Why We Use 130 W/m² Heating Film, Not 220 W/m²
Carbon underfloor heating film is sold in different power ratings, from about 80 W/m² up to 220 W/m². More watts can sound better, but under a floor it usually isn't. We sell 130 W/m² film (with 110 and 80 W/m² for well-insulated rooms) and we don't sell 220 W/m² film. Here is why.
In this short video we explain the difference.
A warm floor needs very little power
Underfloor heating works by turning the whole floor into a large, gentle heater. Because the heated area is so big, the floor only needs to be a few degrees warmer than the room. Most wood and laminate floor makers ask for a floor surface of no more than about 27 °C. In a normally insulated room, 130 W/m² is plenty to reach that.
Why 220 W/m² film causes problems
- It runs much hotter. High-output film is typically specified to reach about 55 °C. That is double what a wooden floor should see. The thermostat's floor sensor has to keep switching it off to protect the floor, so the extra power cannot be used anyway.
- Hot spots under furniture. Where a sofa, bed, rug or box covers the floor, the heat cannot escape. The floor sensor is usually somewhere else in the room, so it doesn't notice, and the film keeps running. With high-output film that covered patch gets very hot and can burn the floor. With 130 W/m² film the heat builds up far more slowly.
- It loads the electrics. 220 W/m² draws about 1 amp for every square metre. A 20 m² room comes to about 4.4 kW, around 19 amps, which is more than a typical 16 amp thermostat can switch and may need its own heavier circuit. The same room with 130 W/m² film draws about 2.6 kW, around 11 amps.
- It doesn't heat the room any cheaper. The room needs the same amount of heat whatever film is fitted. Higher-wattage film just delivers it in shorter, hotter bursts.
We learned this the hard way
When we started, we used high-output film too. On real jobs it caused problems, including floors that were burnt where heat built up, so we changed to 130 W/m² and have used it ever since. It warms the floor evenly, stays within floor makers' temperature limits and keeps the electrical load sensible.
Quick comparison
| 130 W/m² film | 220 W/m² film | |
|---|---|---|
| Typical maximum film temperature | Low, gentle heat | About 55 °C |
| Current per m² | About 0.57 A | About 1 A |
| 20 m² room, total load | 2.6 kW (about 11 A) | 4.4 kW (about 19 A) |
| Suits laminate and engineered wood | Yes | Needs careful control to protect the floor |
Which film should you choose?
- 130 W/m²: the right choice for most rooms as main heating.
- 110 W/m² or 80 W/m²: for very well insulated rooms or new builds.
Every Kit PRO uses 130 W/m² or 110 W/m² film. See our heating film, read the underfloor heating film guide, or send us your room size and we will tell you which film and thermostat you need, usually within one working day.