“If a carbon film heater runs continuously, will it be damaged – and what happens to the bill?” This question comes up often. Two situations need to be distinguished: a thermostat-controlled system being switched on all day is not the same as the film running at full power non-stop, or without a thermostat.
“Always On” with a Thermostat
When a thermostat-controlled system is left on all day, the film does not run continuously. When the room reaches the set temperature, the thermostat switches the film off, and switches it back on as the temperature drops. The film draws power for only part of each hour. This type of use is:
- safe (with a floor sensor, the limit is never exceeded);
- comfortable (no temperature swings);
- not harmful to the film’s lifespan.
If the Film Never Stops
If the thermostat stays permanently in “heat” mode and the film never switches off, one of the following is likely:
- Insufficient power: Installed power does not cover the room’s heat loss. The sizing calculation should be redone.
- Poor insulation: An open window, uninsulated walls or missing underlay insulation.
- Thermostat set too high: A set point that can never be reached.
- Sensor problem: A badly positioned or faulty sensor.
- No thermostat: The film is plugged directly into a socket.
Consequences of Running Continuously Without a Thermostat
- High bills: The film runs at full power, so consumption is far higher than with thermostat control.
- Overheating: Especially in covered areas, the surface temperature can exceed safe limits.
- Damage to floor coverings: Risk of deformation in parquet and laminate and discolouration in carpets.
- Shorter lifespan: The film and connections age faster at constantly high temperatures. Details: carbon film heater lifespan.
Advice for Correct Use
- Always use a thermostat – preferably one with a floor sensor.
- Set 20–22 °C during the day and 17–18 °C at night.
- If you will be away for a long time, keep the system at a low temperature rather than switching it off.
- Automate your hours of use with a programmable thermostat.
- Do not cover the film with thick cushions or closed-base furniture.
For the benefits of a thermostat, see thermostat-controlled under-carpet heaters.
Frequently Asked Questions
Can a carbon film heater be left on overnight?
Yes, in a correctly installed system with a thermostat; programming a lower night-time temperature is recommended.
Is it cheaper to leave it on or switch it on and off?
Switching off for short periods usually brings no benefit; lowering the temperature when the space is empty is the most balanced approach. See our electricity consumption guide to calculate.
Conclusion
There is no problem with a thermostat-controlled carbon film heater being switched on all day. The problem is a film running non-stop because there is no thermostat or the power is insufficient. If your system runs constantly, contact us for an inspection.
