To save on electricity bills I want to change to programmable thermostats. First try I bought the wrong kind - found out I have heat pump systems. I have a Robertshaw 9420 and a Trane 3AAT80B1A1. I don't know how to determine if they are multi-stage. Anyone know what kind of progammable thermostats I need?

If you have a heat pump a programmable thermostat will not save you much $$ in the heat mode since most heat pumps have to work hard just to maintain the temperature and when the temperature is not maintained the electric resistance heat comes on and that will really cost you. Our testing has indicated that unless you lock out the electric resistance heat with a set back thermostat on a heat pump you will actually use more power since when the thermostat comes out of set back it will activate the electric resistance just to bring the house up to temperature quickly.

Now if the electric resistance heat is locked out you might say so what now I am saving energy but the problem is in cold weather it might take hours or even a whole day to recover the 10 degrees set back without the electric resistance heat.

Heat pumps are marginal at best when the weather is real cold and most are set to lock out at 30-40 degrees. You might save a few bucks on the resistance heat end by the heat loss factor but always remember electric heat while expensive is 100% efficient so there is no stack/fossil fuel % of loss to deal with.

Everyone has a opinion and this is mine when it comes to set back T-stats on heat pumps.

Hvac1000 makes several very good points, as usual.

Just so we can give applicable advice, what is your backup/aux heat and what part of the country do you live in (ie what are yout winter temps like)?

I live in South Carolina on the coast. Great moderate weather but I hoped to lower the $150 increase in my electricity bill in a cold month. I don't know what my backup.aux heat is? How do I find that out?

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Originally Posted by bblalock

I live in south carolina on the coast. Great moderate weather but I hoped to lower the $150 increase in my electricity bill in a cold month. I don't know what my backup.aux heat is? How do I find that out?

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Your backup/auxiliary heat is the heat that comes on automatically when your HP cannot keep up. On your HP that's the heat that comes on when you manually switch to EMER. Most likely have a furnace using oil/NG/propane or you have heat strips in your air handler.

I know we don't have a furnace that uses oil or propane so it must be heat strips in the air handler. We have a one story house with two units - one for each side of the house. Hope this helps. So, do you think a programmable thermostat an option?