The short version
- A heat pump water heater moves heat from the surrounding air into the water, using about a third to a quarter of the electricity of a standard electric tank.
- Location matters: it needs air space around it, a drain for condensation, and it blows out cool, dry air.
- Replacing an electric tank saves the most. Replacing gas saves less, and depends on your rates.
- Plan ahead. Most water heaters are replaced in an emergency, when it's too late to choose.
How it works
A standard electric water heater heats water with a large element, like a toaster. A heat pump water heater has a small heat pump on top that pulls warmth from the air around it and moves it into the water. It's the same idea as a refrigerator, in reverse.
Because it moves heat instead of creating it, a heat pump water heater typically uses about a third to a quarter of the electricity of a standard electric tank. Most also have a backup element for times of very high demand.
UEF: the efficiency rating
Water heaters are rated by UEF (Uniform Energy Factor). Higher is better. A typical gas tank is around 0.6, a condensing tankless gas heater around 0.95, and a standard electric tank a little over 0.9. Heat pump water heaters are rated roughly 3 to 4, which is why their energy use is so much lower.
120V or 240V?
120V plug-in models
Plug into a standard outlet, which can avoid panel work and new wiring. They heat more slowly, so a larger tank is usually recommended.
240V models
Need a dedicated 240V circuit, like an electric dryer. They recover faster after heavy use and are rated slightly more efficient.
If your panel is tight, a 120V model can be the difference between a simple swap and an electrical upgrade. The Panel Readiness Check shows how each option affects your panel.
Where it can go
Heat pump water heaters need air around them to pull heat from. Manufacturers typically call for a fairly large space or a vented door, so check the installation manual for the model you're considering. A garage, basement or roomy utility area usually works well. A small closed closet usually doesn't without venting.
They also make condensation, so they need a drain nearby, and they blow out cool, dry air. In a garage that's rarely an issue, and in summer it can even be a bonus. They make about as much noise as a refrigerator or dehumidifier.
Will it save you money?
Replacing an electric tank almost always saves a lot. Replacing a propane tank usually does too. Replacing a gas tank saves less, and replacing a newer condensing gas tankless heater may not save anything on running cost alone. The Heat Pump Water Heater calculator compares all of these for your household and rates.
Hot water use matters too: bigger households and long showers mean more savings. And pairing a heat pump water heater with solar lets it run on your own daytime power.
Plan the switch before you need it
Most water heaters last roughly 10 to 15 years, and most are replaced the day they fail. In an emergency, people usually get whatever can be installed that afternoon, which is typically another gas tank.
If your water heater is getting older, find out now what a heat pump model would need in your home: space, a drain, and power. Then you can switch when the time comes instead of scrambling.
Questions to ask your contractor
- What size tank do you recommend for my household, and why?Heat pump models often benefit from a slightly larger tank.
- Is there enough air space where it will go, or do we need venting?
- Where will the condensate drain go?
- Do you recommend a 120V or 240V model for my panel?Ask whether the 240V option would require a panel upgrade.
- How should the operating mode be set?Most units have efficiency, hybrid and electric-only modes.
- What rebates are available, and will you handle the paperwork?Local programs change; ask what applies today.
- What's the warranty on the tank and the heat pump?
Common mistakes to avoid
- Waiting until the old tank fails. Emergency replacements rarely leave time to switch.
- Squeezing it into a small closet. Without enough air, efficiency drops.
- Forgetting the drain. Condensation has to go somewhere.
- Choosing too small a tank. Slower recovery means a bit more capacity helps.
- Leaving it on electric-only mode. That gives up most of the savings.
Run the numbers for your home
This guide is general education, not advice for your specific home. Equipment, rebates and PG&E rates change; confirm details with a qualified professional. Unfamiliar term? See the glossary. Have a question it didn't answer? Ask Robert.