What does a hot water heat pump cost to run?

A hot-water heat pump is the upgrade path for the household's biggest single energy user. Instead of using electricity directly to heat water like a standard cylinder, it works like a fridge in reverse, pulling warmth from the air. So it delivers the same hot water using 60-75% less electricity, running at a COP of roughly 3 to 4. Over a year that saves a typical household a few hundred dollars.

The appeal is simple. Hot water is one of the largest loads in the house, so a device that does the same job for a third of the power moves the whole bill, not just a corner of it. Like your cylinder, it usually runs overnight on the night rate, so you are combining a cheaper tariff with a far more efficient way of heating.

It is not free of trade-offs. The unit costs a lot more upfront, and it needs a reasonably ventilated space to draw heat from. Its efficiency also drops in cold weather, just when you want hot water most, so in the deep south it works harder. Check the noise too, as the compressor hums like an outdoor heat pump, which matters if it sits near a bedroom window.

For a high-hot-water household on an expensive rate the payback maths is more compelling, and it is one of the few upgrades that meaningfully moves the whole bill rather than shaving a small appliance.

On price, expect roughly $6,000-$9,000 installed (EECA puts a typical job near $7,000; the appliance alone is about $4,500-$6,500 and the rest is labour), versus $2,000-$4,000 to replace a plain electric cylinder. That extra $3,000-$5,000 buys electricity savings of around $300-$700 a year.

So on the full price the payback runs about 7-12 years, and Consumer NZ puts it 'within 10 years'. The important twist is that this shrinks sharply if you are replacing a dead cylinder anyway, since only the gap between the two options counts, not the whole cost. Timing the switch to when your old cylinder fails is the difference between a slow payback and a genuinely smart one.

The calculator lets you compare this row against a standard cylinder for your household size and rate. Seeing the two annual numbers side by side is the quickest way to judge whether the upfront cost is worth it for the way your home actually uses hot water.