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Size electric radiant floor heat under tile: heated area (open floor only), watts at 12 or 15 W/sq ft, amps, thermostat and daily running cost.
With these inputs:
| Result | Value |
|---|---|
| Heated mat needed | 45 sq ft |
| Room area | 60 sq ft |
| System wattage | ~540 W |
| Daily energy | 2.2 kWh |
| Est. monthly cost | $11.02 |
Buy the mat size at or just under your heated area — mats cannot be cut, only the mesh can.
<> Heated area = room area minus anything fixed to the floor (vanity, tub, toilet footprint, cabinets, appliances). A typical bathroom loses ~25%, a kitchen with cabinets ~40%. Heat under a cabinet can damage it and wastes energy. Floor-warming systems run ~12 watts per square foot; systems meant as a primary heat source run ~15. Running cost assumes the mat cycles at full power for your daily hours — thermostats with floor sensors typically cut real consumption 20–30% below that.
Less than people fear: a 45 sq ft bathroom mat at 12 W/sq ft draws about 540 W — like a few light bulbs. At 4 hours a day and $0.17/kWh that is roughly $8–11 per month.
Not if installed correctly. Embed the cable fully in thinset or self-leveler, never turn the heat on until the mortar has cured (usually 7–28 days per manufacturer), and ramp the temperature gradually.
Mats are faster and give perfectly even spacing — best for rectangular rooms. Loose cable costs less per square foot and fits irregular shapes better. Both end up the same temperature under tile.
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