We often get asked if the traditional Finnish sauna is a wet or dry sauna? The answer is it's both! That's why no one can tell you what the correct humidity level should be. Read on to learn the truth about traditional Finnish type saunas and humidity!
While it is true that you use some water in the sauna and it's not a completely dry sauna, you don't need a drain in the floor - while there often is a drain in saunas in Finland, it is mostly there to help with the occasional cleaning, not because it would be needed to use the sauna. Think of your normal floors in your home - while having a drain there would make them easier to clean, you can still mop them without a drain. In Finnish homes, the sauna is usually next to the shower, so installing a drain is just an easy thing to do, not a requirement.
We think that people are asking the question about dry and wet saunas because of the common image of Turkish sauna, or a steam bath. Those are different from a Finnish type sauna because in those the steam is the only source of heat, and you need a lot of it: 100% humidity, in fact. That causes the steam to first condensate on all the surfaces of the sauna, and then drip down on the floor. In Turkish type saunas, a drain is most definitely needed - but you don't need that with a Finnish type sauna!
You can use a traditional sauna without any water, but honestly, dry saunas are a bit boring. Löyly (Finnish word for the steam given off by the heater rocks) gives the sauna real spirit, and it also gives you control over your sauna experience. Not hot enough? Throw some löyly! Overdid it and it got too hot? No worries, it's very temporary. The heat will make the extra steam go away in a minute. If a minute feels too long, you can either "step down" if you have 2-tier benches, or just take a break and go outside.
Doing the löyly is very easy to learn, as you get instant feedback on how strong it is. This also changes a bit with different saunas - smaller saunas have "shorter cycles" so to speak - the steam is very immediate and also tends to disappear sooner. In larger saunas, it may take a few seconds more for the steam to reach your skin, and it doesn't feel quite as "sharp".
This is why we recommend you consider getting a sauna "one notch larger" than you otherwise would - the heat in larger saunas feels more mellow, just the way I like it. Don't overdo it though - getting a 10 person sauna for 1 person use is overkill, as it will just increase the heating costs for very little benefit. On the other end of the spectrum, we only recommend 2 person saunas if there's an acute lack of space, as they can be a bit too small (still better than no sauna!). 4 person saunas are usually our recommended minimum.
In Finnish type saunas, the main source of heat is the heater (as opposed to a steam generator in steam rooms). Without applying water on the rocks, it will only give "dry" heat. Without doing the löyly, the humidity in a Finnish type sauna would be around very dry 5-15%. Add water into those stones, and the humidity rockets closer to 100%, just temporarily. That's why this kind of a sauna is both wet and dry sauna in one!
Depending on your application of löyly, humidity may stay fairly high, or go down towards the low figures. The real enjoyment is not found in keeping a static humidity level - it's in the ebb and flow of increase and decrease. That's why it's impossible to answer what the humidity in a Finnish sauna is - it is exactly what you feel it should be!
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