Electric underfloor heating running costs per m²: worked examples

Electric underfloor heating is simple to cost because every watt of cable turns into a watt of heat. There is no boiler efficiency or flow temperature to allow for. You need three numbers: the wattage of the mat or cable, the hours it is switched on, and your unit rate.

This guide gives the per-m² figures, works through four typical rooms, explains why the thermostat makes real bills lower than the headline figure, and shows how off-peak tariffs and insulation change the sums. For a wider look at water and electric systems together, see underfloor heating running costs explained.

How do you work out the running cost of electric underfloor heating?

Multiply the heated area by the output per m² to get the wattage, divide by 1,000 to get kW, then multiply by the hours on and by your unit rate. That gives the cost at full power.

1. Find the wattage. It is printed on the mat label. A 4m² mat at 150W/m² is 600W.
2. Convert to kW. 600W is 0.6kW.
3. Multiply by hours. 0.6kW for one hour uses 0.6kWh.
4. Multiply by your unit rate. 0.6kWh × 26.32p = 15.8p.

The unit rate used here is the Ofgem price cap for 1 October to 31 December 2026: 26.32p per kWh for electricity, the GB average for direct debit. Your own rate depends on your region, tariff and payment method, so check your bill and swap in your own figure.

What does electric underfloor heating cost per m² per hour?

Between about 2.6p and 5.3p per m² for each hour the cable is on at full power, depending on the output.

Mat or cable output	kW per m²	Cost per m² per hour at 26.32p/kWh
100W/m²	0.10kW	2.6p
150W/m²	0.15kW	3.9p
200W/m²	0.20kW	5.3p

These are maximum figures. They assume the cable runs flat out for the whole hour, which it does during warm-up but not once the floor has reached temperature.

What does it cost to run in a bathroom, kitchen or conservatory?

Here are four typical rooms, with the cost per hour at full power and the cost of a month of use. The monthly figure follows the same assumption as a Which? worked example: the equivalent of 3 hours a day at full power for 30 days (90 hours). Treat it as an illustration, not a forecast.

Room	Mat	Load	Per hour at full power	90 hours a month
En-suite, 2m² free floor	100W/m²	200W	5.3p	18kWh, £4.74
Bathroom, 4m² free floor	150W/m²	600W	15.8p	54kWh, £14.21
Kitchen, 10m² free floor	150W/m²	1,500W	39.5p	135kWh, £35.53
Conservatory, 10m² free floor	200W/m²	2,000W	52.6p	180kWh, £47.38

Note that the area is the free floor area the mat covers, not the whole room. You do not heat under baths, shower trays or kitchen units, so a 2.4 × 2m bathroom often takes a mat of only 3 to 4m². Our guide to choosing the right wattage explains which output suits which room.

Standing charges are not included. You pay those whether the heating is on or not.

Why are real running costs lower than the full-power figure?

Because the thermostat switches the mat off once the floor or room reaches its set temperature, then back on as it cools. After warm-up, the floor only uses enough energy to replace the heat the room is losing.

One electric floor heating maker makes the point directly in its design manual: a larger installed power does not change the energy used, because the thermostat controls how long the cable is on. A 200W/m² mat costs more per hour at full power than a 150W/m² mat, but it reaches temperature faster and then spends more of each hour switched off.

What really sets the bill is:

• How long the heating is scheduled to run. A bathroom mat on for two hours each morning uses far less than one left on all day.
• The set temperatures. A higher floor or room set point means more hours on.
• How much heat leaks downward. On a bare concrete slab, part of the heat warms the slab and the ground instead of the room.
• Whether it is the main heat or comfort heat. A mat that just takes the chill off tiles in a room with a radiator runs far less than one heating the room alone.

One manufacturer states that a programmable thermostat with a timer can save up to 30% of the electricity bill compared with a thermostat with no timer. That is the maker's figure, not a guarantee, but it shows why a timer matters more than the mat's output.

Is electric underfloor heating cheaper to run than gas or radiators?

Per unit of heat, no. At the October 2026 price cap, electricity costs 26.32p per kWh and gas 7.97p per kWh, so each kWh of electricity costs about 3.3 times as much as a kWh of gas, before boiler losses are counted.

The Energy Saving Trust describes electric (dry) systems as effective for quickly warming small areas such as a bathroom floor, but says they can be costly to run over longer periods or in larger spaces. It also says wet systems are generally cheaper to run. That matches the numbers above: an en-suite mat costs a few pounds a month, while a large open-plan room heated only by electric cable can cost a lot more.

Compared with an electric panel heater or oil-filled radiator, the cost per kWh is the same, because all direct electric heat turns 1kWh of electricity into 1kWh of heat. One manufacturer says floor heating lets you hold the room 1 to 2°C lower than with radiators for the same comfort, which it puts at 10 to 20% less heat loss. Again, that is a maker's claim, so use it as a guide only. For the full comparison, see water vs electric underfloor heating.

Does Economy 7 make electric underfloor heating cheaper?

Only if most of the heating runs in the off-peak window. Economy 7 gives seven hours of cheaper electricity, typically overnight from around midnight to 7am, though times vary by supplier and region. Daytime units are usually dearer than on a standard tariff.

A September 2026 comparison of named Economy 7 tariffs listed off-peak rates of about 12.5p to 14p per kWh and peak rates of about 28p to 30p per kWh. So a bathroom mat that runs mostly in the evening would cost more on Economy 7, not less.

A thin mat in tile adhesive holds very little heat, so it cannot store night-time energy for the day. To use off-peak power for daytime heat you need cable in a thick screed, laid as a storage floor. One manufacturer's design manual describes storage floors with 7 to 15cm of concrete over the cables, charged during a low-tariff window such as eight hours overnight.

How can you cut the running cost?

Insulate under the mat, use a programmable thermostat with a floor sensor, and only heat the hours and areas you need.

• Insulate below the heating. One manufacturer recommends insulation under the system to reduce downward heat loss and warm-up time. On concrete, a cement-coated XPS tile backer board goes under the mat and is ready to tile.
• Use a programmable thermostat. The Heatmiser neoStat-e has 5/2 day, 7 day and 24 hour programming, optimum start and a floor sensor, and switches up to 16A.
• Set sensible limits. A floor limit protects the finish and stops the floor running hotter than it needs to. See floor probes and air sensing.
• Match the output to the room. Use the lower-output mat in small, well-insulated rooms. It will not save energy on its own, but it avoids oversizing the circuit.
• Use your own solar power. If you have panels, run the floor when they are generating. See electric underfloor heating with solar panels.

Frequently asked questions

How much does electric underfloor heating cost per hour?

Multiply the mat wattage in kW by your unit rate. At 26.32p per kWh, a 600W bathroom mat costs about 15.8p per hour at full power and a 1,500W kitchen mat about 39.5p. Once warm, the thermostat cycles it, so the real cost per hour is lower.

Does a 200W/m² mat cost more to run than a 150W/m² mat?

It costs more per hour while it is on, but it heats up faster and then switches off for longer. One manufacturer says installed power does not affect energy use, because the thermostat controls the on-time. Heat loss and hours of use matter more.

How much does it cost to heat a bathroom floor for a month?

A 4m² mat at 150W/m² (600W) running the equivalent of 3 full-power hours a day for 30 days uses 54kWh, which is about £14.21 at the October 2026 price cap. Use your own hours and unit rate for a better estimate.

Is it cheaper to leave electric underfloor heating on all the time?

For a thin mat in tile adhesive, usually not. It warms up quickly, so a timed schedule with optimum start uses less than heating an empty room all day. A thick storage screed is different, because it is designed to charge overnight.

Do insulation boards reduce running costs?

Yes. On a concrete floor, heat goes down into the slab as well as up into the room. An insulation board under the mat sends more of the heat upward and shortens warm-up, which one manufacturer says reduces both downward heat loss and warm-up time.

Can I run electric underfloor heating on Economy 7?

You can, but a thin mat only benefits if it runs in the off-peak hours, typically around midnight to 7am. Daytime units on Economy 7 are often dearer than a standard tariff, so check when the heating will actually run.

Is electric underfloor heating expensive for a whole house?

It can be. The Energy Saving Trust says electric systems can be costly to run over longer periods or larger spaces, and that wet systems are generally cheaper to run. For large areas, compare a water system with a heat pump or boiler.

Sources: Ofgem: energy price cap unit rates and standing charges, Energy Saving Trust: underfloor heating, Which?: underfloor heating costs, Smart Energy GB: what is Economy 7