Temperature at each height
Hot air rises, so a sauna has layers. The thermostat's sensor sits high on the wall or near the ceiling, where it is hottest. The table is our heat model for a typical indoor room at three settings.
Set to 158 °F
- Ceiling158 °F
- Head, upper bench152 °F
- Feet, upper bench120 °F
- Head, lower bench142 °F
- Floor100 °F
Set to 176 °F
- Ceiling177 °F
- Head, upper bench169 °F
- Feet, upper bench130 °F
- Head, lower bench157 °F
- Floor106 °F
Set to 194 °F
- Ceiling194 °F
- Head, upper bench185 °F
- Feet, upper bench140 °F
- Head, lower bench171 °F
- Floor112 °F
Our heat model at the end of heat-up for a 2.0 × 1.8 × 2.1 m indoor room with a glass door, 68 °F around it. The thermostat reads the ceiling; your head on the upper bench sits a few degrees lower and your feet much lower.
That is why the upper bench should sit about 1.0–1.2 m below the ceiling (bench height), and why a room that is too tall feels cool on the benches even when the thermostat says 80 °C.
Humidity and löyly
A sauna is dry between throws: at 80 °C the relative humidity is only a few percent. Throwing water on the stones (löyly) turns it into steam: one 250 g ladle in a 10 m³ room adds about 25 g of water per cubic metre, which raises the humidity by roughly 8 percentage points at 80 °C and makes the heat feel much stronger for a minute or two. McGill University's Office for Science and Society describes typical Finnish sauna conditions as about 80–90 °C at face level with 10–30% humidity.
Choosing your setting
- Many people bathe at 70–90 °C; start lower, sit on the lower bench and leave when you have had enough.
- With lots of löyly, a lower setting feels just as hot.
- Health first: see sauna safety and ask your doctor if you have a heart condition, are pregnant or take medication.
Thermometer and thermostat
The control unit measures where its sensor is (follow the heater's manual for the sensor position); a separate thermometer at head height on the upper bench shows what you actually feel. Expect it to read lower than the thermostat setting.