Applies only to heaters with a mechanical timer switch.
Why does the electric heater don't work in cold conditions?
Heaters equipped with a mechanical timer switch and thermostat do not work in cold conditions, as the heater's built-in overheat protector switch may trip when the ambient temperature drops below -5°C.
For this reason, it is not recommended to install a sauna heater in, for example, an outdoor sauna that does not have basic heating and where the ambient temperature drops below 0°C during the winter season.
If the overheat protector switch trips in cold conditions, the heater can be restored to working order using the reset button on the thermostat. However, this requires the ambient temperature to be at least +18°C.
See instructions for resetting the thermostat here
Why does the overheat protector trip in cold conditions?
The overheat protector tripping in cold conditions is due to the thermostat design, which is related to a change in the IEC 60335-1 standard: If the capillary sensor in the capillary thermostat is damaged, the thermostat must immediately cut off the power supply. An undesirable feature of this function is that the overheat protector is particularly sensitive to cold conditions and usually trips when the temperature drops below -5°C.
Change in the IEC 60335-1 standard for household electrical appliances
The standard change applies to all household electrical appliances with capillary overheat protection. This includes, for example, manually controlled electric sauna heaters, hot water boilers, low-cost electric ovens, drying cabinets, etc.
What kind of electric heater is suitable for a sauna where the internal temperature may drop below 0°C in winter?
An electronically controlled wall-mounted heater with a smaller stone compartment, such as Harvia Spirit or Harvia Moderna, is best suited for a sauna without basic heating.
Electronically controlled heaters are also equipped with overheat protector integrated into the temperature sensor, but due to the control method, this is not as sensitive to cold conditions. The overheat protector is activated with an automatic delay after the heater is turned on, by which time the temperature in the sauna room has already risen (at the height of the temperature sensor) to a sufficiently high level, i.e., at least above 0°C.
Note: We do not recommend pillar-type electric heaters with a large amount of stones for saunas without basic heating. Heaters with a small amount of stones raise the room temperature faster than large pillar-type models.