Been lurking here for over a decade, fascinating board.
So for my first question here:
Live it Montreal, winters go down to -25F for a few days. I have an 11 year old contractor grade 3.5T Ruud 11 SEER heat pump (performed flawlessly all these years except for leaking reset valve that was fixed this year) with resistance heat backup, and a Honeywell Prestige touch-color thermostat with outdoor stat (love that thing!). 3000SFT house.
I have set the stat aux lockout to 24F outdoor, and heat-pump heats house fine enough with no expensive resistance AUX down to that.
However the heat-pump lockout on the thermostat can only be set to 4F outdoor at the lowest, or never lockout beyond that. At 4F my heat pump can still produce a delta T of 12F. Wish Honeywell allowed a lower setting!!!
Have read conflicting info:
1) Dont bother running heat pump below freezing (I think this mainly pertains to fuel backup, not for expensive resistance backup).
2) Dont bother running heat pump below 0F, as it will only produce negligible heat and cold drafts.
3) Never turn off heat-pump, since COP is always greater than 1 (then there are theories of defrost cycle killing efficiency, and beating your heat pump to death running it indefinitely)
Original installer just said to switch it to emergency heat on the coldest days, if I want to do the equipment a favour.
What do you all say? Set it to lockout at 4F, or let her run forever?
(I dont mind "cold blow" too much, want to save electricity if I can, and don't want to have to get a new compressor any time soon!)