I use a Janitrol (I know, thin coils, etc.) heat pump to supplement my
gas furnace in Minnesota. I've had it for twelve years now and haven't
had a problem with it yet... It uses a outdoor thermostat located in
the condenser to cut out the hp to the furnace. I set it at 33
degrees, below that the hp will run too long, imo. Of course being in
the middle of Winter here in the North, it isn't being used at all. We
have had some warm winters though when I have used it on/off all
winter. I wouldn't have it at all if were not for the off-peak
electric rate I receive, it was just raised to 3.8 cents per
killowatt/hr. The first increase in electric since I have lived here.
(12 yrs)
I run the air in the summer as much as I want, very inexpensive when
using the hp in that way. They also let me wire my furnace into the
off-peak meter so all the electricity consumed by it is at the low
rate. btw, the normal rate is 7.8 cent per Kwh.