I saw today, for the first time ever, a heat pump that used a normal gas furnace for its auxiliary heat. I have never heard of this, but can’t think of why it might be a problem. Does anyone know of any problem with this type of set up?
None. It’s fairly common these days.
There should be a “fossil fuel” kit installed, usually on the side of the cabinet. This kit contains a time-delay relay to allow the heat exchanger to cool somewhat when changing from fossil fuel to the heat pump.
So, if you run the unit through its cycles, the heat pump will not fire immediately after using the gas furnace. Other than that its a regular system.