't availabe for public use in the US (IIRC some mobile phone cells operate in that band) - so the original thermostat is already illegal to sell/buy/use in the US.
If you bought such a thermostat in the US (e.g. at walmart or what-do-I-know), that device would probably operate on 433 or 915 MHz. I think you can legally broadcast on these in the US, much like the OP did [in the UK]. Power limits might be a bit different and such. But IANAL and no US person, so do some research before grabbing a HackRF One ;-)
Is this a non-standard thermostat control mechanism? I don’t know what’s common in apartments. All my houses have the thermostat wired to the HVAC (and are easily replaceable by the resident).
Men in Black suit knocking on the door for this is a First-world thing.
loved the blend of reverse engineering and persistence
This is basically why companies like HeatWatch have 90% market share for NYC landlords
Very interesting ending of the post:
```There was a comment section here. It's gone now. As of March 16th, 2025 the United Kingdom's Online Safety Act has gone into full effect. The law presents a lot of challenges for hobbyist websites like this one to present any user-to-user content (like y'know, blog comments) and comes with some pretty serious repercussions for non-compliance.
The odds of Ofcom (the regulator whose job is to enforce this) kicking my door down over this blog are low if we are being honest with ourselves. But the odds are at least somewhere above zero and the punishment is a life ruining £18 million fine(!!) so it's just not worth the risk.
A kind lawyer has written up the implications of this law for self-run blogs like this one and the only way to guarantee that I am not in-scope would be to manually review all comments made before being available to the public. Not to be a big baby about it all but I don't really want to do this! I liked my current setup!
So I guess as a little act of protest and to hedge against any risk I've removed the comment section entirely. Sorry about that!```
For a related hack... If your apartment building with a BACnet system, it also relies on a set of commands for heating and cooling. Assuming you are on the same VLAN as teh server, you can inject commands. The difficulty is that every BACnet server is somewhat different, though most have spec online.
OP removed their comment section, but if you’re here:
I haven’t done this since 2014 but the google nest API used to (hopefully still does?) let you see and or set the thermostats status with curl commands.
My use case was to run one shell script that got my burglar alarms status, and if it was “armed/away” to simply set my nest thermostat as away, too.
But it can also be hooked up to a dummy load or a relay and just used as an indoor temperature sensor.
And the curl commands OP is relying on can be tied in to indoor and outdoor temperatures , such as scraping local weather with curl/wget and based on that integer, turning the boiler to a minimum when it’s a certain temperature outside.
Or turning it completely off when it’s warm outside.
I’m about to revisit this again just because I have an ancient gas pig of a furnace that uses microvolt and is too cold when it’s cold outside, and too hot when it’s warm outside.
So I need one thermostat in place to turn it on no matter what at 40F, but then some conditional logic to kick that thing on and off on different cycles based on outdoor temps. The whole systems too crude to implement one off the shelf without adding a zone controller, so I just want a Linux box at home to be the zone controller….
where I differ is that I’m not sending an RF signal to the boiler, I just have to close an NO contact to engage mine (and I’m lazily going to use the nest for that.)
If anyone knows of a better thermostat that has its own API I can set, read sensors, turn hvac on and off without using google/nest account or having a dependency on the goodwill of their API existing forever , I’ll come back and glean any responses thanks in advance.
As an afterthought, hm I can just attach temperature probes and a GPIO for a relay and indoor/outdoor temps and do away with google/nest altogether…. Thanks for jogging my brain a bit I might do exactly that.
(The nest was cool , and educational, I guess, 12 years ago when I didn’t know how to really do anything but run and fire off curl commands on someone else’s hardware for temp sense and closing a relay and I don’t have anything bad to say about it as a starting point.)
Where I was going with this , though, was that , you could use an off the shelf nest , and run
1) one command against API to get thermostat status (system thinks it’s on or off , even though it’s factually not directly controlling anything) and then based on that,
2) another command to your RF board to transmit a matching signal.
…
(However you could also do the same with a temperature probe that can be read on board or over WiFi , and then manage your setpoints in the script and or by other means: eg scraping a weather site for the local outdoor temp in your case where the landlord probably wouldn’t let you attach or connect an outdoor probe.)
Bonus with the nest approach is you get a dial, can mount it on anything , doesn’t have to be the wall of your unit… and it “sort of works” like a normal thermostat as well, as soon as the shell script reconciles the two states manually.
Long winded rant but the original use case was an apartment where the thermostat was proprietary and serialized data and I didn’t have any option to integrate a smart thermostat other than turning it to its maximum set point and then using the nest with a massive 220V/50A HVAC relay to just chunk the AC power line on and off on demand.
What is with this absurd headline? Imitating your RF thermostat isn't "attacking" anything.
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if i had a nickel for every time someone said the word "objectively" to make something seem more true when it's just, their opinion, man... i would be rich enough to lobby for government-mandated fursonas
Crafted by Rajat
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