Electric Underfloor Heating Cost: Running Cost and Size Chart (UK)
A 4 × 3 m room with 80% of the floor heated at 150 W/m² needs about 1,440 W of electric underfloor heating, which is 6.3 A at 230 V. At 6 hours a day and 27p per kWh it costs £2.33 a day, or about £70 a month. The underfloor heating calculator does it for your own room, output and tariff.
Size and cost by room
With 80% of the floor heated, 150 W/m², 6 hours a day and 27p per kWh:
| Room | Heated area | Power | Current | Cost per day | Cost per month |
|---|---|---|---|---|---|
| 2 × 2 m | 3.2 m² | 480 W | 2.1 A | £0.78 | £23 |
| 3 × 2 m | 4.8 m² | 720 W | 3.1 A | £1.17 | £35 |
| 3 × 3 m | 7.2 m² | 1,080 W | 4.7 A | £1.75 | £52 |
| 4 × 3 m | 9.6 m² | 1,440 W | 6.3 A | £2.33 | £70 |
| 5 × 4 m | 16.0 m² | 2,400 W | 10.4 A | £3.89 | £117 |
| 6 × 4 m | 19.2 m² | 2,880 W | 12.5 A | £4.67 | £140 |
Monthly cost by price and hours
For the 1,440 W floor of a 4 × 3 m room:
| Price per kWh | 1 hour a day | 3 hours | 6 hours | 10 hours |
|---|---|---|---|---|
| 8p | £3 | £10 | £21 | £35 |
| 15p | £6 | £19 | £39 | £65 |
| 20p | £9 | £26 | £52 | £86 |
| 27p | £12 | £35 | £70 | £117 |
| 35p | £15 | £45 | £91 | £151 |
Which heat output?
| Output | Power for this room | Current | Cost per month |
|---|---|---|---|
| 100 W/m² | 960 W | 4.2 A | £47 |
| 150 W/m² | 1,440 W | 6.3 A | £70 |
| 200 W/m² | 1,920 W | 8.3 A | £93 |
- 100 W/m² is comfort heat on an insulated floor or under wood or laminate.
- 150 W/m² is the usual choice under tiles, to warm the floor in a bathroom or kitchen.
- 200 W/m² suits main heating in a conservatory or a cold, concrete floor, with insulation underneath.
Save money
- Heat only the floor you use. Leave the area under the bath, vanity and units. Heating the whole 12 m² floor would take 1,800 W against 1,440 W.
- Insulate underneath. Insulation boards under the mat send the heat up, and cut the warm-up time and the cost.
- Use a programmable thermostat with a floor probe so that the floor heats only when you are about to use the room.
- Run it for a short time. A floor takes an hour or so to warm up, so start it before you need it, and turn it off when you leave.
Installing it
- Test the mat with a multimeter before, during and after laying it: a damaged heating wire cannot be mended under tile.
- The mat goes on a dedicated circuit with a 30 mA RCD. Most thermostats are rated for 16 A, so very large rooms need a second thermostat.
- Use a flexible tile adhesive that is approved for underfloor heating, and let it cure before turning the heating on.
- A qualified electrician makes the final connection and gives a certificate.
For the cost of other appliances, use the electricity cost calculator, and for tiles see the tile calculator. A heating mat at 1,920 W for this room (200 W/m²) costs £93 a month. These are estimates at the stated prices.
Frequently asked questions
How much does electric underfloor heating cost to run?
A 4 × 3 m room with 80% heated at 150 W/m² uses 1,440 W. For 6 hours a day at 27p per kWh that is £2.33 a day, or about £70 a month.
How many watts per square metre for underfloor heating?
Usually 150 W/m² under tiles, 100 W/m² as comfort heat on an insulated floor, and 200 W/m² if it is the main heat in a cold room.
Is electric underfloor heating expensive to run?
Per hour it costs about the same as a 1.5 kW heater: 39p an hour for this room at 27p. It is cheap to run for a small room for a few hours, and costly if it heats a large floor all day.
Can electric underfloor heating be the main heating?
Only in a well-insulated room at 200 W/m² or more with the whole floor heated. It is usually a comfort heat that warms the floor and takes the chill off.
Do I need a qualified electrician to fit underfloor heating?
The heating mat needs a dedicated circuit and a 30 mA RCD, and the final connection and testing should be done by a qualified electrician, who will provide a certificate.
More guides
Tools & materials for this project
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Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and check the Building Regulations and any planning rules for anything structural or close to a boundary.