How much does electric underfloor heating cost to run in NZ?

It depends almost entirely on floor area, because the system draws about 150W per square metre. A typical 8 m² bathroom is roughly $53 a month running four hours a day; a 30 m² open-plan living floor is about $199 on the same schedule. Work out your heated area first - it is the number that decides everything else.

Is underfloor heating expensive compared to a heat pump?

Per unit of heat, yes - substantially. Electric underfloor is resistive, so it converts one unit of electricity into one unit of heat, while a heat pump moves two and a half or more. For a whole living area that difference is decisive and a heat pump wins easily. For a bathroom floor it matters less, because the area is small, the runtime is short, and the thing you are buying is a warm floor underfoot rather than a warm room - which no heat pump provides.

Should underfloor heating be left on all the time?

No. That advice circulates because a concrete slab is slow to warm up, so people conclude it is cheaper to hold it at temperature than to reheat it. For a small tiled bathroom that reasoning does not hold - the mass is low, it warms in under an hour, and leaving it on doubles or triples the runtime in the table above. A timer set to the hour before you get up and the hour before bed is almost always cheaper than continuous running.

Does uninsulated flooring waste underfloor heating?

Yes, and it is the single biggest hidden variable. Heat moves in all directions, so a system laid over an uninsulated slab loses a substantial share downward into the ground rather than upward into the room. That heat is still on your bill. If the system is being installed as part of a renovation, insulation under the element is not an optional extra - it is what determines whether you are heating your bathroom or the subsoil beneath it.

Running cost

What electric underfloor heating costs to run in NZ

By Jason Webb· Published 6 August 2026· Updated 6 August 2026· 7 min read

Underfloor heating is priced differently from everything else in a house. There is no wattage on a nameplate to look up, because the system is not an appliance - it is a heating element laid across a floor, and it draws roughly 150 watts for every square metre it covers. Double the floor, double the bill.

So the first question is not "how efficient is it" but "how big is the area". A heated ensuite and a heated open-plan living floor are the same technology with an order of magnitude between their running costs.

Cost by area and runtime

Monthly cost of electric underfloor heating at 36.3c/kWh, by heated area and hours run per day
Heated area	Draw	2 hrs/day	4 hrs/day	8 hrs/day
3 m² - ensuite	450W	$10	$20	$40
5 m² - small bathroom	750W	$17	$33	$66
8 m² - main bathroom	1,200W	$27	$53	$106
15 m² - large bathroom or kitchen	2,250W	$50	$99	$199
30 m² - open-plan living	4,500W	$99	$199	$398

Read across the 30 m² row and the reason underfloor is rarely used as whole-house heating becomes obvious: at 4,500W it is drawing more than two oil column heaters, and it is resistive, so it has none of a heat pump's advantage. Read across the 3-8 m² rows and it looks entirely reasonable - which is exactly where most New Zealand installations sit.

What you are actually buying

It is worth being clear about this, because it changes whether the cost is good value. A heat pump warms the air in a room. Underfloor heating warms the floor, and the room second. In a bathroom that distinction is the entire point: stepping out of a shower onto a warm tile is a comfort no amount of warm air replicates, and no heat pump can deliver it.

Judged as a room heater for a living area, underfloor loses to a heat pump decisively - it costs roughly two and a half times as much for the same warmth, for the reasons set out on our oil column heater page, which applies identically to any resistive element. Judged as a warm floor in a wet room for an hour a day, the numbers in the table above are modest and the comfort is real.

The timer beats the thermostat

The most common expensive mistake with underfloor is leaving it on continuously, usually on the advice that a slow-to-warm slab is cheaper held at temperature than reheated. That reasoning is sound for a thick concrete slab in a passive house. It is wrong for the typical New Zealand case - a thin element under bathroom tiles, which reaches temperature in well under an hour.

Look at the difference between the 2-hour and 8-hour columns above: it is four times the cost for a floor you stand on twice a day. A programmable thermostat set to warm the floor for the hour before the household gets up, and again before bed, captures nearly all the benefit at a quarter of the runtime.

The insulation underneath decides everything

Heat radiates in every direction, including downward. An element laid directly onto an uninsulated concrete slab sends a serious fraction of its output into the ground, where it does nobody any good and still appears on your bill. Rigid insulation beneath the element is what forces the heat upward into the room.

This matters most because it is effectively unfixable later. Once the tiles are down, the decision is made for the life of the floor. If you are specifying a system during a renovation, the insulation layer is not an upsell - it is the difference between the figures in the table above and something considerably worse.

Before you install

Measure the heated area, not the room. Elements are laid only where you walk - not under the vanity, the bath or the toilet - so the billed area is usually smaller than the room. Use that figure in the table.
Insist on insulation under the element. See above. It is the one decision you cannot revisit.
Fit a programmable thermostat, not a switch. A manual switch becomes a system left on, which is the 8-hour column.
Keep it to wet rooms. For living areas, put the money into a heat pump and the insulation around it.

To price your own floor area and schedule, open the calculator - the underfloor row takes square metres directly. For how it ranks against the rest of the house, see the full appliance table.