4 ms·

> Heating a building when you aren't there is silly. Is this true? I've thought about it for a while but can't quite wrap my head around an answer that feels o

> Heating a building when you aren't there is silly. Is this true? I've thought about it for a while but can't quite wrap my head around an answer that feels obviously correct. It takes a lot of energy to raise the temperature of a house - more than to maintain a given temperature. Allowing for changing temperatures during the day, and concrete slabs and walls and the ground as heat stores, is it always the case that it uses less energy to have a lower set point while you're out and raise it when you get home than to just keep it at the comfortable level the whole time?

cmrx64 6y ago
> It takes a lot of energy to raise the temperature of a house - more than to maintain a given temperature is this true? the house is constantly bleeding off its heat at a rate proportional to the temperature difference between interior and exterior. it should always cost more energy to maintain the higher temperature gradient than to just let the heat bleed off (which it was always going to do) and add in more heat once the building is occupied.
bluGill 6y ago
Yes, because when the inside of the house is close to outside temperature the temperature difference is lower (obvious). Heat loss depends on temperature differential so there will be less energy lose. The real question you should ask isn't is it true - it is. The real question is it significant enough to worry about. If you are going to be gone for several days it is. If you are only talking about a part of a day though things are different, and get complex. If you heat with electric (including heat pumps!), keeping the house a consistent temperature makes you use an even amount of heat all day, and so your house can be better supplied by renewable energy. If many people turn the heat up when (or just before) they get home at 5pm - the renewable power available isn't enough and the power company will have to turn on fossil fuel plants to make up the difference. Thus you might use more energy but use a better type of energy by keeping the house warm. For many houses solar heating (from windows) is nearly enough to keep the house warm all day even on the coldest days, so it doesn't matter as the heating system isn't working anyway. Note that the previous two paragraphs contradict each other. I don't know how to work that out (for cooling it is a big deal), so you will need to ask questions - be prepared for different answers at different times. If your house is well insulated you shouldn't see much a change in temperature indoors, and as such there is only a tiny amount of energy save with setbacks. So why not just enjoy a comfortable temperature for the rare exceptions to your schedule? If your house is not well insulated, fixing that should be your priority. There are probably other factors I can't think of.
- elihu 6y ago
  > If you heat with electric (including heat pumps!), keeping the house a consistent temperature makes you use an even amount of heat all day, and so your house can be better supplied by renewable energy. If many people turn the heat up when (or just before) they get home at 5pm - the renewable power available isn't enough and the power company will have to turn on fossil fuel plants to make up the difference. It also depends on what kind of renewable. A lot of people set their thermostat lower at night, which aligns well with solar power, which is only available during the day. But turning it down during the day and turning it up in the evening doesn't align as well (especially in the winter when the sun goes down early).
outworlder 6y ago
The answer is complicated. For the same amount of insulation, the amount of heat lost is also dependent on temperature. Leaving the house at a lower temperature (but still heated, not off!) while you are absent for long periods of time _usually_ is a better approach. Because you are losing heat anyway, the question is just how much. Sure, if you have really amazing insulation(outside of specially engineered buildings you probably don't), the difference may not be significant and you would be right.

cmrx64 6y ago

> It takes a lot of energy to raise the temperature of a house - more than to maintain a given temperature is this true? the house is constantly bleeding off its heat at a rate proportional to the temperature difference between interior and exterior. it should always cost more energy to maintain the higher temperature gradient than to just let the heat bleed off (which it was always going to do) and add in more heat once the building is occupied.

bluGill 6y ago

Yes, because when the inside of the house is close to outside temperature the temperature difference is lower (obvious). Heat loss depends on temperature differential so there will be less energy lose. The real question you should ask isn't is it true - it is. The real question is it significant enough to worry about. If you are going to be gone for several days it is. If you are only talking about a part of a day though things are different, and get complex. If you heat with electric (including heat pumps!), keeping the house a consistent temperature makes you use an even amount of heat all day, and so your house can be better supplied by renewable energy. If many people turn the heat up when (or just before) they get home at 5pm - the renewable power available isn't enough and the power company will have to turn on fossil fuel plants to make up the difference. Thus you might use more energy but use a better type of energy by keeping the house warm. For many houses solar heating (from windows) is nearly enough to keep the house warm all day even on the coldest days, so it doesn't matter as the heating system isn't working anyway. Note that the previous two paragraphs contradict each other. I don't know how to work that out (for cooling it is a big deal), so you will need to ask questions - be prepared for different answers at different times. If your house is well insulated you shouldn't see much a change in temperature indoors, and as such there is only a tiny amount of energy save with setbacks. So why not just enjoy a comfortable temperature for the rare exceptions to your schedule? If your house is not well insulated, fixing that should be your priority. There are probably other factors I can't think of.

elihu 6y ago
> If you heat with electric (including heat pumps!), keeping the house a consistent temperature makes you use an even amount of heat all day, and so your house can be better supplied by renewable energy. If many people turn the heat up when (or just before) they get home at 5pm - the renewable power available isn't enough and the power company will have to turn on fossil fuel plants to make up the difference. It also depends on what kind of renewable. A lot of people set their thermostat lower at night, which aligns well with solar power, which is only available during the day. But turning it down during the day and turning it up in the evening doesn't align as well (especially in the winter when the sun goes down early).

outworlder 6y ago

The answer is complicated. For the same amount of insulation, the amount of heat lost is also dependent on temperature. Leaving the house at a lower temperature (but still heated, not off!) while you are absent for long periods of time _usually_ is a better approach. Because you are losing heat anyway, the question is just how much. Sure, if you have really amazing insulation(outside of specially engineered buildings you probably don't), the difference may not be significant and you would be right.