[nitsuaeekcm]

The best mental model for a heat pump is that they can maintain a certain temperature differential, say 80F. If it gets to be 0F outside and you want it to be 70? You don’t need to switch to a fully separate heating system, you just need to warm up either the incoming or outgoing air an additional 10 degrees via a small resistance heater. The super wide range heat pump systems will do that automatically, and the principle really applies to any differential you could want.

[JadeNB]

> The best mental model for a heat pump is that they can maintain a certain temperature differential, say 80F. If it gets to be 0F outside and you want it to be 70? You don’t need to switch to a fully separate heating system, you just need to warm up either the incoming or outgoing air an additional 10 degrees via a small resistance heater.

Are your 70 and 80 switched? What you describe doesn't sound like it needs any addition.

[VBprogrammer]

The wide range ones are basically two heat pumps back to back using different working fluids. They should only be used in applications where they are really required as there are obviously impacts to the COP.