In a traditional sauna, the temperature and humidity interact and can be controlled by splashing water on the rocks. This steam, or löylyä is mandatory for a true sauna experience. When you splash water on sauna rocks, water vapor transfers heat energy from the rocks to the surrounding air.
Ideal Temperature For a Sauna – Use the Rule of 200
Due to the effect on relative humidity, you can’t answer what the ideal temperature for a sauna is without addressing humidity. The way TyloHelo, The North American Sauna Society, and others address the ideal temperature including humidity is with the ‘Rule of 200.’
The “Rule of 200” says the sweet spot for most people is when the Temperature and Relative Humidity equals 200 degrees fahrenheit. The theory rests on the idea that a bathers comfort is a function of temperature and humidity.
So if the temperature is 165 F, there could be up to 35% humidity before some sauna users feel uncomfortable. As the temperature rises, the humidity should go down, which will happen naturally.
You may notice that 200 (t+rh) is a natural sweet spot for your sauna. As the temperature rises, you will need to make a lot of steam to keep the relative humidity above 30% (if you have proper ventilation). The amount of water vapor air can hold increases significantly as you approach 200 degrees.
The rule of 200 also implies that saunas will either be hot and dry, or steamy with lower heat. Preferences vary, and both have distinctive benefits (read more about sauna benefits here.)
Hot and Dry Sauna Benefits
Hot and Dry saunas are better for aiding the recovery of a workout by making muscles relax.
Very hot sauna sessions can also help condition the cardiovascular system in a way that mimics actual exercise. If you’ve read about how sauna sessions have the same effects as working out, they are probably talking about hot, dry sauna sessions.
Hot dry sauna sessions are also going to be the best way to get healthy skin benefits of sauna. Simply, hot dry saunas create the perfect environment for sweating.
Sweating improves blood flow to the skin, removes dead skin cells, and can remove toxins.
How hot is too hot? Well, the World Sauna Championships were discontinued after one finalist died and the other was sent to the hospital after spending 6 minutes at 110C (230F). Listen to your body, and know your first few sessions might be short. Sauna is not a competition.
Steamy, Less Hot Sauna Benefits
Sauna is not a competition, and many consider the very hot, dry sauna to be abrasive. They would prefer a gentler heat that they can stay in for longer and really relax.
The löyly at softer temperatures is considered gentler and more therapeutic than in extremely hot saunas, where the water seems to explode as it hits the rocks.
Soft, steamy heat is also best if you’re using skin care products that you want to penetrate deep into your skin. The steam opens pores.
Gentler heat is also excellent for meditation, yoga, and other spiritual practices where heat is not the only focus.
If you have children or folks with medical conditions in the sauna, you will also want to start with a very soft heat.
About Relative Humidity
Relative humidity is a measurement of the ratio of water vapor at a given temperature. The amount of water vapor it can hold increases as temperature rises.
People often confuse relative humidity with absolute humidity in saunas. Since we are measuring relative humidity, the sauna may not feel (or be, in absolute terms) any less humid as temperature rises, even though relative humidity drops.
Getting it Right With Electric Stoves
Both electric and wood burning sauna stoves can be achieve ideal loyly, as long as the stove is powerful enough for the room and it has adequate rocks.
It’s important that the sauna rocks are heated first, and the room is heated by the rocks and steam. If you or the room are being heated directly by the heating coils or fire, it will likely feel harsh or unpleasant.
Wood burning saunas typically heat up faster and provide additional sounds and glows that add to the experience. You can find the best wood burning sauna heaters here.
Infrared saunas are unable to reach 200 as a function of temperature (f) and relative humidity (rh). The maximum temperature range is 105-120 F and they do not offer humidity control.
Is the rule of 200 an exact science? Absolutely not. But it is a good way to think about how heat and humidity interact in the traditional sauna. HELO even includes it in in their sauna heater manuals and guides.
Get on the bench and experiment.