Essentially, they don't work well when the ambient temperature drops below 50 degrees fahrenheit. Lower than that, the energy required to extract heat takes more energy than using fossil fuels.
Personally, I have a heat pump/air conditioner, but I've never run it in heating mode. Instead, I use #2 heating oil and/or wood.
I have aversions to processes that use many energy conversions. Burning fuel to produce heat is pretty efficient. The process is simple too. Wood is great since it's renewable and direct. A heat pump is a very complicated process and requires converting electricity into mechanical processes which compress gases into liquids and then fans to move the heat into a room.
When the electrical grid fails, my wood stove still works just fine.
Only person I know of lives in a small apartment with a wall-mount heat pump that heats and cools. The apartments were originally resistive (electric) heat.
I asked him what happens when it gets to 0F like it does here often in the winter. He said "Resistive heat comes on, energy bill goes back to 200 a month."
And this is the gist of it all. Most of the time they are way more efficient, sometimes they revert to resistance heat. I’ve seen models be efficient down to near freezing, and some that will work at lower efficiency down another 10-20 degrees.
Yes. He said that it's amazing when it's like it is right now, 30+F outside, hot days are no problem for cooling. It's just those winter days that it has issues.
Yep all about heat sources and heat sinks
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