According to Beach Trading Company :
On Feb 1, 8:32*am, bill wrote:
Bill,
2) Heat pumps work best when maintaining a constant set point (i.e. no
drastic set point changes or night setback).

Thanks for answering my piece of the question. I called the company
that installed my heat pump yesterday and they recommended that I not
set back more than 5 degrees. The aux heat strips automatically kick
in if the temps need to be raised more than 3 degrees and more strips
run the longer the unit is working to raise the temps. Based on that
I've set the overnight temps to drop 2 degrees and I'll see how that
works. I'm in SC and Feb is typically the highest wintertime usage so
it will be interesting to see the impact of having a more constant
temp.

Note that there are some programmable thermostats that "understand"
heat pumps. There are some that are smart enough to bring the temperature
back up from the set back in increments of a few degrees at a time,
so the HP never thinks it's gotten too far behind. There are others
that "know" that the abrupt temperature discrepency (between room temperature
and setpoint) is due to their "returning from setback", inhibit backup
heat, and force the HP do do all the work. The latter have to be built
into the HP I believe.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.