Is it better to leave the heat pump on overnight, yes, it is better to leave heat pump on overnight at constant temperature rather than turning off and on, because heat pumps are most efficient when running steadily and turning off causes expensive backup heat to turn on. Heat pumps including Trane XV20i, Carrier Infinity 20, and Goodman GSZC16 work by moving heat, not making heat, with efficiency measured by COP of 3 to 4 at moderate temperatures, meaning 3 to 4 units heat for 1 unit electricity. If you turn heat pump off at night and house cools from 70 to 60 degrees, in morning heat pump must recover 10 degrees, which causes thermostat to call for auxiliary electric heat strips at 3 to 10 kW that cost 3 times more than heat pump, using 10 to 15 kWh extra costing 1.50 to 2.50 dollars per recovery, whereas leaving on overnight at 68 degrees uses only 3 to 5 kWh costing 0.50 to 0.80 dollars. Also, heat pumps have variable speed compressors that run low and efficient to maintain temperature, turning off forces high stage. Best practice is set back temperature only 2 to 3 degrees overnight, not 10 degrees, to avoid aux heat. For example, set 70 day and 68 night. Programmable thermostat should be set to heat pump mode that locks out aux heat unless temperature difference more than 3 degrees. Leaving on overnight also maintains better humidity control at 45 to 50 percent and comfort. So leave heat pump on overnight, only set back 2 to 3 degrees.
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