Balance point
thermal balance point · heat pump balance point
A heat pump's balance point is the outdoor temperature at which its heating output equals the home's heat loss; below it, the heat pump alone cannot keep the home at the set temperature.
A home loses more heat the colder it is outside, while an air-source heat pump delivers less. Plot both against outdoor temperature and the two lines cross. That crossing is the balance point.
Where it falls depends on how the system was sized. DOE’s Building America guidance describes a range from about 40 °F (4 °C), for a heat pump sized to the cooling load, down to −15 °F (−26 °C) or colder, for a cold-climate unit sized to the full heating load at the local design temperature.
Below the balance point another source supplies the difference: auxiliary heat strips in the air handler, or a furnace in a dual-fuel system.
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