Hvac peoples

I spent roughly 12 years doing mostly service, but some installs, on gas/ LP, 80% and 90%+ furnaces, heat pumps and AC, and a few oil furnaces.

Back then, the default setup for an air heat pump was an electric furnace, which provided backup/ emergency heat for when the pump could not keep up, and for defrost, or for when the heat pump failed.

A ground coupled pump, if you can afford it needs no defrost cycle, and very likely does not need backup heat. But you SHOULD have something in case the system failed

I don't care how "improved" heat pump tech is claimed to be, I doubt that in higher lattitudes (I'm in the N end of Idaho, 49 North) that it's improved enough to provide much better heat at lower temps than they used to, UNLESS you can go ground coupled.

The big problem with mating a gas/ oil/ combustion furnace to a heat pump is, you really must, in that case, put the heat pump BEFORE (upstream) of the combustion furnace, which is the opposite of how you want an AC/ furnace situation

This is to help prevent radical overheat of the pump during defrost, which the thing is essentially reversed into AC mode. It also prevents overheating the pump if you need additional heat because OD temps are low enough to need additional heat which the pump cannot provide.

You CAN put the indoor coil before the furnace, but it is highly recommended, and required in some areas (code) for an AC coil to be AFTER the furnace, to prevent heat exchanger rust/ corrosion problems.

Frankly I think the big hype over heat pumps by Bidumb and Trewdope is just that--hype and lies.

On a side not, it is not just low temps which establish the need for additional backup heat. It really is a combo of temp and humidity, known as enthalpy. Low temp dry air has very little heat value, and will cause less defrost problems, but will result in less pump heat output. Warmer, wetter OD, air, even though it has more heat content and will allow the pump to output more heat, will cause more icing and cause more defrost problems.

Deep snow areas MUST have the OD unit mounted on a stand to keep them up out of the snow, and high winds/ blowing snow/ sleet and low temp rain can also cause problems with outdoor coil icing.