The old sauna at Podunk had two rooms: a small dressing room and the larger hot room. The old Nippa stove sat between them, embedded in a masonry wall. Sitting on the benches we stared at the business end of the stove with its pile of rocks, and the stove was tended from the dressing room side.
This arrangement always made sense to me and is how I have been building my saunas for thirty years. I learned to weld in art school and set up my own studio soon after. Ozzie, the owner of the Podunk sauna, would send people my way for stove repairs. After seeing how other stoves failed, I designed and started making my own stoves using much heavier plate on the top. In the older stoves, the heat would soften the thinner steel and typically lead to collapse under the weight of the rocks. I also kept to the external feed (thru-wall) and designed my stoves to be fired exclusively that way. As kids, we loved to pretend we could speak Finnish by stretching vowels and jamming consonants together to make up Finnish sounding nicknames for each other. I called my stove the Lämpimämpi by combining Lemp and Memp. Finns will chuckle at this because it translates to warmer.
I called my stove the Lämpimämpi by combining Lemp and Memp.Finns will chuckle at this because it translates to warmer.
There are so many advantages of the external feed (thru-wall):
The fire-tending, and associated ash debris, is kept out of the hot room, and you don’t have to tramp in and out with your boots on to tend the fire.
Venting a small space can be complicated; a sauna stove requires significant combustion air which can create drafts, or worse, steal oxygen from the hot room. The external feed draws air from the dressing room or outside.
Any stove front requires thirty-six inches of clearance to combustibles in front of it. This can’t be mitigated by heat shields. This severely limits the layout of the hot room. However, it is easy to get three feet in front of the stove in the dressing room.
Any stove also requires a noncombustible hearth (stone) eighteen inches in front of the stove. Hot ash and coals falling from the stove are a major source of fires. In a crowded and dark sauna room, these hot coals can easily be overlooked, fall under duck boards, etc.
A flickering flame may be romantic site, but it is the soft heat off the rocks you want, not the searing radiant heat you get from sitting in front of a blazing fire.
Typically, the fire may be almost out by the time the sauna is ready. The rocks should be the focal point. Also, following the 36-inch rule above, you can’t have the stove front facing the bathers, unless the sauna is excessively big.
If you are providing a sauna experience for others, you can discreetly tend the fire without interrupting the bathers or invading their privacy.
The external feed or thru-wall stove heats the dressing room just enough to allow hanging out and watching the fire while the sauna heats up.
Installing the external feed may seem daunting, but it is not that difficult. A firewall with the requisite size opening will be required. This can be achieved in different ways: solid masonry, which will add thermal mass (the sauna will take longer to heat); or a hollow insulated firewall with steel studs and cement board, tile or stone facing or stucco over metal lathe (which I typically use). A metal sleeve will be provided with the stove to dress up this opening and provide further heat shielding. My Lämpimämpi stove has an integrated heat shield/rock basket that works with the wall opening so that fresh air coming in is heated directly by the stove and directed over the rocks. This is an advantage over simply having the rocks sit on top inside a steel box. As with any installation, all listed clearances need to be adhered to, but with this method, the stove will take up less space in the hot room and make for a cleaner presentation. For your next sauna, consider this traditional, thru-wall approach to situating the stove.
Fire, like sauna, is a keystone of my life. There is a mystery to fire that even science cannot unravel. It is more like the fourth state of matter—plasma—than the familiar trio of liquid, gas, and solid. I have played with and studied fire since I was a kid, sometimes barely avoiding serious trouble, other times under the guidance of elders like in Boy Scouts when my troopmates and I boiled a quart of water in five minutes during a fire-building competition. As I grew to an adult, burning wood became a way to heat our family home. Wood cutting and splitting became not only a chore but a workout and a way to get my angst out with each strike of the axe.
After I learned metalworking in art school, I started to apply my skills to making wood stoves and thinking about what happens inside a stove—the mysterious process where tons of fuel wood are reduced to a small amount of ash, carbon dioxide, particulate, and other emissions, carried away by the wind. The heat is generated when the atomic bonds of carbon molecules break, turning matter back into the energy of the sun that formed those molecules. There is something seductively simple in that balance of carbon in/carbon out, but as we now know, there is also something deviously complicated about the carbon cycle. I have warmed myself with wood heat over the years in my home, shop, and sauna. Each time I light a fire there is still a allure to the flames that draw me to them, calms my mind, and perhaps blinds me to greater issues.
In the past fifty years, wood stove technology has gone through several changes. Initially, stoves were simply boxes with a loose-fitting door and a chimney—like the Ben Franklin stove. These stoves burned uncontrollably and inefficiently and needed constant feeding. Later, airtightness became a thing: dampers were dialed in, rope caulk was added to the doors, and the fires were slowed down so they could burn all night.
But while the fire burned longer and cooler, not all the organic matter was combusted—more went up the chimney. Flammable wood gases called creosote condensed on the cool sides of flu pipes and chimneys, building up thick tar-like layers. Eventually, that compound would catch fire, sometimes taking the whole house with it.
In the ‘70s, the nation endured an energy crisis, and wood stoves became a very popular way to deal with the spiraling cost of oil. The ‘70s also saw the birth of the environmental movement and the Environmental Protection Agency (EPA). The EPA stepped in to regulate the developments in wood heating as did Underwriter’s Laboratory (UL). Stoves had to be made safer and cleaner burning. Expensive catalytic converters—like on your car—were added to the stove outlet to capture some of the nasty stuff. But neophytes, in their craze to burn wood, skipped the all-important step of letting firewood dry at least two years. The converters clogged up. The cats were dropped, and the focus turned to better engineering. Stoves are now designed with all kinds of baffles to get the wood to burn cleanly. They are complicated affairs, and many don’t work that great. They certainly don’t burn all night, or as I used to do with mine, burn non-stop all winter.
But sauna stoves are different beasts. Since they are “occasional use only” (only one model is UL listed) they are, thankfully, EPA exempt. Technically. But still, I don’t want to be that guy who smokes out the neighborhood every time I light my sauna—especially since this past summer when we all got a taste of the Smoke Armageddon coming down from Canada’s forest fires. So, despite my years of wood-burning experience, I continue to tweak the process and learn the idiosyncrasies of my stove. Every stove fires differently, and even a familiar stove can rebel when the wind changes or when a sauna is moved. When I light mine, I know it will smoke some. My goal is always to get it burning hot as fast as possible so combustion is near complete and the smoke will be minimal.
The three sides of the fire triangle are heat, fuel, and oxygen. A perfect balance gives a cleaner burn.
You can easily adjust the fuel and air, but the heat, not so much. The heat in a wood stove comes from the fire itself, so you need to get the stove very hot, as quickly as possible, to achieve a good balance. Above a certain temperature, wood emits gas when heated in a reduced atmosphere; this gas will burn cleaner than the wood itself. If you get your stove so hot that the wood gas burns before the wood, it will burn cleanly. (There are cars designed to run on wood gas. A heated tank of wood chips creates the gas to power the engine.)
Most stoves have a baffle or two and an upper chamber where the hot gases will hopefully combust when mixed with additional air. The real heat is at the top of stove, before it exits the flu. In my Lämpimämpi stove, the top plate that the rocks sit on is 3/8” steel. I will get this steel glowing a dull cherry red (about 1300°F). Any gas passing through this chamber will be burned. But until the upper chamber is hot, gases and particulates will escape up the chimney, and the sauna will smoke. Having a brick-lined fire chamber will help the fire get hotter faster. Wet cool days will make it worse as will a down-draft caused by the sauna being in the lee of nearby trees or structures. Wet wood doesn’t help either.
Up until this week my process has been to get a small fire going briskly, with the ash drawer open and stove door open until it starts to roar (I have an external feed, so no worries about embers falling out). Then I add larger sticks in one or two loadings until I fill the fire chamber (nothing bigger than my arm–scrap 2×4s are perfect), topping it with one or two small hardwood logs. The problem is, when I add the fresh wood on top of the fire, there is a period of incomplete combustion as the wood heats up, and the stove smokes a lot. If the wind is wrong, my neighbors will get smoked out. I tinker with the ash drawer or open the stove door to blast in more air until the smoke clears (another advantage of an external feed: I can watch the chimney.) I can add more air to balance the fuel, but I can’t add more heat. Think of it like the carburetor on an old car. Too open, it won’t run well, too closed, it sputters and smokes and clogs the engine. Not enough heat, and it won’t burn well either. I try to find the sweet spot. Unlike a wood stove in a house, I’m not worried about things getting too hot (better than too cool). It’s not uncommon for my stove pipe to glow red for a while, but that’s ok, because I know my installation is safe.
Recently, after reading an online post, I tried a new way to fire the stove (yes, old dogs can learn new tricks): from the top down! I load up the stove with thicker sticks at the bottom, then smaller, with short sticks crisscrossing between them. Then on top of this stack I put wads of newspaper with a handful of kindling and light that. The fire immediately starts heating the baffle and upper chamber as the fire slowly works its way down. This way the flames aren’t cooking the larger sticks before they are ready to burn. This solves the too much wood/not enough heat problem. Amazingly, it only takes five to ten minutes for the fire to reach the bottom, and a hot bed of coals forms quickly. I leave the ash drawer open slightly for twenty minutes and then add more wood. After that, I can’t see any smoke. When we take our sauna to one of the local parks, we can be clandestine; with no tell-tale smoke, passersby have no idea that our sauna is cranking hot inside.
I know there is a whole argument for decreasing our carbon footprint as much as possible and not burning any wood, but there is an opposing argument that says we need to maintain our ties to nature to want to save it. Controlling fire is not only as old as humankind but one of humanity’s defining traits.
Without getting into the debate, which I don’t lose sleep over, I admit again that I don’t want to be that guy. I want to remain sensitive to others and burn my stove as cleanly as I can. Learning how to master the art of fire building is one small step to take if I am going to cling to tradition and enjoy a really smokin’ hot sauna.
We just finished this sweet sauna: an 8’x18′ building with an ample dressing room, large hot room, and wood storage on one end, all on a 12’x20′ raised deck. The site is near a cabin and a lovely pond, all on a remote hilltop in the Finger Lakes.
The design and the craftsmanship are driven by the concept: a weekend retreat from the bustle of life, removed from technology and the stress of the twenty first century. Nestled in nature, the sauna has windows to let the light in and open the view to the woods and pond.
We kept it simple yet well-crafted and elegant. The sauna functions as a centerpiece to the family gathering place and also serves as the bath house—the owners are eschewing modern conveniences like running water.
Henry David Thoreau may have had his pond, but what he really needed was a sauna.
If the heart of the sauna is the kiuas, or sauna heater, then the soul is the rocks.
Every brand of sauna heater I’ve installed has a different approach to the rocks. Some, like a wall hanging six or eight kilowatt unit use less, maybe forty pounds. And some, like the Harvia Cilindro or Club heaters use more, up to two hundred pounds. Wood burners vary too. Kuuma’s heater takes one hundred fifty pounds or so, but you have to provide your own. My custom-built stoves (Lämpimämpi brand) take a similar amount of stones and like the Kuuma stove, the rocks are piled on top, mounded as high as you can. The Harvia Legend, an elegant wood burner from Finland, has a basic cage surrounding the stove. By the time you are finished loading the stones, you won’t see the stove. There is also an optional cage that surrounds the stove pipe that hold even more rocks.
The Finnish and Swedish heaters use olivine diabase or peridotite, igneous rocks found in Scandinavia. The rocks I have used that come with the electric heaters look the same: grayish chunks, some flatter, some chunky, all in the size range you’d find in a bag of potatoes. These are amazingly cheap, considering that they come all the way from some quarry in Finland or Sweden. The UPS driver stopped asking what was in the boxes (“yup, rocks”). Once, I found a note in one from a young Swede, hoping that I was happy with my rocks.
My favorite rocks are hand-selected glacial erratics: various igneous granitic and metamorphic stones that I find in places where glacial melt waters sluiced out potato-sized rocks.
These are heavier and denser than our native shale, which is worthless for the sauna since it tends to explode when heated. The erratics have a crystalline structure that you can usually see and a solidity and heft evident when you pick them and bang them together (they are not easy to chip).
My favorite rocks.Lämpimämpi with glacial erratic rocks.Lämpimämpi with jagged olivine diabase rocks.
A significant consideration when selecting a heater is the rock capacity. The more rocks, the longer you should let your sauna heat up. Clients always ask: “How long should we let it heat up?” While I usually say, “About forty-five minutes,” I really want to answer with the same sort of retort I give when someone asks how long it will take for paint to dry (“as long as it takes”). The correct answer should always be: the sauna is ready when the rocks are hot enough to produce good löyly or steam. Löyly is the soul of the sauna’s mysterious expression. And how hot is that? Four hundred fifty degrees Fahrenheit, more or less. If you want more steam, then you want more rocks.
Löyly is the soul of the sauna’s mysterious expression.
More rocks are good If you expect several rounds or people coming and going. No one wants to pour water on the rocks expecting a stimulating burst of steam (but not too sharp), only to hear the fizzle of water barely boiling. That’s like trying to make an omelet in a pan that is barely hot. Disappointing, to say the least, but also bad for the heater. There’s a Finnish saying that goes something like this: when you leave the sauna, put another log on for the sauna elf, or he will pee on your stove. Which means don’t keep throwing water on the stove, especially at the end, if the rocks are not hot. The warm water will just sit on the steel stove and rust it. When you throw water on the rocks, it should all turn to steam, and when you are done, the stove should dry quickly. When I finish eating my omelet, I rinse my cast iron skillet and let it dry over the flame; I don’t let it languish all wet in the dish rack. The same principle applies to the sauna stove.
Jagged rocks will catch and momentarily hold more water, allowing less to get past the rocks and into the heater. The dense, roundish rocks I use produce a nice soft steam, but they have to be hot. I’m not so worried about water getting down to my stove, which is always very hot. (Lämpimämpi stoves have 3/8” steel plate on top so they will never rust out.) By the way, always use clean water and be wary of city water with chlorine or even country water with minerals or methane. We use only use filtered water or rain water for löyly at home. Spring water or distilled water might be prudent in some cases. Never use pool water or, worse, let some disrespecting novice wring out their bathing suit over the rocks, as I have seen in a gym—pleasant smells should emanate from the rocks. Special sauna oils or even Sauna Brew can be added to the löyly water for aromatic effect. Heck, we used to add beer to the water (cheap lager was always best).
Custom sauna with Harvia Cilindro and carefully placed olivine rocks.
If your electric heater comes with the jagged, grey olivine rocks, I suggest using them. They are selected to fit between and around the elements. When setting the stones, first I rinse them, then I take care to arrange the rocks one by one. It can take me forty-five minutes to fill a large capacity heater. For the Cilindro, I place large rocks at the bottom to hold up the others and then work a flattish layer against the cage wall. I then backfill against the elements with smaller and irregular rocks. On the smaller, wall-mounted units, I try to fit the flat stones between the elements without forcing or bending them. The goal is to loosely fill the cage so there is good airflow and to completely conceal the elements. Lastly, I top off the heater with larger stones and try to arrange them so they will catch water and force it inward, not splashing it out. In Finland there might a “spirit stone” placed here: a special stone or stones from a favorite place (make sure it is igneous or metamorphic—test it in a campfire first if not sure). The top might even have a layer of more decorative stones, which in Finland you can buy from sauna dealers, but here in the US, I have only seen the same dull grey stones. The Harvia web page has a good section on stones and how to place them into the pillar.
Once you have the sauna going and have been using it for a year or so, expect the stones to settle and flake off. You should remove them, vacuum out the heater and replace the rocks loosely, discarding the broken ones and adding more if needed. Failure to do so will cause the heater to eventually overheat and lead to the elements failing.
Care in selecting and placing the rocks will ensure that your sauna…Rocks!
All summer long, I have eagerly anticipated this week. I have a cottage rental on the lake. It’s the highlight of my summer, and a much-needed break from all of the projects I have going on. This year, in addition to the usual activities—swimming, canoeing, beach fires, collecting beach glass, and just staring into the waves while sipping wine—I’ve added one more Sauna! I’ve brought my wood-fired trailer sauna with me and parked it ten feet from the water’s edge. Nothing beats coming out from the hot steam of a good löyly and jumping into the cool, refreshing lake. It is perfection.
Mobile Sauna by Rob Licht Custom Saunas on Cayuga Lake
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