Water-source heat pumps
A water-source heat pump uses water — a building loop, well, or pond — instead of air to exchange heat, for high, steady efficiency.
How a water-source heat pump works
Instead of outdoor air, a water-source heat pump exchanges heat with a water loop — a circulating building loop (common in apartments and commercial buildings), a well (open-loop), or a pond/lake. Because water holds a more stable temperature than air, efficiency stays high and consistent year-round.
Water-source vs geothermal
Geothermal (ground-source) is technically a type of water-source system that uses buried ground loops. The term "water-source" usually refers to systems on a shared building water loop or an open-water source (well/pond). Both reach high COPs (3–5) and avoid the cold-weather capacity drop of air-source units. See our geothermal guide.
Cost and best uses
For a shared building loop (multifamily/commercial), per-unit equipment is relatively affordable; for an open-loop well or pond system, cost depends on the water source and runs into the tens of thousands like geothermal. They suit buildings with an existing water loop and homes with a suitable well or pond.
Frequently asked questions
What is a water-source heat pump?
One that exchanges heat with a water loop — a building loop, well, or pond — instead of outdoor air, for high, stable efficiency.
Is a water-source heat pump the same as geothermal?
Geothermal (ground-source) is a type of water-source system using buried loops. "Water-source" more often means a building water loop or open-water (well/pond) source.
Are water-source heat pumps efficient?
Yes — because water temperature is stable, they reach high COPs (3–5) and avoid the cold-weather capacity loss of air-source units.
Related
Sources & further reading
Educational guide, reviewed against US DOE & ENERGY STAR guidance and updated June 2026. Estimates only — not a substitute for a professional assessment or Manual J load calculation.