Home thermostats (house, heat pump, costs)

[AZ bound]

I'm looking for the right thermostat, and ran across this rule on the HD website,

A common misperception is that a furnace has to work harder to warm a house after the temperature has been set low during the day, eliminating any energy and cost savings. Studies have shown that the energy used to reheat the house is less than that used to maintain temperatures throughout the day at a higher setting, so you do actually save on energy costs by setting the temperature low at night and during the day while you’re away

With the factors here being cooling actually, and desert, is this rule thrown out the window? Should I keep the house a little cooler during the day when nobody is home?
What do you, who have been here for years do?

[ReadyFreddy]

I think they're saying DON'T keep the house cool when nobody's home. Re-cool it when you get home. Don't turn it completely off or anything but don't keep it at the usual (low) temp. That's what I do, and what the people I know do.

[HX_Guy]

Yes, most people will set the thermostat a little higher during the day and then turn it back down when they get home. Don't set it too high because then the AC will have to be on longer to cool things back down and that defeats the purpose. 2-4 degrees above what you would normally keep it at should be good.

You can also get a thermostat that can be set with your smartphone or via online then you could turn the temp down when you leave the office for example and have it be perfect in the house when you get home.

[Zippyman]

Originally Posted by AZ bound

I'm looking for the right thermostat, and ran across this rule on the HD website,


With the factors here being cooling actually, and desert, is this rule thrown out the window? Should I keep the house a little cooler during the day when nobody is home?
What do you, who have been here for years do?

Conventional wisdom doesn't take into account "time of day billing", which is very common here, and unheard of in most of the country. So if your house is on a time-of-day plan, and you can allow the home to "run wild" while you're not there (assuming those hours are "peak" billing hours), you will save money. That said, you will probably be fighting the "thermal mass" of your home if it is on a slab - which is common here, but rare in other parts of the country. If you let the temps rise when you're gone, the slab will heat up during the day, and keep giving off btu's while you're cooling the house down in the evening. So your a/c will run longer in the evenings - but that's still ok, because power is much less expensive then.

Fwiw, just to illustrate the point, my "time of use" electricity costs are about $.25 per kw from noon to 7 pm. I think "off peak" is closer to $.06 per kw hour. If I remember correctly, at 100 degrees outside air temp, my heat pump draws ~4kw when running. So it costs about a buck an hour "on peak", versus perhaps a quarter an hour "off peak". So no real worries if it ran all night to catch up - in the real world, it might only run an hour longer to get everything cooled off.

That said, I'm home during peak billing, and I just leave it where it is. The savings isn't worth suffering the heat for me.