From Air to Water to Warmth

A newer type of heat pump is starting to show up in homes: the air-to-water (A2W) heat pump. Like the more common air-to-air heat pumps, it pulls heat from outdoor air. But instead of blowing warm air through ducts, it heats water and sends that water through radiators, radiant floor tubing, or other water-based heating systems (called hydronic heating). That makes it a good electric replacement for an old oil, gas, or propane boiler, especially in a house that already has radiators or in-floor heat.

Compared with air-to-air systems, A2W heat pumps run quieter and can heat different rooms or zones separately. They work best when the water they produce doesn't need to be very hot, since lower water temperatures mean better efficiency. That's easier to achieve in a well-insulated house or one with radiant floors than in an older home with small, high-temperature radiators built for a boiler.

The tradeoffs are cost and complexity. A2W systems generally cost more upfront than standard heat pumps, and fitting one into an older house with existing hydronic heat can take careful planning, sometimes including upgrades to the radiators or distribution piping. If your house is heated by a boiler and radiators or radiant floors, this is a technology worth knowing about as an option when that boiler eventually needs replacing.