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.
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’m excited about my latest project: a wood-burning mobile sauna.
Unlike all of my other projects, which I design and build to meet the needs of my customers, this one is for myself. Over the past five years, I have been without my own sauna. It’s a long story. Basically, I sold my house (and sauna) expecting to buy another and build a new sauna, but because the lending rules changed after the housing crisis, with a bias against self-employed folks, I have been stuck in renter’s hell. So, while my customers have been basking in the warmth of my creations, I have been languishing in a sauna-less purgatory, dependent on the generosity of my clients for the too infrequent sauna. Like the proverbial cobbler whose kids have no shoes, I have been the sauna builder without a sauna. For renters like myself, the mobile sauna is the perfect solution.
It is a 5’x8′ sauna built on a commercial utility trailer. It is lined with northern white cedar and fired by one of my custom Lämpimämpi wood stoves. It has an arched roof using laminated bent cedar supports and aluminum sheet. It feels a lot roomier inside than you would think and comfortably holds four people. And, yes, it meets the two-thousand pound gross vehicle weight restriction of the trailer, so it doesn’t require a huge truck to haul it.
I’ll use this sauna for promotion—look for it at various venues and festivals including the Ithaca Festival parade (Again! Our first mobile sauna appearance was back in 2014). I’ll be taking this one with me on vacation or to my favorite park or forest stop. So, if you see it, feel free to stop and ask me to show it to you. Who knows, if it is hot I might even have a few spare towels.
The stove, heater, or as the Finns call it, the kiuas is the heart of the sauna. The role of the kiuas is to heat the room. But not like a wood stove, but by heating the sauna rocks, which in turn provide the heat and the löyly, or steam, that make a sauna what it is. In the savusauna, or smoke sauna, which arguably offers the most authentic experience, there is neither stove nor chimney. There is simply a pile of rocks made into a hearth. A fire is burned within (filling the room with smoke) until the rocks are hot. Once the fire is extinguished and the room cleared of smoke, the pile of rocks does its thing. Likewise, any sauna, whether it is wood fired or electric, is only ready when the rocks are hot.
When building a sauna, the choice of heater is important. But the rocks are even more important. A good heater will hold a hundred pounds, and thus, will make good löyly. A cheap heater will provide a few decorative stones, and you will feel like you are sitting in an electric oven. I have seen many well-designed saunas in my years and I have seen many poorly built saunas, as well. The worst use some variant of a cheap wood-burning stove with a dented pot of rubble or brick on top. In the best, the rocks are the focal point, and they get red-hot. Pick one up (with heat-resistant gloves, please) and drop it into a pot of water and you can make tea.
Left: Rocks shipped thousands of miles—only to explode in the sauna! Right: Cayuga Lake beach stones—can you spot the erratics?
The type of rock is critical: they should be igneous in origin, formed deep in the hot earth or in the furnace of a volcano. Think of these rocks as heat loving. Granite, grabbro, and basalt are typical examples. The Finnish and Swedish units might use grey peridotite. Then there is shape: smooth and round potato shaped rocks or jagged and broken pieces. I prefer the smoother rocks, but there is argument for using the jagged (more surface area). You can order a box of the latter from Tylö that will come all the way from Sweden. Once I opened a box to find a nice hand-written note from the fellow who packed them. Another heater company sent me a box from their supplier in Central America. Apparently, they needed a geology lesson. The polished siltstone rocks, once heated, started exploding! If you don’t want to have a box of rocks shipped half way around the world or risk getting impaled by rock shards, you can find your own.
Unfortunately, our local stone, meaning the rock that is cemented to the landscape here in Central New York, makes horrible sauna rocks. It is all sedimentary: shale, limestone and sandstone. Born in the bottom of ancient oceans, these rocks do not love fire and will complain by exploding if thrown into one. By the way, baptism by fire is a good way to test your rocks if geology eludes you—a good rock will happily glow red-hot. Thankfully, the glaciers that plowed through here brought with them piles of stone from places north that serve the sauna well. These are glacial erratics. As the glaciers retreated and melted, these stones were left behind. The resulting floods that carved our landscape left piles of these smoothed rocks (mixed in with plenty of local stone) in deltas, drumlins or moraines. I find them in the local gravel pit, which mines an ancient delta, or along the lake at my favorite park (another delta) when the water is low. Sometimes I take milk crates with me when I travel through the Adirondacks and fill them with potato-sized anorthosite rocks—which is what the moon is made of—and other pretty granites.
More important than the geology is the significance of the rocks. A Finn, even if they are using a heater with rocks packed in Sweden, will add a spirit stone or two: stones that come from home or some other special place. Stones all have distinct place markers and are borne of this earth and tied to a particular landscape. Except erratics. These have been swept from their homes in a geologic diaspora and found new homes as immigrants, oddities, and beautiful accents against the dull grey of the indigenous rocks. Even though I am made of local stone, coming from generations of Central New Yorkers, I have always related to the erratics: the outsiders, the immigrants, the atypical people. They bring us diversity, new culture and traditions like the sauna. In my next sauna, you will certainly find plenty of erractics.
Redhot Adirondack rocks / My Lämpimämpi stove / Stove wall faced with local field stone including shale.
Finishing a job is always a sweet endeavor. I usually budget in one day of fussiness: A day when I can pay attention to all of the little details, get the stove in place, and then, as a last step, give the sauna a test run. This is when I get to see how my efforts have paid off and take note of how the sauna actually fires. Is it hot enough? Is it light and airy and does it have that right sauna feng shui? Does it reach a good temperature and would Ozzie—the Finn who started me on my sauna-building path—approve?
The job I just finished is a modest affair: bare bones, applying that Finnish sort of pragmatism. I converted a kit-built garden shed, the type you’ll find lined-up on the edge of a big-box home store parking lot, into a simple sauna with no dressing room. I liked the challenge of working within a modest budget, and I liked the folks: down-to-earth, modern-day Helen and Scott Nearing types. I had to remind myself that a sauna does not have to be a luxury item, affordable only by those in the higher income brackets. A sauna should be as essential and ubiquitous as indoor plumbing.
I lined the inside with knotty pine—a low budget alternative to cedar. Sitting on the top bench, I noted that the smell of pine reminds me of my forays into woods here in the east. It is a familiar smell, close to my heart, unlike the rarefied smell of cedar. Aside from the knots, which will forever bleed sap that will inevitably find it’s way into someone’s hair, it is a fine wood to use. It is not as stable as cedar, but the inevitable cracks will open the sauna up and let it breathe. We always said that Ozzie’s old sauna at Podunk, with its gappy, knotty-pine walls and sagging ceiling, felt better than any other.
MyLämpimämpi stove fired fast and hot. The rocks quickly reached good löyly temperature and the first splash of water had me moaning in ecstasy. At no point did I feel that claustrophobic locker-room-sauna feeling of not being able to breathe. The dual windows filled the space with light. The benches will hold the couple, their kids and several neighbors. In term of essentials, it is a perfect sauna. Nothing more is needed—no fancy tile or trim work, no designer dressing room. It works, plain and simple, and it works well. It was the best sweat I’d had in a while, and a good sweat is almost payment enough.
