[onphonenow]

The key issue is despite claims that cold doesn’t affect heat pumps it absolutely does. We have an old house. When very cold the heat pump struggles to put out enough heat. It works well enough, but something to be aware off - go bigger in system than you think you need maybe

[VLM]

"go bigger" will result in short cycling during the hot summer resulting in high humidity and mold problems in the summer.

[PaulDavisThe1st]

Untrue. All modern heat pump systems use DC motors ("inverter technology") and will run continuously at variable speed until target temperatures are exceeded by a (programmable) margin. They do not turn on and off and on and off.

[tootie]

Nobody says that it has no effect. Only that efficiency decreases. And that even at diminished efficiency it's still better than a boiler.