How much does an electric hot water cylinder cost to run in NZ?

About $334 a year for a two-person household and roughly $668 for four, assuming the cylinder is on a controlled overnight circuit at 21.8c/kWh. If your cylinder is billed at the full day rate instead, add roughly two-thirds to those figures - which is why checking your tariff matters more here than almost anywhere else on your bill.

Why is my cylinder cheaper to run than the wattage suggests?

Because most New Zealand cylinders are on ripple control - the lines company switches them on overnight when demand and price are low, and the tank holds that heat through the day. A 3 kW element sounds alarming, but it is only drawing power while reheating, and it does most of that reheating on the cheapest electricity of the day. The element rating tells you almost nothing about the annual cost.

Is it worth wrapping a hot water cylinder?

Almost always, if the tank is older and uninsulated. A wrap plus lagging the first metre of pipe attacks standing loss - the heat the tank leaks into the cupboard around the clock whether or not anyone uses hot water. Combined with dropping the thermostat to 60°C it typically trims 10-15% off this load, for a one-off cost of well under $100. Modern cylinders come with much better factory insulation, so the gain is smaller on a newer tank.

Should I set my hot water thermostat lower than 60°C?

No. 60°C at the cylinder is the floor, not a target to beat. Below that, the tank becomes hospitable to Legionella bacteria. The saving from going lower is small and the risk is not worth it - if you want the taps cooler for safety around children, the right fix is a tempering valve on the outlet, which mixes the water down after it leaves a cylinder still stored hot enough to be safe.

Running cost

What an electric hot water cylinder costs to run in NZ

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

A hot water cylinder is the quietest large load in a New Zealand house. There is no switch, no thermostat on the wall, nothing that makes a noise - just a tank in a cupboard that has been keeping water hot since before you moved in. It is typically 25-30% of an annual power bill, second only to heating, and most people have no idea what it costs them.

For a two-person household the answer is about $334 a year. That is lower than most people guess, and the reason why turns out to be the most useful thing on this page.

Cost scales with people, not with wattage

Nearly every other appliance in a house costs what it costs because of its power rating and how many hours it runs. A cylinder does not work like that. The element might be 3 kW, but it only draws power while reheating the tank, and how often it needs to do that depends almost entirely on how much hot water leaves the building - showers, laundry, dishes. EECA's working figure is about 2.1 kWh per person per day, and that scales close to linearly:

Annual hot water cost by household size, billed overnight at 21.8c/kWh
Household	Electric cylinder	Hot water heat pump	Saved per year
1 person	$167	$56	$111
2 people	$334	$111	$223
3 people	$501	$167	$334
4 people	$668	$223	$446
5 people	$835	$278	$557
6 people	$1,003	$334	$668

That linearity is why a flatting household of five notices hot water on the bill and a retired couple often does not. It is also why the standard advice to "take shorter showers" is better targeted at large households than small ones - there is simply more of it to save.

The overnight discount you may already be getting

Most New Zealand cylinders sit on ripple control. The local lines company broadcasts a signal that switches domestic hot water on overnight, when national demand and wholesale prices are at their lowest, and the tank - which is a large, well-insulated thermos - holds that heat through the following day. In exchange you get a controlled or night rate on that circuit, here 21.8c/kWh against a day rate of 36.3c.

Every figure on this page assumes you have that. If your cylinder is billed at the full day rate - which happens on some plans, and on some newer installs where the controlled circuit was never wired up - your real cost is roughly two-thirds higher than the table above. Before doing anything else with hot water, it is worth finding out which of those two situations you are in. It is the single largest swing available, it costs nothing to check, and it is invisible unless you go looking at your invoice.

Standing loss: the bath nobody takes

The other half of the cost is not water you use at all. A tank held at temperature leaks heat into the cupboard continuously, and the element reheats to replace it. Go away for a long weekend and the cylinder keeps working the whole time, maintaining a tank of hot water for a household that is four hundred kilometres away.

This is the part you can attack without changing anyone's habits:

Fit a cylinder wrap and lag the first metre of outlet pipe. One-off, under $100, and it works every day thereafter. The gain is largest on older tanks; modern cylinders have far better factory insulation and less to reclaim.
Set the thermostat to 60°C - and not lower. Below 60°C the tank becomes a viable environment for Legionella. If you want cooler water at the tap, fit a tempering valve, which mixes it down after it leaves a cylinder that is still stored safely hot.

Together those two changes typically take 10-15% off this load. On the four-person figure of $668 that is roughly $84 a year for an afternoon's work.

When a heat pump actually pays back

A hot water heat pump uses roughly a third of the energy to deliver the same hot water, and the saving column above is real money. But the payback maths is more particular than it is usually presented, because it depends entirely on when you ask the question.

If your cylinder is working fine and you are considering replacing it early, you are spending the full installed price of about $4,500 to buy that saving. For a two-person household that is a payback of around 20 years - longer than the unit's expected life. It does not stack up.

If your cylinder has just died, the question changes completely. You are buying something regardless, and a replacement electric cylinder is about $2,000 of that cost anyway. The real decision is the price difference of roughly $2,500, and against that:

Years to pay back a hot water heat pump, by household size
Household	Saved per year	Replacing a dead cylinder	Replacing a working one
1 person	$111	22 yrs	40 yrs
2 people	$223	11 yrs	20 yrs
3 people	$334	7 yrs	13 yrs
4 people	$446	6 yrs	10 yrs
5 people	$557	4 yrs	8 yrs
6 people	$668	4 yrs	7 yrs

Read down that third column and the rule of thumb writes itself: wait until the cylinder fails, then upgrade - especially in a larger household, where the difference pays for itself several times over across the unit's roughly fifteen-year life. Our longer cylinder versus heat pump comparison works through the rest of the decision, including the cases where a heat pump is the wrong answer.

One caveat on the numbers above: they assume the existing cylinder is already on a night rate, which is the harshest possible test for the upgrade. A household paying the day rate for hot water saves considerably more by switching, and pays back proportionally faster.

The order to do things in

Hot water rewards being tackled in the right sequence, and the cheapest steps come first:

Check the tariff. Free. Potentially the largest single change on this page.
Wrap the tank, lag the pipe, set 60°C. Under $100, 10-15% off, permanent.
Reduce the hot water you use. Shorter showers, cold washes. Scales with household size, so most worthwhile in a full house.
Replace with a heat pump - when the old one dies. Excellent on the price difference, poor on the full price.

To put your own household size and your own rate against these figures rather than the national averages, open the calculator - the hot water row takes a people count directly. If you want to see where hot water sits against everything else in the house, the full appliance table ranks all 45.