Sauna not getting hot: causes and what to check

It is usually not a faulty stove but one of the five causes below. Work through them in order, cheapest first. In that order you will usually find the cause within the first two points.

1. The door seal

The most common cause and the cheapest repair. The seal wears out faster than anything else in the sauna, because it goes from outdoor temperature up to 90 °C with every session.

The test takes thirty seconds: with the sauna heated, run your hand around the closed door. If you feel a warm draught anywhere, the seal is not making contact.

A new seal costs little. Check the hinges at the same time: the door should close by itself, without needing to be pushed shut.

2. Ventilation open too wide

While heating up, the outlet should be closed. Wide open, it draws heat out as effectively as an open window in winter.

A very common mistake among people who have heard that “ventilation is important” and leave everything open all the time. Ventilation matters during the session, not while heating up.

3. Damp wood

Wood with more than 25% moisture uses most of its energy evaporating water instead of heating the air. The sauna “heats”, smokes, and the temperature stalls.

A typical sign is dense smoke from the flue and hissing logs. With dry wood there is hardly any smoke.

Wood should season under cover for at least a year, better two. Lay in the winter supply in summer, not in November.

4. Stones packed too tight

Stones stacked too tightly block air circulation through the stove. The stove overheats while the air in the sauna stays cool, so the energy stays in the stones and the stove body.

Solution: take the stones out and restack them more loosely, largest at the bottom. Discard any cracked ones and clear fragments from the stone basket.

5. A stove that is too weak

If the sauna heats up in summer but not in winter, it is not a fault but the wrong stove output for the job. With a lot of glass and frost there is no reserve.

Rule of thumb: about 1 kW per cubic metre of room volume, plus a reserve for windows and hard winters. A more powerful stove costs money, but it is the only lasting fix.

When it really is the stove

Electric stove: if one heating element fails, the sauna heats unevenly and much more slowly. You notice it because one side of the stone basket is clearly cooler. That is a job for a qualified electrician or the stove service.

Wood-fired stove: a cracked body, a burnt-through grate or a leaking firebox door. Then air is drawn in where it should not be, and the firebox does not reach the right temperature.

Before you call the service, go through the five points above. Usually the issue is settled at the first or second one. If you are still stuck, send us a message on WhatsApp with a photo of the setup.