Heat pumps, explained
A heat pump is an air conditioner that can run in reverse. In summer it moves heat out of the house; in winter it moves heat in, even from cold outdoor air. That one trick is why it heats a home using far less energy than resistance heating or burning fuel.
What it does, in one paragraph
Refrigerant in the outdoor unit absorbs heat from the air (there is heat in air well below freezing), a compressor concentrates it, and the indoor unit releases it into the house. Because it moves heat instead of making it, a modern unit delivers two to four units of heat for every unit of electricity it uses. The same equipment cools in summer.
The main types
- Ducted (central). Replaces or works alongside a furnace, using the existing ducts. Best when ducts are in good shape.
- Ductless (mini-split). One outdoor unit feeding one or more wall or ceiling heads. Good for homes without ducts, additions, or zoning a few rooms.
- Dual-fuel. A heat pump paired with a gas furnace that takes over on the coldest days. A pragmatic choice in very cold places with cheap gas.
- Heat-pump water heater. The same idea applied to a hot-water tank. Often the single best upgrade for a home with an electric tank.
When it makes sense
- You heat with electric resistance (baseboards, an electric furnace), oil or propane. The savings are usually largest here.
- You need to replace both a furnace and an air conditioner around the same time.
- Your home has no cooling and you want some.
- You have already done the air sealing and insulation, so a right-sized unit can be smaller and cheaper.
When to think twice
- Your electricity rate is very high and your gas rate is very low; run the numbers for your utility.
- The envelope is leaky and uninsulated. Fix that first or the unit will be oversized and expensive.
- The electrical panel is full or small. Ask whether an upgrade is needed and what it costs.
Cold climates
Older heat pumps lost most of their output in freezing weather. Modern cold-climate models are rated to keep heating well below freezing, and many are tested at very low outdoor temperatures. Ask the installer for the unit's rated capacity at your design temperature, not just its summer rating.
Living with one
- Set it and leave it. Large thermostat setbacks can trigger backup heat; small ones or none are better.
- Keep the outdoor unit clear of snow and leaves.
- Expect gentler, longer-running heat than a furnace's blasts. That is normal.
Questions to ask before signing
- Did you do a load calculation for this house, and can I see it?
- What is the unit's heating capacity and efficiency at my winter design temperature?
- Will the existing ducts handle the airflow, and were they tested for leaks?
- Is backup heat included, and when does it switch on?
- Which programs may apply, who applies, and what paperwork do they need before installation? Then check those terms yourself.