Trying to figure out heat...does this make sense?

Your looking at it in the right direction, but your method of calculation isn't correct.

The first thing to realize is that heat always runs "downhill" from hot materials to cold ones. and the way to look at it is that the amount of "juice" as you put it, is basically delta-T (the difference in inside and outsided temperatures) times a factor for whatever "thermal resistance" the heat flows through, in your case, that's the insulation of the walls, roof and windows of your dwelling. Winds outside come into it too, as a second order effect.

And yes, all other things being equal it does take "more juice" the get to 72 than to 70, and more to keep it at 72 than at 70, when the outside temperature is below 70.

The simplest and most efficient way to do what you are talking about is to set the heat as low as you can when you're not home, as long as you don't run into the possibility of freezing plumbing, and then turn it up to 72 or whatever you want when you return. That's providing you don't mind whatever waiting time your heating system takes to raise the temperature to where you get comfortable. If you can't tolerate the wait, then set your "not home" temperature a little higher.

You might also want to consider going a little higher tech and using a timed thermostat set to raise the temperature a bit before your expected return, or use some of the whiz-bang gadgetry that lets you control stuff like that with a telephone call.

Happy Holidays,

Jeff

The more inefficient that your system is, the more "juice" it takes to get to 70 degrees. No need to set the thermostt higher.

Your away temperature of 68 degrees is way too high! Mine is 48 degrees.

Yes. The new way uses slightly less heat.

Nick

Thanks to Jeff for the detailed explanation...I will look to a prgrammable thermo -

Scott, my system is inefficient because one of my big radiators is not getting too hot. I think its a valve issue, so to get the house confortable, It has to go to 72.

I have a 18 year old cat in the house - don't want a catcicle when I get home. Maybe I will drop it to 62 and see how that goes.

Bluesman

Maybe you can buy the cat a fur coat.

We drop it to 45 and our cat Darwin hasn't said he minds it at all. I'm hoping it'll help burn some of the fat off of him.

He's gotten so rotund that he can't run as fast as the mice anymore, so he's mechanized the process:

Happy Holidays,

Jeff

The wind outside is a major factor in the amount of heat loss.

Setting the thermostat and actual temperature are different things. Why do you have to set it higher to feel the same? The thermostat is a switch. The heater is either off or on. If it is running and brings the heat high enough to trip the switch, that is what counts. Other factors are at work here. It may be easier to fix that problem.

Yes, you have the right idea. That is similar to the "degree days" the oil companies use to determine when to deliver to you. IIRC, they use the differential between actual temperature and 60 degrees.

You have to think about temperature differential. The greater the differential, the greater the loss.

You can increase comfort by adding a humidifier, cutting down drafts that create heat loss, add insulation. If it has been a long time since you've done any of that, do a quick review to see if there have been any changes. Ed

I just remembered I should have mentioned that if getting a timed thermostat and installing it is too big a hassle you can jury rig one easily.

Just get an inexpensive plug-in-the wall light timer and connect a small lamp bulb, like a nightlite bulb, to it on a length of cord.

Let the timer light the bulb when you want the temperature to be lower. Experiment with locating that bulb on the wall below the thermostat. You'll find a location where the rising heat from the bulb will "fool" the thermostat into thinking the room temperature is higher than it really is and thus "push the heat down" the amount you want.

A "red-neck" solution, but one which works quite well.

Happy Holidays,

Jeff

I think it might already have one.

Holy s*it! My cat's name is F***ss, but that thing is a monster!

It actually looks like it's been touched up to make the cat look huge! Bluesman

Now that is some ghetto thermo rigging...but it makes me wonder - the xmas tree is within a few feet of the thermo - perhaps that is making the house cold at night when the tree is lit..

hmm....

Bluesman

On 12/20/2004 2:40 PM US(ET), Jeff Wisnia took fingers to keys, and=20 typed the following:

Was 6=BA F (-14 C) here in NY this morning.

Honest injun it's not unretouched. It's mostly hair. He was at the vet's for his annual rabies shot last month and weighed in at only 12.5 lbs, down half a pound from the year before.

Jeff

Well, X10 makes a "thermostat setback" gadget which works on the same principle I described, nly it has an adjustable power level so you don't have to move it up and down on the wall to adjust the number of degrees of setback. Here's one now:

Happy Holidays,

Jeff

Put a heating pad on the bottom of the cat house. Small electric charge vs. big heat bill. Also when you go to sleep turn the heat down and use an electric blanket. Have your programmable thermostat fire up the heat a half an hour before you get up.

The cat that used to own me would complain bitterly about the cold every fall for about three days. Then he would start eating about twice as much dry cat food and stop complaining.

Now, this is an interesting subject. First, the actual temp isn't really 68 or 72, cause the actual zero is about -450, where the mollecules stop jiggling.

Your furnace runs just enough to replace the heat that is lost to the outside. If you lose some ammount of heat, the furnace replace it.

Heat loss depends on a couple things. Air loss (drafts) and conduction through the walls, ceiling, etc.

If it's colder outside, the air leaking in is colder. And the delta T (difference in temperatures from inside to outside) is higher.

Anyhow, if you turn your thermostat down it saves you money. Because the delta T is lower. And also the air that leaks out isn't quite as hot (and you didn't pay to heat it up hotter).

If you don't feel warm enough during the winter, get a humidifier.

Good point. My away temp is 58.