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Howto: Build a sauna

A few times people have asked me hints and tips on how to build a small sauna. I'm not an expert in the field; I was involved in a small group building a smoke sauna, and I've built a small sauna all by myself. And I've experimented with simple sauna-in-a-tent style make-shift constructions. So, I'm not here to share any kind of ultimate wisdom. But I highly encourage Do-It-Yourself mentality, to experiment and to learn by doing. Just remember that with saunas we are dealing with fire and high temperatures, so safety is a real issue to consider; don't risk getting yourself or your buildings burned down because of accidental fire! I repeat: do not neglect safety - think in advance - imagine all the possible ways your construction could cause injury or accidents, and seek to minimize the risk. Always! Also, despite this blog being labelled as "howto" this is not intended as a classical "follow these steps" guide, but more like "consider these points when drafting your own experimental plans." All this being said, let's have a look the points that came to my mind;

Sauna stove

The heart of the sauna is the stove. A primitive sauna stove can be made by heating up a heap of stones with a camp-fire; basically that gives you a version of a smoke sauna. You need to burn fire for several hours to make the stones almost red-glowing hot. Then let the fire go out, make sure all the smoke is ventilated away, and only then you can go to enjoy a sauna bath. This can be used for make-shift sauna experiments, and for ritual purposes etc. But for regular use most of the people prefer such construction which is faster to heat up, and where you can have a sauna bath while the fire goes on. A factory-made Finnish sauna stove is so designed that the flue doesn't go directly from the fire box into the chimney, but the flue makes a horizontal loop or two before going into the vertical chimney. The idea is that as fire and hot air travel in the flue the surrounding sauna stove stones get heated up. And the shape of the flue is so designed that there is maximum surface area of the flue in direct contact with the stones. If you don't have an access to a factory-made stove, I think you could try to hack a DIY-version using almost any kind of ordinary stove. Just install some kind of frame around and above the stove, to keep stones in, having the stones packed on top of the stove, next to the flue / chimney, and probably also against the rear wall of the stove. (Maybe use multiple layers of chicken wire or something? Just make your frame solid enough so that the heap of hot stones wont' collapse.) Take a look at the picture below - it shows over-simplified diagrams of a factory-made sauna stove and an idea for DIY-hack-stove. In reality the factory made stove has the flue making curves more in horizontal plane but I couldn't figure out a way to draw it so, but I think you'll get the idea.

The purpose of the stones is essential. They act as a heat reserve and a buffer. For the sauna bath works best when you cast water onto the stove - and any hot material wears down quickly when exposed to water. The water temperature is substantially lower that the temperature of the stones, and the sudden change in temperature makes any material to crack, sooner or later. But you don't want the metal structure of your sauna stove to crack into pieces after a few times of use. That is why you have stones packed on top of the metal parts. When the stones wear down you can just replace them with solid fresh ones. Also, a heap of stones gets heated up slower than just the ordinary metal lid of a cooking stove. That is good, for it makes the sauna bath experience more smooth and even - instead of the sauna temperature fluctuating quickly up and down you can get maintain an enjoyable temperature. (Which, if you ask me, is anything between 60°C - 120°C, depending on which kind of a sauna bath you'd like to have. Lower temperatures for prolonged relaxation, higher temperatures combined with rolling in the snow or ice-swimming is guaranteed to boost your endorphine levels.) I don't know but I've heard that it is remotely possible that some minerals might release non-healthy gases when heated up - so pay attention to where and what kind of stones you use. Other than that you can use almost any kind of stones - about the size of your fist. Granite turns to sand after a few cycles of being heated up and having cold water thrown on. So maybe look for stones with a solid dense structure, for some reason the best ones seem to be dark in colour, at least considering the mineral we find here in Finland.

Remember the safety! If you are not planning a temporary make-shift sauna but a more permanent structure, make sure to install fire-proof materials under the stove, on the walls near the stove, and on the ceiling above the stove. And extra lot of fire-proof insulation around the place where the chimney goes through the ceiling. But I hope these principles are familiar for any DIY-builder who has basic experience with ordinary stoves. Just remember that the sauna stove is often heated up to higher temperatures, and might stay hot for hours, so consider using double the insulation you'd otherwise do.

Dimensions and air circulation

Basically, almost any kind of a room can be used as a sauna. Finnish Defence Forces have sauna tents. So, all you need is a stove and enough of a walls and ceiling to keep the hot air in for a while. Make sure that the space is high enough - for the pleasantly warm and the best feeling of the löyly will be above the level of the stove stones. Ideally, you'd construct sauna benches so that when you sit on the top bench, you'll toes will be at the same level where the topmost stove stones are. Otherwise, in an unlucky situation, your toes might feel cold while your head is unbearably hot. So design the dimensions so that your toes will be comfortably warm!

You'll need fresh air. The fire burning in the stove consumes oxygen, so without a proper intake of fresh air the sauna experience might quickly get exhausting if there is not enough oxygen in the air. Ideally, the fresh air should come in near the floor level, next to the stove. That way the colder outdoor air gets warmed up as soon as it gets into the sauna room. The minimum is to place an outgoing ventilation shaft near where your head is when you sit on the sauna bench. It is good if this outgoing ventilation has some sort of lid or something which can be used to control the draft. Also, you can have a second ventilation hole near the floor level under the benches.

I think you don't need to treat the wooden parts. The walls and the benches can be made of plain simple sawn timber, maybe just planed so that they feel nice to bare skin. After each sauna bath add some firewood into the stone, and open all the air ventilation for maximum air circulation. Some people leave the sauna window open when they are finished with the bath. The idea is to make the empty sauna room warm enough so that it will quickly get dry, letting all the moisture out. That way the timber doesn't start to rot. Also, if there are periods when you don't regularly take a sauna bath consider warming up the sauna room just for the sake of the sauna itself - you don't want the sauna room to rot, nor to grow mould, so keep the room extra dry all year round.

The löyly and the vihta

There are different kinds of sauna traditions and habits around the world. In the Finnish version löyly is considered essential to the sauna experience - although, it is also perfectly fine and recommendable to enjoy prolonged time in milder temperature with no löyly, but usually people do that as the final phase of a sauna bath, when they first have enjoyed proper löyly. I really don't know if there is an English word for löyly, but on the physical level it is the steam you get when you pour water on the hot stones. At first it might feel uneasy, so start with milder temperature and only a little bit of water. Your body will quickly adapt to it - I have seen people with zero sauna experience becoming sauna enthusiasts after having a sauna bath two or three times. The warm moisture in the air makes you sweat, and it feels like a remedy for many kind of physical and emotional pains. Needless to say, in the old Finnish folk culture löyly is considered to have magical properties, it was often imagined as a physical manifestation of an unseen spirit. A fresh clean plain water is good. But sometimes you can mix a little bit of beer with the water. Or essential oils, or any other kind of liquid which will give extra scent - I know there are purists who despise this kind of advice, so try this only if you find the scents enjoyable, and don't force other people to inhale your favourite scents if they feel differently. Sauna is supposed to be a place where everyone is equal in their birthday suit, so keep the experience so that it respects everyone in the sauna room.

In Finland the typical vihta is a bunch of birch branches with fully grown leaves. You soak the vihta in warm water and then beat yourself with it. The effect is a lot like massage. Also, minerals and essential oils surely play their role in the healing effect of the vihta. If you are into herblore, feel free to experiment with vihta made of various kind of trees or plants. Even the surprising variants work well, especially if soaked in boiling-hot water and then let to slowly cool down to a bearable temperature. Juniper is said to have essential oils which have anti-headache effects. Nettles have been used as the general cure to boost your immune system. Nettles won't sting after they are soaked in hot water so no, it is not a form of torture, but just a traditional way of herbal healing. I don't know for sure, but I'm under the impression that this aspect of the Finnish sauna tradition is diminishing, for we have more and more urban saunas which often aren't best suited for using a vihta. No matter how you use it, vihta will spread around leaves and other organic material, so afterwards you have to pay extra attention to cleaning up the sauna room.

Feedback and questions

This is what came to my mind today. If I forgot to mention something, just post a comment and I'll reply. Also, I must admit that personally I have never tested the DIY-hack-version of a sauna stove, for factory made models are easily available here in Finland. So it would be super interesting to hear a word of two if anyone ever gets to implement the idea. And, naturally, it would be even more interesting if someone has tried and tested another kind of versions of a DIY sauna stove. I would be glad to add pictures and ideas posted by fellow experimental DIY-sauna builders out there, so feel free to post your stories =)

Left: a factory made stove. Right: a DIY hack to turn an ordinary stove to a sauna stove
An over-simplified diagram of a sauna stove
A diagrman of a sauna room
A diagrman of a sauna room
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Comments

Thank you.

Hello Erkka! Thank you for the wonderful blog posts, pictures, and all of your creative endeavors. You are making me want to take a trip to Finland when this virus settles down! As I was looking at the DIY sauna stove drawing I had a thought...have you ever heard of Rocket Mass Heaters? They're wonderfully fuel efficient as well as very easy to build, they operate similar to the first drawing however the flue is longer and the firebox is smaller. They take advantage of a large thermal mass being heated by the super hot gases and smoke flowing through the flue. I'm thinking it would be very easy to create a variant of one specifically for sauna use, as in using sauna stones as the thermal mass the heater needs to operate effectively. Here's a link to a great homesteading and permaculture forum where I learned about these heaters: https://permies.com/f/260/rocket-mass-heaters

Thanks again for everything, I've only recently discovered UnReal World and I have to say it's one of the best games I've played in a long time!

PS If you are interested I can send you a PDF that explains how Rocket Mass Heaters work in greater detail and includes plans on how to build one yourself

Hello, welcome aboard and thanks for your feedback!

Yes, I've heard of Rocket Stoves and Mas Heaters. I've been experimenting with different kinds of make-shift Rocket Stove constructions for my summer kitchen, but I've always taken them down for the winter. I'm hoping that this summer I get to build a more permanent outdoor kitchen, based on my previous experiments. And, some year in the future I'd like to build a small greenhouse with a Rocket Mass Heater - but that is not an immediate plan at the moment, so at this point I'm not asking you to send that interesting PDF. For I already feel more or less over-burdened by the constant overflow of digital information, so I try to keep my daily life simple with only limited amount of information to process each day =)

Rocket Mass Heaters have some interesting features for small-scale DIY-builders. And the basic principle is pretty familiar for anyone who has grown up here in the north. For different versions of Mass Heaters have been used in Finland since the ancient times - you just need one to keep your house heated during the winter. With a quick search I couldn't find a diagram of the typical Finnish mass heater, but here is a wikipedia article of the model which was the most commonly used type in Finland for most of the 20th century, until those were gradually replaced by central heating systems or electric radiators. Although the wikipedia article doesn't contain a structural diagram, I'd guess by just looking at the picture one can imagine how the flues run up and down inside the tall structure. That design is said to capture about 80% of thermal energy of the burning fire. On normal conditions burning a cubic feet of dry firewood will keep the Pystyuuni warm for 24 hours or longer.

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