Heat pump water heating

Heat pumps use the same technology to heat water as is used to heat rooms. Heat pump systems 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 less energy than standard electric cylinders.

  • Heat pump water heaters can work in places that aren't good for solar water heaters - places that get less sun like the south side of hills.

  • If cheaper night rate electricity is available in your area, some heat pump water heater models can take advantage of it. Check with your electricity supplier and, if it's available, get your cylinder sized so you can use it. Watch out for the overnight temperatures - if the temperatures are too low the heat pump water heater won’t perform very well.

  • 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

  • Generally, the hotter the outside air the better the heat pump runs. Heat pump water heaters tend to work best in areas with average air temperatures above about 7° Celsius. But most will still run more efficiently than a traditional electric or gas water heater in below-zero temperatures.

  • 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 the standard electric element so you won't get the energy savings you've invested in and it may not be suitable for your location. Systems that use an electric booster or backup element in cold conditions can be more expensive to run.

  • The upfront cost of heat pump water heating is relatively expensive.

  • 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 energy from the outdoor air or ground 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.