How much cheaper is a hot water heat pump to run than an electric cylinder?

A hot-water heat pump moves heat rather than making it, so it uses 60-75% less electricity for the same hot water. In practice EECA estimates that saves a typical household around $300-$700 a year versus a standard cylinder. The theoretical best case is higher - a big household modelled at a steady COP of 3 approaches $900 a year - but real installs rarely reach it because winter efficiency is lower and many cylinders already heat overnight.

Do hot water heat pumps work in cold NZ regions?

Yes, but less efficiently. Their COP drops as the air gets colder, so a unit that runs at COP 3.5 in Auckland might sit closer to 2.2-2.5 on a frosty Central Otago morning. Most units have a built-in electric element for the coldest snaps, which pushes running costs up. They still beat a plain cylinder over the year, just by a smaller margin in the south.

How long does it take a hot water heat pump to pay for itself?

Installed, a hot-water heat pump runs about $6,000-$9,000 (EECA puts a typical job near $7,000) versus $2,000-$4,000 for a replacement cylinder. On real-world savings of $300-$700 a year, the extra upfront cost typically pays back within about 10 years, per Consumer NZ - quicker if you are replacing a dead cylinder anyway or run a lot of hot water, slower in a colder region.

Comparison

Hot water heat pump vs electric cylinder: NZ running cost

Published 20 June 2026· Updated 8 July 2026· 6 min read

Hot water is the quiet heavyweight of the NZ power bill. Heating gets the headlines, but water heating runs 25-30% of the average household's electricity use - and unlike a heat pump on the wall, the cylinder in the cupboard does its work invisibly. Most people never think about it until it dies.

When it does die, you face a choice that sets a chunk of your bill for the next 15 years: replace it with another standard electric cylinder, or step up to a hot-water heat pump. The difference in running cost is large enough to be worth understanding before the plumber turns up.

How each one actually works

A standard electric cylinder is resistive: a heating element, typically 3,000 watts, sits in the tank and turns electricity straight into heat. It is 100% efficient in the narrow sense that every watt becomes heat in the water - but that is also its ceiling. One unit of electricity buys you exactly one unit of heat. There is no clever trick.

A hot-water heat pump does the same job the way a fridge works in reverse. A compressor of around 750 watts pulls warmth out of the surrounding air and pumps it into the tank. Because it is moving existing heat rather than creating it, one unit of electricity delivers around three units of heat. That ratio is the coefficient of performance, or COP. A COP of 3 means the unit is, in effect, 300% efficient. This is the same physics that makes a heating heat pump so much cheaper to run than a plug-in bar heater - just applied to your water instead of your air.

The annual cost maths

Let's do real numbers at the median NZ variable rate of 36c/kWh - the marginal rate, since changing your water heater changes only variable spend. A water-heating workload is usually quoted in kilowatt-hours per year because it depends on how much hot water you draw, not on a tidy hours-per-day figure. Two households:

2-person home: roughly 2,000 kWh/year of delivered hot-water heat
4-person home: roughly 3,500 kWh/year of delivered hot-water heat

For the cylinder, delivered heat equals electricity used (efficiency 1.0). For the heat pump, electricity used is the delivered heat divided by the COP - we'll use a realistic year-round average of COP 3.0.

Household	Cylinder kWh	Cylinder $/yr	Heat pump kWh	Heat pump $/yr
2-person	2,000	$726	667	$242
4-person	3,500	$1,271	1,167	$424

The maths behind the 4-person cylinder row: 3,500 kWh × $0.363 = $1,271 a year. The heat pump delivers the same 3,500 kWh of heat but only draws 3,500 ÷ 3.0 = 1,167 kWh, so 1,167 × $0.363 = $424. That's a saving of $847 a year for the bigger household, and around $484 for the two-person one - every year, for the life of the unit.

Treat those as a best case, though. They assume a flat COP of 3 and a cylinder paying the full day rate. EECA's real-world estimate is more conservative - around $300-$700 a year for a typical household - because winter COP dips below 3, the unit's element tops up on the coldest days, and many cylinders already heat overnight on a cheaper night rate. The truth sits between the model and the measurement, and depends on your household.

Upfront cost and payback

None of that is free. A like-for-like replacement cylinder runs about $2,000-$4,000 installed. A hot-water heat pump is $6,000-$9,000 installed - EECA puts a typical job near $7,000, and Consumer NZ reported a real install at $8,505 - partly because the unit costs more and partly because some retrofits need new pipework or a sensible spot to put the noisy bit.

So you are spending roughly $3,000-$5,000 extra upfront to save $300-$700 a year in practice. That is a payback of around seven to twelve years on the full price - Consumer NZ estimates "within 10 years" - after which it is money in your pocket for the rest of the unit's roughly 15-year life. The economics are best of all when your old cylinder has just failed: you were going to spend the cylinder money anyway, so only the $3,000-$5,000 gap is the real "investment", which pays back far sooner.

The cold-weather catch

Here's the catch: a heat pump's efficiency depends on the temperature of the air it is pulling heat from. On a mild Auckland afternoon it might run at COP 3.5+. On a frosty Invercargill or Dunedin morning, that can sag to 2.2-2.5, and most units fall back to a built-in resistive element when it is really cold - at which point, briefly, they are no better than a plain cylinder. That is why we used a conservative year-round COP of 3.0 instead of the glossy brochure figure.

It still wins over a full year everywhere in NZ. But a household in Christchurch or further south should expect a slightly smaller annual saving than a home in Auckland, and should pay attention to where the unit is sited.

Noise, siting and the practical stuff

A hot-water heat pump has a compressor and a fan, so it makes noise - somewhere between a fridge and a quiet outdoor heat pump. That rules out putting it right outside a bedroom window or a neighbour's. It also needs a reasonable volume of air to draw from, so a sealed cupboard is out unless it is a split system. Integrated units (tank and compressor in one) are simplest; split units (compressor outside, tank inside) are quieter indoors but cost more to install.

Who should switch - and who shouldn't

Switch if: your cylinder is on its last legs, you have a sensible outdoor or garage spot for the unit, and you live anywhere from Auckland to Canterbury where winters are moderate.
Probably switch if: you are in the deep south but have a sheltered, slightly warmer install location (a garage, not an exposed south wall).
Hold off if: your current cylinder is only a few years old and working fine - the payback clock only starts when you would otherwise be buying a new cylinder anyway.
Look elsewhere if: you have rooftop solar and a controllable cylinder. Sometimes a plain cylinder soaking up free midday solar beats a heat pump running on grid power - the maths flips.

Work out your own number

Your real figure depends on your region's rate and how much hot water your household actually uses. Plug both into the NZ Power Bill Calculator to see the cylinder-versus-heat-pump gap for your own home, then compare it against the other big-ticket items on your bill.

Related guides

Hot water heat pump cost in NZ - the price to buy and install, and how fast it pays back
The most expensive appliances in NZ homes - where hot water ranks
Average NZ power bill by region (2026) - put the saving in context
Day/night power plans - heating water off-peak is another lever