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Need an expert statement
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jmelson:
An air-backed heat pump will certainly not work well at -15C without using electric resistance heating.  Does the air handler (indoor) unit have this?  Is the electric resistance element properly sized for the load?  It will likely need to be pretty large for a typical home at that outside temp.  Somewhere around 10 - 20 KW is likely the minimum requirement.
Jon
Siwastaja:

--- Quote from: jmelson on February 13, 2022, 03:00:37 am ---An air-backed heat pump will certainly not work well at -15C without using electric resistance heating.

--- End quote ---

This is just BS.

Modern models work really well at -15degC. Doesn't even need to be that modern. State-of-the-art machines 20 years ago could already do it.

With indoor fan set at maximum to provide lowest possible condensation temperature, COP can even exceed 2.0 in a well designed machine! It's still far from resistive heating.

-25degC is a different story. Many products continue operating even to -35degC, but COP reaches 1.0 even before that, equivalent to resistive heating, in which case it's a matter of taste whether you turn it off to "save on operating hours" (but keep wasting some 50W in compressor heater), or keep it running.
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