Heat pump water heaters (HPWH) work the same way as the heat pumps used to heat houses, but instead of transferring the heat to the air inside a house they move it to the water inside a hot-water cylinder.
The running costs of a HPWH are determined by the efficiency of the unit, often described as the coefficient of performance (COP). If a HPWH has a COP of 3 (this is 300% efficient) then it will cost a third as much as a normal electric cylinder would to heat your water.
For any HPWH you are considering, check that the COP doesn't drop too much as outside temperatures get lower. The performance of some heat pumps drops significantly at temperatures below 7°C.
There are two general styles of heat-pump water heaters:
Integral models have the heat pump and the water tank combined into a single unit. The heat pump sits on the top of the tank and the whole unit is installed outdoors, preferably near the house's bathroom.
Split models use an outdoor heat pump unit, which looks similar to a space-heating heat pump. A small pump then circulates water between the outdoor heat pump unit and the hot-water cylinder. There are limits on the length of the piping from the heat pump to the water cylinder, but the shorter the distance the better.
Split models can use your existing hot-water cylinder, although you might wish to replace it if it's an older model.
The main attractions: one of the cheapest water heating options.
The main drawbacks: high initial cost. Performance can vary significantly between different models. Outdoor unit may have reduced lifespan in corrosion-prone areas.
- In most cases a budget price would be between $5500 - $6200 incl GST
