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Heat Pump Water Heaters

A quarter of the running cost of a resistance tank, with four conditions attached. All four are real.

By Brijon M., Owner and writer, MadGrey LLC·Last updated October 6, 2026·How we pick →

A heat pump water heater moves heat out of the surrounding air into the water instead of making heat electrically, which is why it reaches a 3.4 to 4.0 UEF against 0.93 for a resistance tank. It needs air volume, a condensate drain, somewhere the compressor noise is tolerable, and a space where cooling the room is acceptable.

This is the biggest single running-cost decision available to an all-electric household, and it is also the most over-promised product in water heating. Both of those are true at once. The efficiency is real and large. The installation conditions are also real, and a heat pump water heater installed in the wrong place quietly runs on its backup resistance element, which means you paid a premium for a resistance tank.

How it actually works

It is a refrigerator run backwards. A compressor and a fan pull heat out of the air around the unit and dump it into the water in the tank. Because it moves heat rather than generating it, it can put more energy into the water than it draws from the wall — that is what a UEF above 1.0 means, and heat pump units are at 3.4 to 4.0.

Two consequences follow directly, and they are the entire practical story of this category. It takes heat out of the room, so the space gets cooler. And it condenses moisture out of that air, so there is water to drain.

The four conditions

  1. Air volume. The unit needs enough air to extract heat from — manufacturers typically specify around 700 cubic feet, or louvered doors with a stated free area. A sealed closet is the classic mistake.
  2. A condensate drain. It produces condensate continuously while running, like an air conditioner. That needs a gravity drain or a condensate pump.
  3. Noise it can make. A compressor and a fan, roughly a dehumidifier's worth. Fine in a garage, fine in an unfinished basement, a problem directly under a bedroom. This is the complaint that repeats most in owner reviews.
  4. A space where cooling is acceptable. In a Houston garage the cooling is a gift. In a heated Minnesota basement your furnace ends up paying for your hot water, which erases the saving you bought.

Where to start

What they cost to run, relative to the alternatives

We will not print a dollar figure, because it depends entirely on your electricity rate and your usage, and a national average would be a number nobody actually pays. What we can give you is the ratio, which is what actually transfers:

Energy per gallon of hot water, relative
ApplianceUEFRelative energy use
Electric resistance tank0.92 to 0.931.0x (the baseline)
A. O. Smith ProLine XE heat pump3.42About 0.27x
A. O. Smith Voltex MAX heat pump3.84About 0.24x
Rheem ProTerra 50 heat pump3.88About 0.24x
A. O. Smith Voltex AL heat pump4.02About 0.23x
Rheem ProTerra 120 V plug-in3.0 to 3.5About 0.27 to 0.31x

Roughly a quarter of the electricity, in other words, for the same hot water. On a household using a lot of hot water that ratio is the most consequential number on this site.

On rebates, and one thing you must not believe

What goes in with it

A water heater is a system, not a box. These are the parts that go in with it, and the ones people discover they need halfway through the job.

  • Drain pan

    A heat pump water heater makes condensate continuously, so this one is not optional.

  • Leak detector

    A condensate line that blocks will overflow long before you notice it.

  • Expansion tank

    Same closed-system rule as any other storage tank.

Who should not buy one

  • Anyone whose only install location is a small sealed closet with no option for louvered doors.
  • Anyone with no route for a condensate drain, unless they are willing to fit and maintain a condensate pump.
  • Anyone putting it directly below a bedroom and sensitive to a dehumidifier-level hum.
  • Anyone in a heated space in a cold climate where the heat it steals is heat their furnace just paid for.
  • Anyone on gas with a working flue, where a gas tank is cheaper to buy, cheaper to run and has a better first-hour rating.

Questions people actually ask

›Are heat pump water heaters worth it?
For an all-electric household with a garage, unfinished basement or utility space, yes — roughly a quarter of the running cost and a better first-hour rating than a resistance tank of the same size. For a sealed closet, no condensate drain, or a spot under a bedroom, no. The full answer.
›How much space does a heat pump water heater need?
Manufacturers typically specify around 700 cubic feet of air, or louvered doors with a stated free area. The unit has to have air to extract heat from; starved of it, it runs on the backup resistance element.
›Do heat pump water heaters work in cold garages?
The good ones do. Rheem publishes a 37 to 145°F ambient operating range for the ProTerra, meeting Northern Climate Specification Tier 4. Below the lower limit the unit falls back to resistance heating, which still gives you hot water but at resistance cost. Cold climates.
›Are heat pump water heaters noisy?
They make about as much noise as a dehumidifier — a compressor and a fan. In a garage or unfinished basement nobody notices. Directly below a bedroom, people do, and it is the complaint that repeats most in owner reviews.
›Does a heat pump water heater need a drain?
Yes. It condenses moisture out of the air it cools, continuously while running, so condensate needs a gravity drain or a condensate pump. This is not optional and it is the second most common install oversight.
›Is there still a tax credit for heat pump water heaters?
Not the federal 25C credit — that expired on December 31, 2025 for equipment placed in service after that date. State HEAR programs and utility rebates do still exist and are often worth more. Rebates.

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