Heat Pumps and Electric Heating - Outside temp and 2nd stage heat

Assuming the following:

- the heat pump is the right size for the house and is working properly
- the house is well-insulated
- the thermostat is set at about 68 degrees

Question: At what ouside temps can the heat pump maintain inside temp without using the auxiliary heat? Or, to put it another way, approximately how far can the outside temp drop before the unit *has* to kick in the second stage in order to satisfy the thermostat?

Thanks.

At 32º the condensation on the outdoor unit will begin to freeze and you will occasionally go into defrost and the aux will kick in there. As the temp drops below that you continuously loose efficiency and the aux will be used progressively more to keep up. It's just about impossible to give exact numbers or even ballpark numbers because alot of factors come into play. How well the system has been maintained, installed to the heat loss of your house will dictate how efficient your h/p will operate at cold temps. I've seen some h/p's that are not worth a dime once they get below 30º and I've seen others chug along pretty good down into the teens.

Matts got it all there, just like to add. Even how the wind blows at are around the home makes a lot of differences . In when the strips will kick in. From time to time go feel the big copper line as to how hot are warm it is there at the indoor coil.

ED ;)

Aux. heaters will also kick in when temps drop too fast outside. Also heaters will also cut in when the sun goes down and visa versa keep them off when the sun comes out.