Quote:
Originally Posted by AC_Hacker
Mikesolar,
Are you stating this as applying to ALL heat pump situations (mini-splits are heat pumps, too) or are you referring to high-mass radiating systems?
Reason being, I am currently using an ASHP to heat my house, 9,000 BTU mini-split, with a built-in set back feature, and there is no problem what so ever.
-AC
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A heat pump is, by its very nature, almost always undersized for the job (to some extent). This is why we have the backup heat installed.
The amount heat needed to raise a slab (it can be low mass as well) is considerably more than that needed to keep it a degree or so from the setpoint. We are wanting to have a system respond quickly when asked and the HP is not as capable of it compared to a gas boiler.
It is all about expectation. If you don't mind using the straight electric or gas backup to do the fast injection of heat, then you can use the setback but if not, I would not because it will take a long time to heat up with just the HP, especially when it is colder out and heat load is closer to the HP capacity.