Answer
Apr 07, 2026 - 12:35 PM
The "20 degree rule" for heat pumps refers to the guideline that a heat pump operates most efficiently when the temperature difference between the indoor set point and the outdoor air is no more than 20°F (about 11°C). If the difference exceeds 20°F, the heat pump's efficiency drops significantly, and supplemental heating may be needed to maintain comfort.
