Electric underfloor heating is popular in bathrooms, kitchens, and extensions because it needs no boiler, no pipework, and almost no building height. It is also the heating type where running costs vary the most, because electricity usually costs more per kilowatt-hour than gas. Understanding the arithmetic — and controlling it properly — is what separates a comfortable floor from an expensive one.
The cost formula
Running costs come down to four numbers:
- Installed power. Heating mats and cables typically deliver 100–200 W per m²; 150 W/m² is a common specification.
- Heated area. The mat covers the free floor area, not the whole room — usually 70–85% of it.
- Effective running hours. The thermostat does not run continuously once the floor is warm. In a well-controlled system, 3–6 effective hours per day is typical in winter.
- Your electricity price. Including taxes and network charges, most European households currently pay somewhere between €0.15 and €0.40 per kWh.
Cost per day = installed kW × effective hours × price per kWh.
Two worked examples
Small bathroom, 6 m². A 150 W/m² mat over 4 m² of free floor gives 0.6 kW. Running 3 effective hours a day at €0.30/kWh costs about €0.54 per day — roughly €16 per month during the heating season. Because the room is small and the floor has thermal mass, this is one of the better uses of electric underfloor heating.
Kitchen-diner, 12 m². A 150 W/m² mat over 9 m² gives 1.35 kW. At 4 effective hours and €0.30/kWh the cost is around €1.62 per day, or close to €50 per month in winter. Here the numbers start to matter, which is exactly where good control pays for itself.
Why electric underfloor heating costs more than a gas boiler
Electric resistance heating converts almost 100% of the electricity into heat, but a modern gas boiler delivers several kilowatt-hours of heat per kilowatt-hour of gas for a lower unit price. On a pure cost-per-kWh basis, electric underfloor heating is therefore usually the more expensive option for whole-house heating, and the cheaper option for small comfort areas such as bathrooms where the floor is the point.
Two situations change the comparison: homes with solar panels, where daytime self-consumption is effectively free heat, and homes on cheap off-peak tariffs, where the floor can be charged like a storage heater.
What a Tuya thermostat actually changes
- Floor sensor control. Instead of guessing at air temperature, the thermostat measures the slab and stops heating when it reaches the limit. That prevents the classic mistake of a floor that stays warm for hours after the room is already comfortable.
- Accurate schedules. Heat the bathroom in the morning and evening only, not around the clock.
- Weekly patterns. Weekday and weekend routines are different; a schedule respects that without manual adjustment.
- App control. Turn the floor off when you leave for a weekend instead of discovering it on your return.
- Automation. Link the floor to a humidity sensor so it assists drying only when needed.
Realistic savings
A thermostat does not change the physics of the cable, so savings come from shorter running times and fewer wasted hours. Typical improvements over a basic on/off thermostat with no schedule are in the 10–20% range, with the higher figures coming from rooms that were previously heated all day for occasional use. On the kitchen example above, 15% is roughly €90 per heating season; on the bathroom, €25–30.
Cheaper ways to run what you already have
- Use the floor sensor limit correctly. Around 26–28°C is comfortable underfoot for most floor finishes and much cheaper than a 35°C slab.
- Lower the air setpoint. Underfloor heating feels warmer than radiators at the same air temperature, so 20°C is usually enough.
- Shift to cheap hours. If your tariff has a night or valley window, charge the slab during it. Screed releases heat slowly, so this works well.
- Use solar surplus. Programme the floor for the middle of the day when the panels are producing.
- Reduce heat loss. Insulation boards under the mat, draught-proofing, and a well-fitted door make a measurable difference in small rooms.
- Do not heat the whole room to heat the floor. Zone the mat, and heat only the walking area.
Installation notes
- Match the thermostat’s load rating to the mat — a 3,000 W mat needs a thermostat rated above it, typically 16 A.
- The floor probe must be in a conduit so it can be replaced without lifting tiles.
- Electric underfloor heating needs its own earthed circuit and RCD protection; this is not a DIY electrical job in most European countries.
- Keep the mat away from sanitary ware, cupboards, and fixtures that block heat.
To compare models and wiring options, see the complete Tuya WiFi thermostat guide. If you are choosing between a smart and a mechanical thermostat, the numbers are broken down in this comparison, and the schedule templates are in the practical setup guide. Browse the Tuya smart home product collection for thermostats with floor sensors and the matching sensors and plugs.