An air-source heat pump is a single system that both heats and cools a home by moving heat rather than generating it. In summer it pulls heat out of the house like an air conditioner; in winter it runs the refrigerant cycle in reverse to pull heat from the outdoor air — even cold air holds usable heat — and deliver it inside. Because it moves heat instead of burning gas or running electric coils, the Department of Energy notes a heat pump can cut heating electricity use by roughly half compared with electric-resistance heat.
For an install, an air-source heat pump replaces both the air conditioner and the furnace with one outdoor unit paired to an indoor air handler or coil. That is the practical difference a buyer feels: a furnace-plus-AC replacement becomes a single heat-pump system. Ducted central models use the home's existing ductwork; ductless mini-splits are a separate ductless variant covered under their own category.
Two ratings describe the same unit. SEER2 scores seasonal cooling efficiency and HSPF2 scores seasonal heating efficiency; the federal minimum for a split-system heat pump is 14.3 SEER2 and 7.5 HSPF2 nationally. A quality install is less about chasing the highest rating than about correct sizing (a Manual J load calculation), a properly matched and AHRI-certified indoor/outdoor pair, and a sensible plan for the coldest days — either a cold-climate model or a backup-heat strategy below the system's balance point.