Heat pump water heaters

Heat pump water heaters use similar technology to heat water as heat pumps do to heat rooms. They only use electrical energy to ‘move' the heat - they don't actually ‘make' heat. This makes heat pump systems much more efficient than traditional electric or gas water heaters.


  • A well designed and installed system uses much less energy than standard electric cylinders.
  • Heat pump water heaters can also work in places that aren't good for solar water heaters - places that get less sun like the south side of hills.
  • They can be put on a controlled electricity supply to get a lower electricity price.
  • Some heat pump water heating systems can also give you ‘central heating'. They do this by pumping warm water from the hot water tank around a system of underfloor heating pipes. Some other systems can be used to heat a hot tub, spa or swimming pool more cheaply than using an electric heater.

Keep in mind

  • The upfront cost of heat pump water heating is relatively expensive.
  • Generally, the warmer the outside air the more efficiently the heat pump water heater runs.
  • If you live in a colder part of the country, ask your manufacturer if their system is designed to work at low temperatures. Ask to see performance results at different temperatures for the model you are thinking of buying. If the heat pump won't operate in colder temperatures, then the system may rely on a standard electric element as backup so you won't get the energy savings you've invested in and it may not be suitable for your location. Systems that frequently use an electric booster or backup element in cold conditions can be more expensive to run.
  • Make sure it’s right for your environment - in geothermal areas or coastal areas, heat pump water heaters need to have suitable protection against corrosion. Ask your supplier about environmental considerations in your area.
  • The system needs to be correctly set up to ensure the water in the tank is regularly heated to 60oC to prevent the growth of legionella bacteria.
  • In a minority of cases you may need a building consent to install a heat pump water heater. Check with your council.
  • Use our water heating tool to compare the upfront and ongoing costs of different water heating options for your situation.

Water heating tool

How they work

  • Heat pump water heaters use a refrigerant to extract energy from the outdoor air to heat water, which is stored in an insulated hot water tank.
  • The actual efficiency that you would get from a heat pump water heater depends on the make of the system, the quality of the installation, the average temperatures where you live and the location of the compressor unit.
  • There are two different types of heat pump water heater:
      • split systems and
      • all-in-one units.
  • Split systems have the compressor unit outside and the hot water tank generally inside although the tank can also be located outside the house separate from the compressor. In some cases you can use your existing hot water tank.
  • All-in-one units have the compressor and tank together and the whole system usually sits outside.