How much does a hot water heat pump cost to run in NZ?

About $223 a year for a household of four, against roughly $668 for a standard electric cylinder doing the same job - both billed overnight at 21.8c/kWh. The saving comes from using about 67% less electricity to move the same heat into the same tank.

Do hot water heat pumps work in cold weather?

Yes, but less efficiently, and that matters more in New Zealand than the marketing suggests. The unit extracts heat from the surrounding air, so as the air gets colder its coefficient of performance falls. In a Southland or Central Otago winter a unit sited outdoors will do noticeably worse than the same unit in Whangarei, and most have a resistive backup element that cuts in when it cannot keep up - at which point you are paying cylinder prices. It still works; it just does not save as much in the months you use most hot water.

Are hot water heat pumps noisy?

They have a compressor and a fan, so yes - roughly comparable to an outdoor air conditioning unit, typically in the 45-55 dB range at a metre. That is unremarkable in a garage or an outdoor corner, and genuinely annoying under a bedroom window or against a neighbour's boundary. Because the unit usually runs overnight on the controlled circuit, the noise happens at the worst possible time. Siting is not a detail on this product.

Can a hot water heat pump replace my cylinder in the same cupboard?

Usually not, and this is what stops most retrofits. The unit needs a substantial volume of air to draw heat from, so an integrated model in a sealed hot water cupboard will chill that space and lose efficiency, while a split model needs an outdoor compressor with a run of refrigerant line back to the tank. Either way there is more to it than swapping a cylinder for a cylinder. Get the siting assessed before you get attached to the running-cost figures.

Buying guide

Hot water heat pump running cost in NZ - and where you can put one

By Jason Webb· Published 6 August 2026· Updated 6 August 2026· 8 min read

A hot water heat pump does to your cylinder what a split system did to your plug-in heater. Instead of using electricity to make heat with an element, it uses a much smaller amount of electricity to move heat out of the surrounding air and into the tank. The water ends up at the same temperature; the meter sees roughly 67% less.

What it costs to run

Like a standard cylinder, cost scales with people rather than with wattage - it is driven by how much hot water leaves the house.

Annual hot water cost by household size, billed overnight at 21.8c/kWh
Household	Hot water heat pump	Electric cylinder	Difference
2 people	$111	$334	$223
3 people	$167	$501	$334
4 people	$223	$668	$446
5 people	$278	$835	$557

Those are the honest figures for a household already on a controlled night circuit, which is the toughest comparison for the heat pump. If your hot water is billed at the full day rate, both columns rise by roughly two-thirds and the gap between them widens proportionally.

The when to buy question - and it is a genuinely finely balanced one - is worked through in detail on our electric cylinder running cost page, which sets the payback out by household size for both scenarios: replacing a cylinder that has failed, and replacing one that still works. The short version is that the first is usually a good decision and the second usually is not.

The constraint nobody mentions until the quote arrives

Running costs are the easy part of this product. What stops most New Zealand retrofits is physical: a hot water heat pump needs air, and a hot water cupboard does not have any.

The unit works by pulling heat out of the air around it and dumping cold air out the other side. Put an integrated model - tank and compressor in one cabinet - inside a sealed internal cupboard and it will chill that cupboard within an hour, then spend the rest of the night trying to extract heat from air it has already cooled. Efficiency collapses, and in winter the backup element takes over, at which point you have bought a very expensive standard cylinder.

That leaves three real options:

Integrated unit, sited in a garage or outdoors. Simplest and cheapest. Needs somewhere with genuine air volume, and somewhere the cold exhaust and the noise do not matter.
Integrated unit indoors with ducting. Ducts bring outside air in and exhaust it out. Works, adds cost and complexity, and the ducts have to go somewhere.
Split system. Compressor outside, tank stays where the cylinder was. The most flexible option and the most expensive, and it needs a refrigerant line run between the two.

Get an installer to look at the site before you get attached to the numbers in the table above. It is a short conversation and it determines whether this is a straightforward job or a much larger one.

Noise, at the worst possible hour

The unit has a compressor and a fan, which puts it in the same acoustic bracket as an outdoor air conditioner - typically 45 to 55 decibels at a metre. In a detached garage that is a non-issue.

The complication is timing. Because it runs on the controlled circuit, it does most of its work overnight - so if the unit sits under a bedroom window, or a metre from the neighbour's, that fan runs at 2am. This is the most common source of regret with these units and it is entirely avoidable at the siting stage. Check the manufacturer's decibel figure, and think about which windows the unit faces.

Cold climates take a bite out of the saving

The unit's efficiency depends on how much heat there is in the air to move, so a Whangarei installation outperforms an Invercargill one on identical hardware. In a hard southern winter, a poorly sited unit will lean on its resistive backup element - and while that element is running, the saving is zero.

This does not make a heat pump the wrong choice in the south, but it does mean the annual saving lands nearer the bottom of the quoted range than the top, and that the siting decisions above matter more the colder your region is. Our regional rate table is a reasonable proxy for how hard your winter works the unit - the southern centres with the highest rates also tend to have the coldest air for it to draw from.

Before you commit

Confirm the siting first. It decides the price and, sometimes, whether the job is possible at all.
Ask which way the cold air exhausts, and make sure it is not into a space you use.
Get the decibel figure and stand where the unit will go, at night, in your head.
Check the backup element behaviour - how cold it has to get before it engages, and whether you can see when it has.
Confirm the controlled circuit carries over. The saving in the table above assumes the night rate; losing it in the changeover would be an expensive oversight.

To model your own household size and rate, open the calculator. For the full buy-or-wait comparison, see hot water heat pump versus electric cylinder and what one costs to buy and install.