Question Regarding Dual Fuel Heating: Heat Pump and Propane Furnace

[mmc45414]

What really prolongs the life is cleaning the coils bi yearly. At least thats what I was told.

That sure makes sense also, because that would make the compressor run less as well. Seems like the compressor is always under the same PSI load, regardless of weather, and it is only going to revolve so many times, and the lower the temperature the more times it need to revolve to keep up. So if I had the option I would spend extra on propane if it prolonged the lifespan of the expensive heat pump. Especially at my age I may not outlast the next heat pump...

[Norville]

1 gallon of propane has 27-28 kWh of energy, so at $3/gallon your propane costs about $0.11 per kWh

At 10°F, your heat pump is 2.7x more efficient than propane, so electricity needs to cost you over $0.30 per kWh for propane to be cheaper.

But, demand increases as your home loses heat faster at low temperatures. There is a thermal balance point and an economic one. I agree that on propane the economic one is never achieved. Natural gas usually a different story.

My heat pump is good down to about 9 or 10 degrees, after which it starts to lag and my furnace will be called up (as auxiliary heat). Then it switches back to the pump without me ever having to do anything.

Depends on where they set the crossover point. I know they set mine low.

The other thing is that if the pump struggles and the indoor temp drops a couple / three degrees below where you set the thermostat, it will automatically switch even if above the crossover point temp setting.

The smart thermostat at work. The right way to do it is to estimate your heat loss, there’s an ASHRAE manual or some on line calculators. Then plot this vs the efficiency of your heat pump at various temperatures from the AHRI certificate. The state of Vermont has a nice spreadsheet to do this for you. The lines form an X, and where they intersect is the appropriate balance point. Mine was 28 degrees, so I set the balance point at 30. The heating contractor set it at 40, which is ridiculous.

My heat pump is an Energy Star “Cold Climate “ model, but no way can it keep up in near zero temperatures.