What Temperature Should a Sauna Be? (UK 2026)

A traditional Finnish sauna (a high-heat, low-humidity sauna heated by hot stones) should run between 70 and 100°C measured at head height on the upper bench. The widely used comfortable range is 80 to 90°C, which is hot enough to bring on a strong sweat without being overwhelming for a normal session. Public and commercial saunas in the UK are typically set around 85 to 90°C.

The heat is dry by default, with relative humidity often in the 10 to 20 per cent range. Pouring water over the stones produces löyly (the burst of steam that briefly raises the humidity and the perceived heat), which is why a Finnish sauna can feel much hotter for a few minutes after a ladle of water even though the air temperature barely changes.

An infrared sauna (a cabin that uses infrared heaters to warm the body directly rather than heating the air) should run much cooler, typically 45 to 60°C. Because the infrared energy heats your skin and tissue rather than the surrounding air, you sweat at a far lower air temperature than a Finnish sauna requires.

This lower temperature is the main appeal of infrared for people who find 90°C uncomfortable, and it is why infrared cabins are popular as home saunas. Do not judge an infrared sauna by Finnish-sauna numbers: 55°C in an infrared cabin can produce as heavy a sweat as 85°C in a traditional one. Most infrared units take 10 to 15 minutes to reach temperature, against 30 to 45 minutes for a traditional heater.

Three things make the felt heat diverge from the wall thermometer, and understanding them is the key to controlling your session.

Beginners should start at the lower end of each range: around 70 to 80°C for a Finnish sauna, or 45 to 50°C for infrared. Sit on a lower bench for the first few sessions and keep them short, building from 5 to 10 minutes up to 15 to 20 as your tolerance grows. There is no benefit to enduring a temperature you find unpleasant - the physiological response to heat is similar across the comfortable range, so the right temperature is the hottest one you can relax in, not the hottest the heater will reach.

Yes. Above roughly 100°C a Finnish sauna becomes uncomfortable and the margin for safe time drops sharply, and very high heat combined with a long session raises the risk of dizziness, dehydration and fainting. The NHS advises staying hydrated and not overdoing heat exposure, and standard sauna guidance is to limit sessions to about 15 to 20 minutes, cool down between rounds, and never use a sauna after drinking alcohol.

Some groups should be more cautious regardless of the temperature, including pregnant women, people with heart conditions or low blood pressure, and anyone feeling unwell. If you feel light-headed, leave and cool down rather than pushing through - that sensation is the body's signal that core temperature is climbing too fast. For a fuller breakdown, see our guide on who should not use a sauna.

Home saunas control temperature through the heater's thermostat, but the heater must be correctly sized for the room first. An undersized heater will never reach 90°C in a large cabin, while an oversized one cycles on and off and heats unevenly. The standard rule of thumb is roughly 1 kW of heater output per cubic metre of cabin volume, adjusted up for glass doors, exterior walls or large windows that lose heat.

Once sized correctly, set the thermostat to your preferred range, allow 30 to 45 minutes to preheat a traditional sauna (or 10 to 15 for infrared), and use the bench height and löyly to fine-tune the felt heat during the session. See our sauna heater sizing guide for the full calculation.