6 ms·

> 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 getti

> 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.)

frereubu 2y ago
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?
- sokoloff 2y ago
  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-system-maximum-energy-savings/ https://kw-engineering.com/how-to-optimize-condensing-boiler...
  - Retric 2y ago
    > 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.
    - sokoloff 2y ago
      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).
  - frereubu 2y ago
    Thanks for the explanation.
  - eru 2y ago
    Btw, a heated blanket would be a lot more efficient, as it warms just your butt.
    - sevensor 2y ago
      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.
      - pests 2y ago
        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.
  - amluto 2y ago
- leoedin 2y ago
  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.
  - frereubu 2y ago
    Thanks for the explanation.
  - looofooo0 2y ago
    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. )
- rsynnott 2y ago
  > 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...
  - looofooo0 2y ago
    ISO 7730 to the help. Just keep low overall temperatures and heat 24/7 in a reasonably insulated home.
  - lucb1e 2y ago
    > 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
Retric 2y ago
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.
- DamonHD 2y ago
  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.
  - HPsquared 2y ago
    What do you do for ventilation?
    - DamonHD 2y ago
      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-ventilation.html https://www.earth.org.uk/MHRV-mechanical-heat-recovery-venti...
  - sudahtigabulan 2y ago
    Do you mean you moved them to another wall, or just increased the gap? (not a native speaker here)
    - 2y ago
sz4kerto 2y ago
> 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.
- sokoloff 2y ago
  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.
quickthrowman 2y ago
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.
deleted 2y ago
[deleted]
looofooo0 2y ago
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 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.
- static_motion 2y ago
  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.
  - looofooo0 2y ago
    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.
    - walrus01 2y ago
      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.
      - looofooo0 2y ago
        Not true, I can buy a Chinese 4kw Model for 650€ which can heat till -15degree. Doubt that you can save much.
        walrus01 2y ago
dheera 2y ago
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.
- organsnyder 2y ago
  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.
eek2121 2y ago
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”.

frereubu 2y ago

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?

sokoloff 2y ago
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-system-maximum-energy-savings/ https://kw-engineering.com/how-to-optimize-condensing-boiler...
- Retric 2y ago
  > 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.
  - sokoloff 2y ago
    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).
- frereubu 2y ago
  Thanks for the explanation.
- eru 2y ago
  Btw, a heated blanket would be a lot more efficient, as it warms just your butt.
  - sevensor 2y ago
    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.
    - pests 2y ago
      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.
- amluto 2y ago
leoedin 2y ago
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.
- frereubu 2y ago
  Thanks for the explanation.
- looofooo0 2y ago
  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. )
rsynnott 2y ago
> 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...
- looofooo0 2y ago
  ISO 7730 to the help. Just keep low overall temperatures and heat 24/7 in a reasonably insulated home.
- lucb1e 2y ago
  > 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

Retric 2y ago

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.

DamonHD 2y ago
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.
- HPsquared 2y ago
  What do you do for ventilation?
  - DamonHD 2y ago
    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-ventilation.html https://www.earth.org.uk/MHRV-mechanical-heat-recovery-venti...
- sudahtigabulan 2y ago
  Do you mean you moved them to another wall, or just increased the gap? (not a native speaker here)
  - 2y ago

sz4kerto 2y ago

> 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.

sokoloff 2y ago
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.

quickthrowman 2y ago

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.

deleted 2y ago

[deleted]

looofooo0 2y ago

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 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.

static_motion 2y ago
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.
- looofooo0 2y ago
  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.
  - walrus01 2y ago
    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.
    - looofooo0 2y ago
      Not true, I can buy a Chinese 4kw Model for 650€ which can heat till -15degree. Doubt that you can save much.
      - walrus01 2y ago

dheera 2y ago

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.

organsnyder 2y ago
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.

eek2121 2y ago

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”.