bathroom ~4-6, kitchen ~10-15
Advanced options
What The Underfloor Heating Cost Calculator Works Out
- Per day: heated area x 150W per m2 x hours on x a 60% duty cycle once the floor is warm, divided by 1,000 for kilowatt-hours and multiplied by your electricity rate (defaults to the current Ofgem price cap unit rate). An 8 m2 bathroom-and-kitchen combination on a four-hour timer draws about 2.9 kWh, 70p to 80p a day at the current cap.
- Per heating season: the daily cost multiplied by 180 days, roughly October to March. The 8 m2 example lands around GBP 140 a season.
- Electric vs wet: electric mats are cheap to install and premium to run; wet systems (boiler or heat pump pipework in screed) cost three to four times more to install and roughly a third to run. Small rooms and short hours suit electric, whole floors and new builds suit wet.
- Mat output (advanced): electric mats are sold at 100W to 200W per m2; 150W is the retrofit standard, 200W for conservatories and cold floors, 100W under some wood finishes.
- Duty cycle and days (advanced): with insulation boards beneath and a floor probe, the mat cycles 50% to 70% of the time once warm; an uninsulated mat heats the subfloor and the room below with equal enthusiasm and runs much harder. Adjust the season length for your climate and habits.
- Per hour (advanced): the connected load of the mats and the average draw, useful for checking the circuit and the thermostat rating.
- Install costs (advanced): electric mat materials and fitting at GBP 50 to GBP 75 per m2 against a wet system at GBP 150 to GBP 250 per m2 for retrofit. Both exclude the floor finish.
- Wet system running cost (advanced): the same kilowatt-hours of heat delivered by gas at the current price cap rate through a 90% efficient boiler. Off a heat pump at a COP of 3 to 4, it would be cheaper still.
- Ten-year total (advanced): install cost plus ten seasons of running for each system, with the season in which wet overtakes electric. Under about 10 m2 electric usually stays ahead; whole-house ambitions flip it.
- Per m2 per season (advanced): the running cost per square metre, scaled to a 5 m2 bathroom and a 15 m2 kitchen. Tile and stone transmit heat generously, engineered wood tolerably, and thick carpet with underlay throttles the whole exercise.