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Tapiotar
11-07-2007, 07:36 AM
Now that it's getting cold again, I'd like to talk thermostat settings. Right now, I've got it set for 58 F at night, and 65 F during the day. When it gets bitterly cold out, (that is, sub-zero to 20's F) I'll probably turn it up to 67 F when I'm home, and 60F overnight and when I'm out. I read in some energy publication (don't remember where, so I can't cite) that you waste more energy trying to rewarm the place if there is more than a 5 degree difference in day and night temperature. Anyone know?

Where do you set your thermostats in winter?

Napier
11-07-2007, 11:37 AM
It doesn't take any energy to go back and forth between two temperatures. The thing you're heating absorbs heat when you heat it and releases heat when you cool it. It has to absorb and release the same amount of heat. More specifically, the heat content is a state variable that is independent of the path you follow to get there.

A first order approximation of the energy it takes to heat your house for a year would be adding up, for every second of the year, the temperature difference between the inside of your house and the outside. So, whenever you turn the thermostat down, you need less heat to heat the house.

It's a more complicated question whether it's worth doing, which depends on how much your trouble is worth, and also depends on higher-order issues like whether the efficiency of your heating system is independent of all the other variables.

I think you should figure your dollars-per-hour to heat the house is proportional to the temperature difference inside versus outside, and figure the house temperature changes in a small enough fraction of a day that you can pretend turning the thermostat down for 12 hours means lowering the difference for 12 hours (I bet this would be way wrong for just 1 hour but pretty correct for more than 5 or 10). Estimate what you're spending in dollars per hour for tomorrow, and see how much less it would be if you reduced that difference. That's what you should expect changing the thermostat to save you.

USCDiver
11-07-2007, 12:21 PM
Now that it's getting cold again, I'd like to talk thermostat settings. Right now, I've got it set for 58 F at night, and 65 F during the day. When it gets bitterly cold out, (that is, sub-zero to 20's F) I'll probably turn it up to 67 F when I'm home, and 60F overnight and when I'm out. I read in some energy publication (don't remember where, so I can't cite) that you waste more energy trying to rewarm the place if there is more than a 5 degree difference in day and night temperature. Anyone know?

Where do you set your thermostats in winter?

How come if your house is comfortable for you at 58F now, it won't be comfortable at 58F later in the winter?

control-z
11-07-2007, 12:55 PM
Depends on your heat source. I have a big heat pump. My thermostat stays on 72 or so all the time. Can't say I wouldn't mind saving some money though, I've just always felt that letting the house get cold just makes the heat pump have to work longer to get it back to 72.

Chefguy
11-07-2007, 02:10 PM
It also depends on how well-constructed your house is. Mine leaks somewhat, so I need to set at a higher temp. In winter, it's at 72 when we're home, set back to 68 during the day and at night. Any lower than that when it's below 20 degrees and we'll have a frozen heat loop.

gigi
11-07-2007, 04:22 PM
Thank your for asking, and I hope you don't mind if I glom on with a question. A friend tells me that if I leave my thermostat at 55 during the coldest months, my pipes will freeze. The only time I've had this issue was when the furnace actually died and the house was much colder than that. Should 55 be sufficient? The kitchen and bath are not on outside walls, but there are some larger pipes running along the cellar walls. Not sure what they are.

Roland Orzabal
11-07-2007, 04:36 PM
I don't have a thermostat. My apartment has a motel-style AC/heater unit. I turn it on when ice begins to form on the inside of my windows, so that I do not die during the night. Beyond that, I'll take it as cold as I can get it.

(Bear in mind that I live in Southern VA; it really doesn't get all that cold here in the first place.)

Chefguy
11-07-2007, 06:11 PM
Thank your for asking, and I hope you don't mind if I glom on with a question. A friend tells me that if I leave my thermostat at 55 during the coldest months, my pipes will freeze. The only time I've had this issue was when the furnace actually died and the house was much colder than that. Should 55 be sufficient? The kitchen and bath are not on outside walls, but there are some larger pipes running along the cellar walls. Not sure what they are.

Again, it's a factor of insulation. In our place, part of the living room heat loop passed in front of the front door and was unprotected from the elements. I had the t-stat set at 65, and the pipe froze as soon as the t-stat quit calling for heat. Properly insulated, there wouldn't have been a problem.

Tapiotar
11-07-2007, 06:31 PM
How come if your house is comfortable for you at 58F now, it won't be comfortable at 58F later in the winter?

The thermostat is placed on an interior wall, probably the warmest place in the whole house. When it is bitterly cold outside, say around 10 degrees F, exterior walls and windows get very, very very cold, and places in between are also rather chilly. So if the temperature by the thermostat is 58, for example, the temperature by the couch or in my bedroom would be 53 or 52 F. Those five degrees make a big difference.

Tapiotar
11-07-2007, 06:34 PM
Thank your for asking, and I hope you don't mind if I glom on with a question. A friend tells me that if I leave my thermostat at 55 during the coldest months, my pipes will freeze. The only time I've had this issue was when the furnace actually died and the house was much colder than that. Should 55 be sufficient? The kitchen and bath are not on outside walls, but there are some larger pipes running along the cellar walls. Not sure what they are.

Depends on the insulation near your pipes. I know people who leave their thermostat at 55, and even when it's ten below zero outdoors, the pipes are in no danger. But it is a brick house that holds heat well. When I lived in Minnesota, and the temps were getting colder than 20 below, I'd usually have a trickle of water running in all the taps, as recommended, to prevent freezing.

But you can buy foam tubes to put around pipes at most hardware stores.

gigi
11-08-2007, 08:09 AM
But you can buy foam tubes to put around pipes at most hardware stores.OK, cool. I'll have to investigate just what's on the exterior walls. I don't pay for water but I hate to leave it running and have my landlords paying.