I just completed a large 9’x12′ sauna at Silverlaken Glampground near Letchworth State Park. The glampground is an ideal setting for quiet retreats or group gatherings: a main lodge in a historic cottage, private cabins and luxury tents next to sparkling Silver Lake just miles from one of the most popular state parks in New York. The sauna is the perfect centerpiece for small or large gatherings. A group sauna is different from a small intimate home sauna; it creates a unique social situation where you can commune with strangers and make new friends all while stripped bare of the trappings of social status, class, or superficiality. It can be a perfect setting for friends to solemnly celebrate life’s important moments: a reunion, a wedding, a men’s retreat, or whatever occasion that will be enhanced by closeness and shared exhilaration. The sauna easily holds a dozen or more bathers and is a stone’s throw from the lake.
As I always do, I tested the sauna before leaving a finished project. The new owner was elated as I brought it up to temperature and explained the intricacies of sauna; after a round, we jumped in the brisk lake. It was the perfect way to end an exhausting effort and make my long haul home a relaxing one.
If you are in Western New York and looking for a unique place to stay and want a sauna experience, I recommend you check outSilverlaken!
The kiuas, or heater, is the heart of the sauna. In a wood-burner, it is commonly referred to as the sauna stove, but a wood stove it is not! There is a lot of misconception around the kiuas and how it is different from a wood stove that you might use in your house.
First, some history. The modern house stove is really a heating device designed to add comfort to your home while conforming to certain safety and smoke emission rules. Typically they are not used as primary heating appliances, unless you live in a cabin off-grid somewhere. Back in the 70s, during the energy crisis, woodstoves became popular as a way to save money. They were pretty much unregulated and varied in design from a kit that consisted of a door and a flue collar you could slap onto a used fifty-gallon drum, to a more complex Vermont Castings wood stove. Earlier stoves had little control over combustion; these evolved into airtight units that could keep a fire smoldering all night, if not for an entire season. I had one of these highly efficient stoves and didn’t let the fire go out all winter except to clean it. Cleaning the chimneys on these units is an imperative: when wood—especially if it has not been cured for two years—is burned slowly by reducing the combustion air to near nil, creosote forms. This is the result of the wood’s resinous gasses condensing on the inside of the cool chimney walls. As a result of the slow burning, these stoves emit a lot of smoke. After many houses were lost to chimney fires, safety regulations were put into place, and stoves are now required to use catalytic converters to reduce emissions, much like on your car. These regulated stoves require a religious adherence to the use of dry wood, lest your catalytic converter clog up, which they tend to do. Such stoves evolved into today’s models that use a carefully designed system of baffles and airflow to make fires burn efficiently. Now, all wood-burning home heating devices installed in the US must comply with UL (Underwriters Laboratory) safety standards and increasingly stringent EPA standards for particulate emissions. The stoves work well and are very cozy but, by design, they heat up slowly and are not meant to burn all night long not to mention all season long. Because they are intricate designs with interconnected parts, they are all cast iron. The exception is some stoves made in the pre-catalytic converter era, which were welded steel.
So, that is a wood stove. You may find a used one and think you can build a sauna around it, but the truth is, with the rare exception of one of those 70s all welded steel stoves (not the barrel ones!), you can’t. You can build a small hot room with a wood stove, but it will never be a real sauna. Here is why: A sauna stove, or kiuas, is designed to do one thing—heat sauna rocks. It is the hot rocks that heat the sauna and produce bursts of löyly steam, the essence of sauna. Early saunas did not have metal stoves. They did not even have the technology to make a metal stove, all they had was wood, earth, and rocks. The kiuas was essentially a hollowed out pile of rocks that lacked a chimney. A fire was lit within, the room filled with smoke, and after the rocks got hot, the fire was extinguished and the room cleared of smoke via vents and thereafter the rocks heated the room. The closer you can get to that smokey ideal—Savusauna experience—the better.
A sauna stove is not a wood stove; it fires hot and fast, it burns sticks not logs. Its job is to heat rocks. If fired correctly, you will never have to clean the chimney. The appropriate hot fire will combust all of the sticky wood gas and reduce creosote buildup. It is welded steel—can stand up to having water poured over it while red-hot. Cast iron cracks or explodes when subjected to this. It can take the weight of a hundred or more pounds of rocks sitting on top of it when cherry-red. Ferrous metal takes on specific colors when heated. At 1400° F, it is cherry red. At that temperature, an 1/8 inch plate of steel is as malleable as taffy on a hot summer day at the beach. I’ve repaired many sauna stoves with tops that looked like an egg carton from the stones pressing down on the hot metal. So I started making stoves (my Lämpimämpi sauna stove) with 1/2 inch thick plate at the top. I fire my stove so hot that I see dark, cherry-red glow underneath the stones. I swear that sometimes I can read a book by the glow coming off my sauna stove. If you fired your home-heating wood stove like that, you would be crazy. I like to test the limits of my stoves to know they are safe.
When you light a sauna stove, you want to fire it, that is, bring it up to temperature quickly. Use paper and dry kindling and then stuff it full of sticks, not logs (wood scraps from building saunas work great). Because sauna stoves are for intermittent use, they are exempt from the EPA particulate rules. But, the truth is once it gets going after about ten minutes, it should burn so hot that there is no smoke at all. Other than the shimmering light from the escaping heat, I can’t tell if my sauna is heating up by looking at the chimney. House wood stoves are tame devices, meant to be safe. Sauna heaters are another beast. That is why I will never install a wood-burning kiuas in a sauna in the home or attached to a house. Wood-burning saunas do burn down now and then.
If you are building your own wood-burning sauna, you may have a building inspector involved or have to get a wood-burning appliance inspection for your home insurance, and that may require a UL listing. The only heater with a UL label is the Lamppa Kuuma stove. Most others are made for the European or Canadian market, which use different standards. So, before you click on “buy” you should have a conversation with any inspectors involved. They may love the idea of a sauna, or they may think you are crazy to sit in a small hot room and throw water on a red-hot wood stove. In that case, you’ll have to convince the inspector that it’s something that’s been done millions of times without incident. In any case, you will need to make a safe installation of your kiuas. There are clearances and heat shields and floor hearths, none of which can be cheated on, unless you don’t mind owning one of the saunas that burn down. There is also combustion air to consider, which is why I like to fire mine from the outside. The sauna stove sucks up fuel and oxygen, so it’s better to not be sucking the air out of the tiny room you and your friends will be in. This is not such a problem with house wood stoves; although, it is an issue with newer air-tight construction and tiny homes.
So, before you purchase that old wood stove you find on Craigslist, do your research. Think hard about investing in a real sauna stove. The kiuas is not a wood stove. The kiuas is the heart of the sauna.
My stove pipe will get cherry red! After ten minutes, a hot fire should burn clean and smokeless.All stoves will smoke initially.Nothing bigger than your arm!This armload of ash will fire the sauna.Fill the stove and let it burn hot before closing the ash drawer.
My latest mobile sauna project started when a customer contacted me wanting a mobile sauna she could use for hot yoga (Bikram). It’s my standard 5’x8′ trailer sauna but without the benches. The arched roof allows for plenty of room for stretching out, and the floor is soft cedar. The heat comes from a Scandia propane-fired heater. It’s a cute little unit that weighs under two-thousand pounds. Tow it to the next yoga retreat and show off your downward dog.
When the client for my latest mobile sauna project contacted me, he told me he needed something that would look and feel like a sauna from back home in Finland. He wanted it to be wood-fired and to get really hot. He wanted the clean lines and rustic charm of Finnish design and even requested a traditional pine tar finish like what the Vikings used on their boats. As small as it going to be, it was to have the standard two rooms: the sauna room and a dressing room. He also wanted to use the latest solar technology to light it with a soft glow.
But working for an American company where he might get moved from time to time, he wanted it to be untethered to his house and portable, so he could always bring it with him like a cherished possession.
I enjoy challenges. In fact, I thrive on them. One of the advantages of having my own company is that I get to decide how much to put into each project and which projects to really focus on. On some projects, like this one, I get to expand my repertoire. The goal, as always, was to bring my client’s dreams into reality. The result did just that: a mobile sauna on a 81″x120″ trailer, under three-thousand pounds, with a dressing room, solar-powered lighting, custom wood stove, northern white cedar interior, and pine tar exterior finish. I created a little oasis—a reminder of Finland—that my client can park in his back yard. A dream come true.
Saunas are like that. When you have your own, it is a dream come true, a special place to escape into, to relax and unwind. Though tied to old traditions, for many, sauna is a new experience and can be life-changing. As designer and builder, I get to be the midwife for people’s dreams and help them usher in a new way of living or rekindle a past love. As we turn the page to a new year and think about resolutions, what dreams do you want to come true?
Mobile sauna by Rob Licht Custom Saunas.Solar powered lights on mobile sauna by Rob Licht Custom Saunas.
I get a lot of questions regarding sauna insulating details and thought I’d shed some light on a few issues. A caveat before I start: heat transfer science gets pretty complicated, and I am grossly simplifying things here. I’m not an engineer, I rely on experience and am constantly probing and measuring my own saunas to see what works. A building inspector may want an engineer’s input, but just make sure the engineer understands what happens in a sauna.
If you are building an electric sauna, either in your house or as a stand-alone building, you’ll naturally want to insulate it for efficiency. Normally builders (and building inspectors) think of R-value (printed on every insulation product label) as the golden metric, and the R-values of a wall assembly are typically added up to get a number that either complies with code or satisfies a self imposed trade-off between cost, efficiency and practicality. R-Value is the resistance to heat transfer. But it measures conduction and convection, not radiation, which is not much of a factor at lower temperature differentials. R-values are calculated with normal living spaces and long-term heat retention in mind, which in a typical home is calculated using an average temperature differential of 24°C (between heated and outside space). Since R= Delta T/QA, (where QA is the ability of the material to transfer heat) and in a hot sauna Delta T might be 100°C, the use of labeled R factors is totally skewed!
The second factor is time. Heat loss is measured in BTU/hr. With the sauna only on for a few hours a week (bravo if it’s more!), your heat loss will be minimal, and hopefully, in the cold months it will contribute to heating the house. So, in terms of cost vs. efficiency, a lot of insulation may be overkill.
At the higher temps of the sauna, the radiant effect of heat is more of a factor and the use of a radiant foil barrier comes into play. The heat you feel radiating from a wood stove is the long-wave radiation. This radiation can move through common building materials, but foil stops it dead in it’s tracks. Anyone who has nestled under an emergency blanket or protected themself from the fiery radiation of a blast furnace (like when I pour bronze), understands the effectiveness of foil to bounce radiation back towards the heat source. But if the heat source contacts the foil layer, the aluminum superbly conducts the heat, defeating the purpose. So, when building a sauna, it is the radiant foil layer with an air gap on the hot side that is crucial to holding the heat in. This should be backed by as much standard insulation as is practical, but don’t worry about attaining super R-value. The exception being if the wall is an outside wall of the house and a part of the building envelope. In this case, R-value must be a minimum of what the rest of the house has. I prefer mineral wool, but in any case, do not use XPS or EPS foam directly behind the foil, as they will melt at sauna temps!
Vapor control in an interior sauna is really important especially, in modern tight houses. These structures tend to trap moisture. Vapor can cause damage that you can see, such as peeling paint, but also damage you won’t see, like moisture condensing in a wall cavity. Radiant-foil barrier, when carefully taped at the seams, is also a perfect vapor barrier. When I build interior saunas, I think about all of that moisture and imagine where it can get to and wreak havoc. I then seal off those spaces, provide a vented path for moisture to escape. Some enthusiastic löyly action will turn ladles of water into steam, which fills the sauna and then escapes into the house—like when you forget a kettle on the stove and all your windows fog up. The best thing is to build your sauna next to a shower area and then vent that area with a decent bath fan to the outside or via the household HRV system. The sauna should also have an air intake under the heater, as per manufacturer’s instructions, and via a gap under the door so the sauna gets a healthy exchange of fresh air. Never connect the sauna directly to a mechanical ventilation system.
With careful planning of layout, insulation, ventilation, moisture control, and a heater that makes good löyly, your indoor electric sauna can feel like a wood burner on a pond’s edge and also be an integral part of your efficient home. (Read more about Radiation. Read more about building materials (including foam) at Sauna Insulation, Revisited.)
