"Michael Baugh" wrote in message ...

Just visited someone with a heat pump, gotta question.
The outdoor temperature was in the 20's, I realize there
was precious little heat out there for it to relocate to inside.
So the strip heaters needed to be doing their thing. But when

There's actually a lot heat in the air in the 20's. Just not enough to
offset the heat loss from the house. I have a 2.5-ton unit that is
rated for 18000-19000 BTU at 17°, depending on the blower coil it's
matched with. Rated for 28000-29000 at 47°. I have R22 and understand
R410 does an even better job in bitter cold. Installers are
constrained in sizing because the units also handle A/C.

the thermostat would initially call for heat, the blower would come
on, and the heat pump would obviously be attempting to do its thing
first, rather than immediately kicking in the heaters. So the unit is
blowing cold air.

They tend to move more air, at a cooler temperature, than a furnace.
If the temperature at the register isn't above ambient then there's a
problem with the system.

Does a heat pump thermostat have a 2-stage sensor bulb, so that
when it gets colder in the house because the heat pump isn't finding
any heat out there, the heat strips get cut on? Or is there a time frame
that goes past before the strips get cut on?

Depends how it's set up and what the backup heat source is. Can be
time, temperature rise, outside temp, etc. They also use backup if and
when they defrost. My own system looks at the temperature of the air
coming off the blower and kicks the strips in if necessary.