House heating
April 8, 2004 7:13 PM   Subscribe

A question about heating a household: Do you expend more energy maintaining a constant temperature in a house, or does it cost more letting the thermostat become lower and heating the house to a normal temperature when it is necessary?

I have a thermometer that adjusts the temperature up or down depending on the time of the day. When I'm at work and it is winter, I set the temperature lower then when I am at home. Have I wasted my money on this thermometer? When I let the temperature slide, the furnace could run for 15 minutes to 'catch up' for the heat lost throughout the day.

(yes... I'm still heating the house at this time of the year)
posted by sleslie to Home & Garden (9 answers total)
This thread might be useful.
posted by BlueTrain at 7:32 PM on April 8, 2004

This page from the US dept of energy says:

A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature.

In other words, lowering it is a good idea.
posted by vacapinta at 7:43 PM on April 8, 2004

I dunno about a house, but I know for a good-sized outdoor spa, my family saved money by letting it cool down at night and then heating up in the afternoon versus keepin it high all the time.
posted by jmd82 at 10:09 PM on April 8, 2004

While it's not exactly rigorous, you can think of it this way: it you left the thermostat up for the, let's say, ten hours you're gone during the day, would the furnace be on for more than fifteen minutes, total? Almost certainly yes. The fifteen minutes the furnace is on when you raise the thermostat is less than the time the furnace would be on to keep your house warm throughout the day.
posted by DevilsAdvocate at 10:20 PM on April 8, 2004

you can buy the thermostats that can be programmed to heat/cool your house differently at different times of the day according to your needs. I understand that this is more expensive than the "moving it yourself method" but when I am doing this I tend to forget every now and then. I don't have one, but I like the idea of it. I would set the thermostat to kick in ~15 minutes before I got home so that it would be nice and toasty/cool when I arrived.
posted by busboy789 at 5:03 AM on April 9, 2004

the more times you fire up your furnace, the more times you use more fuel in ramping it up to full efficiency.

increase the differential on your stats to as far as you can handle (eg. stops at 25 and comes on again at 20 rather than stop at 25 and come on again at 24) this reduces the amount of 'hunting' that is carried out by the system to maintain set temperatures.

when you are out, turn your heating off.
posted by Frasermoo at 10:56 AM on April 9, 2004

Assuming the efficiency of your furnace is independent of the room temperature (is this true?), simple physics has the answer: The amount of heat radiated by your house is proportional to the difference in heat between inside and outside. So, you want to minimise the difference between inside and outside temperature (multiplied by the time that is the temperature difference). This means that if you let the house get cold when you're not there, the house radiates less heat during that time, which means that's less heat you have to put back in the house later.
posted by fvw at 11:28 AM on April 9, 2004

Response by poster: when you are out, turn your heating off.


This is less argumentive (I realize that your climate isn't as cold as mine!) and more informative, but you can't do that if the temperature outside is below freezing, as you run the risk of having the water inside the house's plumbing freezing, bursting, and then flooding the house!
posted by sleslie at 1:56 PM on April 9, 2004

then turn your heating down as far as the situation will allow when your not there.
posted by Frasermoo at 2:25 AM on April 10, 2004

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