Hydronic heat pumps may be the most energy efficient type of electric central heat. Hydronic heat pumps use a refrigeration system to move heat from the earth or a body of water into the home during the heating season.
Hydronic heat-pump systems that get their heat from a body of water, such as a well or lake, are called open-loop systems because the system is open to the atmosphere. Closed-loop systems extract heat from the earth using closed loops of buried pipe. These closed loops recirculate the same water-antifreeze solution to move heat from the earth to the home.
Hydronic heat pumps, like air-source heat pumps, work best in well-insulated and airtight homes. This is because they provide heat at a relatively low temperature, and they can’t keep up with the heat loss of inefficient homes.
The energy efficiency of a hydronic heat pump is expressed as a Coefficient of Performance (COP). Most hydronic heat pumps list a COP of between 3.0 and 3.5, meaning that they supply 3.0 to 3.5 kilowatt-hours (kWh) of heat for each kWh of electricity they consume.
Hydronic heat pumps can’t produce the high temperatures required by most radiators and convectors. Radiant floors, fan coils, and air handlers, on the other hand, are low-temperature heat emitters and are compatible with hydronic heat pumps.
Hydronic heat pumps can also offer the opportunity for cooling if matched to fan coils or to air handlers with ducts. Some innovative buildings use radiant walls or ceilings for cooling. But cold radiant floors have proved troublesome for comfort, especially if you are in your bare feet, and moisture condensation can occur under rugs and carpets.
See The Homeowners Handbook to Energy Efficiency or Residential Energy: Cost Savings and Comfort for Existing BuildingsChapter 6 for more information. For professional information about heating systems and energy efficiency see Saturn Hydronic Systems Field Guide.