Heat pump is not designed to be very effective in temps below 55 degrees. In OK. it looks like some days get above 55 (not all of them), but at night it appears to not even be close. When it gets below 55 degrees I go to the LP furnace.
FWIW, when using my heat pump or A/C unit, I get little to no freeze up using the A/C in the summer at or above 78 degrees or the heat pump in fall at or above 55 degrees.
Computers manufactured by companies such as IBM, Compaq and millions of others are by far the most popular with about 70 million machines in use worldwide. Macintosh fans note that cockroaches are far more numerous than humans and that numbers alone do not denote a higher life form. -NY Times 11/91