Balance point (heat pump)
The outdoor temperature below which a heat pump alone can't keep up with a home's heat loss, so backup heat — electric strips or a gas furnace — has to take over.
A heat pump's heating output falls as the outdoor temperature drops, because there's less ambient heat to extract from the outside air. The balance point is the temperature where the heat pump's falling output exactly matches the house's heat loss; below it, backup heat is needed to keep up. Standard heat pumps typically start leaning on backup somewhere in the mid-20s to mid-30s°F; modern cold-climate models hold meaningful output down to roughly −5°F and are rated to operate to about −13°F.
What happens at the balance point depends on the system: an all-electric heat pump switches to electric-resistance strips (expensive heat), while a dual-fuel system switches to a gas furnace instead. Our calculator flags a "cold-climate" heat pump automatically when a home's heating load runs more than 1.6× its cooling load, and prices the roughly 15% equipment premium that goes with it.