Where to set the thermostat?

[saichele]

As an accomplished cheapskate, anytime I'm running the furnace (the heatpump in this case) I've always kept the thermostat as low as I could stand - 63F, on the theory that it costs more to keep the house 68 than 63.

This wasn't much of an issue in MI, because it rapidly got cold enough to crank the woodstove. But here in central PA we've had a lot more tepid days - highs inthe 40s, lows around freezing, so a lot more running the heatpump.

Now, the heat pump kicks on anytime the room temp drops more than 0.5F below the set temp, and kicks off at 1F above, so we're dealing with a small range.

So where I'm going is - would it take more energy to raise the house temp from 67 to 68 than from 62 to 63? It seems like actually maybe not. Similarly, although there's a slightly higher gradient (38F instead of 33F) across the R13 in the walls, it seems like the change in flux can't be that big.

So should I turn up the thermostat, or should I keep it low because it builds character?

Thanks
Steve

 

[begreen]

We have a long shoulder season out here. Our heatpump has a digital thermostat that is set to 65 at night and 69 during the day when we're active and 70 during the evening. When daytime temps drop below 45-47º we are burning 24/7 and heating with the wood stove.

 

[EatenByLimestone]

Heat is always going to transfer to the cooler area. It's going to transfer faster the greater the temperature difference is.

If the outside is 62 degrees, the outside and inside are the same and heat is not transferring in or out. its not going to take much to move the temperature to 63 degrees inside. But as soon as the inside raises above the outside, heat is going to want to travel to the cooler outside.

If the outside is 62, and the inside is 67, you're going to have to overcome the heat lost to the outside plus additional heat to pop the temp up to 68.


I'm not sure if that came through clear or not.

 

[EatenByLimestone]

Should you keep the temp low? That's for your wife to answer! I've been married long enough to know my answer is wrong! Lol

 

[saichele]

Maybe I just need to think differently about it - the house in MI was also 100+ yrs old, and porous. we lost a lot to convection in addition to conduction through the walls lined with crumpled paper. So any heat we made passed out of the house pretty quickly.

The current house is tight - if the range hood is going to much we get chimney smell in the living room. So we're not losing much to convection, and we have decent modern insulation. Maybe it's OK to keep it 66 or 67 when it's in the 30s outside.

 

[EatenByLimestone]

Sounds like you'll lose a lot less heat with the new place.

 

[Where2]

If you're most likely worried about the "end of the month" effect, you could read your electric meter, set the thermostat one way, read the electric meter in a day or two, and make your determination whether it will be sustainable long term.

I've tried to heat a 1960's sieve with electric, it's a kicker at the end of the month. The worst day were the days the wind was blowing and my $$$ was basically blowing out the walls, old windows, the doors and every other opening. Air sealing did wonders...

 

[semipro]

Keep in mind too that most thermostats for heat pumps typically engage "emergency" (electrical resistance) heating if the set temp differs from the room temp by more than a few degrees which really bumps electrical usage. If your setback practices result in the use of resistance heat then you've certainly lost any potential gains of setting back.
I've actually disabled the emergency heat on our system with a switch at the air handler so that I can enable it in a real emergency.

 

[Dobish]

with a drafty house, I noticed that the furnace kicks on a lot more when set to 67 than 66. When it is set at 62 (for nighttime) it doesn't kick on unless it is really cold out (less than 20º outside). It takes about 10 minutes to warm up to 66 at 8am, and then the fire gets stoked and the furnace doesn't kick on again for the rest of the day.

When i had it set at 65 at night, it would kick in every hour or so...

in theory, if your house is sealed, the amount of energy needed will be the same between 62 and 63, and 67 to 68. A joule is a joule.

 

[semipro]

in theory, if your house is sealed, the amount of energy needed will be the same between 62 and 63, and 67 to 68. A joule is a joule.

True if there's zero heat leakage from the house but then why would you need a heater? Also assuming there are no materials in your house undergoing a phase change between 62 and 68 (sorry, couldn't help tossing that out there)
The fact that temp differential drives heat flow is why turning down your thermostat set temp at night decreases energy use.