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Wood burning sauna: feed from the outside or inside?

When designing and building an authentic sauna, the question of inside feed or outside feed comes up a lot.

SHORT ANSWER:

I recommend feeding wood burning sauna from inside the hot room.

Reason #1:  heat loss

There will be 25% heat loss from feeding a wood stove from the outside.  This is not my figure, but confirmed by Daryl Lamppa, 3rd generation Finnish sauna stove maker.  The front of the stove is thee hottest.

Reason #2: cost

If building a sauna with feed through a wall, it costs $500-$1,000 more in materials, as code requires metal framing and clearances to non combustibles.   Plus there is the intangible cost of concern to frame a stove inside a wall.

Reason #3: ambiance

A glass window helps create a warm glow vibe, gently dancing off the cedar walls.  Ahhhhhh.  What about the mess from feeding wood from inside the hot room?   No big deal.  Get a hand broom and sweep it out once and awhile.

Hi Glenn,

I discovered your site and appreciate all the information you have here–I discovered that we have a great sauna stove mfg. right here in Minnesota–so that was good to learn.

I’m dreaming of building a wood burning sauna, so I’m looking at floor plans. I see one plan you recommend is to have the stove at the rear wall, centered in the sauna. Does this mean feeding the stove from the outside?

I was in a sauna this fall that had a changing room, and you fed the stove from that room. That seemed like a good idea to me, because the stove was inside…any particular reason for not feeding the stove from the changing room? Maybe it’s better from outside, so you have more room and less mess in the changing area?

Just curious about your thoughts on this as I start my research.

Thanks,

John
St Cloud, MN

Hi John:
Glad you found the site, and glad you find it useful.  it’s nice sharing the joy of sauna.  I particularly enjoy building saunas as you can see.
With regard to feeding a wood burning stove, i am a big fan of feeding from inside the hot room.  In the old days, an outside feed made sense because sauna stoves were not very efficient.  It became a will of sorts, overcoming inefficiency with more logs, stoking the heck out of a barrel stove or home made contraption.
The feed from changing room is a viable option.  It saves a bit of space, and offers heat into changing room.  In my experience, however, this is unnecessary.  Heat gets in the changing room just fine by opening and closing the hot room door.  Further, feeding through a wall requires some elaborate fire proofing and framing around the “throat”.
Today, wood burning sauna stoves are very efficient.  I can start and take a sauna with a handful of firewood tucked under my arm.  Loading from the hot room has never been much of an issue for me.  BONUS:  many wood burning sauna stoves, Kuuma included, offer a glass window.  A wonderful aura, turning the light off in the hot room and seeing a warm glow reflecting off tongue and groove cedar in the sauna.  Magical.
Hope this helps, please stay in touch.
g.

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35 Comments on This Post

  1. Glenn – you’re a great resource; thanks for all the good work you do. I’ve built a couple saunas (I’ll send pics one of these days), and I’ve fed it from outside and inside. They both have pros and cons – feeding from outside keeps the sauna cleaner: you don’t have any of the ashes or dirt that comes off the wood. You also don’t get any smoke in the sauna. The major disadvantage is that you don’t see the fire. There is something elemental about sitting in a wood fired sauna, watching the flames, having the gentle light of the fire in the evening. It is also more difficult to gauge whether the stove needs more wood. Having done it both ways I’d probably stick with having the stove in the actual sauna. Just my 2 cents.

  2. Glenn
    I have never had my own sauna but have decided to put an outdoor sauna on my property. Not sure if i will build my own considering my skills but i hsve looked at some barrel saunas. I would prefer wood fired and have noticed that their are a couple different builders in minnesota. Any insight to the barrel sauna? Electric vs wood. Load wood outside or inside?

    Mike
    White bear lake mn

  3. John, I’ll offer my opinion, too. I went with the inside-the-hot-room-feed Kuuma wood stove (partly on Glenn’s recomendation and partly on the stove maker’s (Daryl Lamppa). I’m very satisfied with the decision. I bought a small shop vac (fits under the change room bench!) to clean up any dropped ashes and my stove has the optional ash drawer, so clean up is fairly easy and mess free. The in-room stove captures all the heat and with a window on the door of the stove, you get can enjoy the reflective flicker of the flames from the benches. I opted for an electric wall heater in my change room, so I have no trouble with heat in either room. As Glenn advised me–“You will only do this once, so do it right the first time and you won’t be sorry”

  4. Hi, I am in the planning process of building an outdoor sauna from scratch. I have wood working skills, and the project seems pretty straightforward. I would like to a build a sauna room that is 6x4x7 (this is not including a gabled roof). That would put the interior heated portion of the structure at 168 cubic feet.
    The issue I have is finding a wood burning stove rated for 168 cubic feet. All the wood buring stoves I have found seem to start at 218cubic feet or higher. Any suggestions?

    Please let me know.

  5. I am building a wood sauna stove to place in a barrel sauna. Half will be inside and half out. The insulated chimney will be placed outside top between the end where the feeder door is and the sauna wall. What do you recommend in inches should the chimney be placed away from the sauna wall?

    Thank you,
    Tom

  6. We built a wood burning sauna with back door feed. It keeps smoking inside the sauna. Smoke leaks around the chimney inside and very little comes out the top of chimney. Do you have any suggestions?

  7. Yes, Ann. You’re not getting a good draft. Something is constricting the air flow up your chimney. I’d get up on the roof with a flashlight and take off the chimney cap and look down into the chimney pipe and see if there’s anything going on in there, like a birds nest or whatever. Then, with the chimney cap removed, light a fire with newspaper or birch bark and see if that helps, as often the chimney cap can get constrained, especially if it has mesh around it for birds and bats and such. If this gets you nowhere, disassemble the black stove pipe just above the sauna stove and clean out that area. And if you’re not venting straight up through the ceiling but have elbows and such, well, this is a whole other diagnosis for another day. Hope this helps!

  8. Hi,
    I am planning to build a small sauna room outdoors, and plan to construct a smallish wood-burning pizza oven, dome-shaped but elongated design, with the back of it protruding through the wall of the sauna. Instead of rocks, I plan to sprinkle water directly onto the refractory bricks. The oven will be fed from outside, and the chimney will also be outside, close to the mouth of the oven in typical pizza-oven style. Will this work? I suppose the oven will have to be fired up at least an hour before using the sauna.

  9. Bruce, As a big fan of wood fired pizza as well as wood fired saunas, I applaud the thinking.

    But i’m fuzzy on this plan. Not sure how well this structure can provide adequate sauna heat. Tossing water directly on the bricks (vs stove rocks) may not provide the kind of “ahhh” that one enjoys during the traditional, authentic sauna regimen. If it were me, i’d build the sauna with a wood fired sauna stove, then sit on the sauna bench and think out phase II: you’re wood fired pizza oven as a separate unit.

    Trying to do both in one structure may end up being like trying to design and build one boat that is both a canoe and a pontoon. Both get compromised and you have to paddle too hard to fully enjoy either.

  10. Hello ,
    I was wondering do I ever have to clean our my sauna stove pipe. I bought a,stove from yowhat is best wsu and it works great. Should I worry about cresol build up ? I burn dry ash and dry pine mostly. What is best way to clean and how often ?

    Thank you,
    Mark

  11. Mark:

    Yes. I don’t know what “youwat” stove company is, but cresol build up is scary stuff. I’ll be candid in that i’ve never cleaned out my cabin Kuuma stove pipe. The stove burns super hot and no smoke, so no cresol build up. I suggest googling cresol build up and work on a method for cleaning out your chimney to your sauna stove.

  12. Glenn,
    I would like an update from Bruce – Bruce says
    September 9, 2016 at 3:56 pm. Pizza Oven fed from outside w protruding into Sauna for heat? Did he come up with anything that would work as a hybrid – as I have been thinking the same thing?

  13. Peter:

    Short answer: You can use an indoor woodburning stove as a sauna stove, but I wouldn’t. Indoor wood burning stoves burn differently. I can’t explain it but they do. And what is most critical is hot sauna rocks. You can try welding a basket and loading a bunch of sauna rocks on top of your wood stove and many do this. I have never been in a sauna with this set up that works well though. I am a big fan of investing $1k into a kick ass authentic wood burning sauna. A stove like the Kuuma was tinkered and engineered during -60f Minnesota winters. It’s built with 1/4 inch steel and is engineered to burn super efficient. And the chamber to hold rocks does just that. So, that’s my take Peter. Hope it helps.

  14. Excuse my ignorance, but what is the water chamber on a wood-burning sauna stove for? I have always been in saunas with rocks on top that allow us to pour water over them, to create steam. Why would you need a water chamber inside the sauna?
    Thanks

  15. Lots of saunas at lake cabins, hunting shacks, and rural areas have a water tank on the side to produce hot water for bathing.

  16. One advantage to feeding the kiuas from the outside or the dressing room of a sauna is not bringing in wood debris and associated dirt on the sauna floor. One of my friends feeds his stove from the back covered deck of his sauna which is accessible from his dressing room via a covered side deck.

    That being said, feeding the kiuas from inside the sauna is fine and most common.

  17. I was convinced when building my sauna that I was going to load from the changing room. My wife insisted on a stove with a glass door and loading from the inside. I’m really glad she changed my mind. I really like the setup we have.

  18. Yes ,I agree with your wife and the glass door. It is reason #3 for feeding wood stove from inside the hot room, and it may in fact be reason #1 on a cold winter’s night while the warm glow dances off the cedar walls.

  19. Not going to debate this as it’s only a personal preference. However the firebox on that stove (pictured) looks awfully small. Seems like a pain to keep a hot fire going when only kindling can fit inside that clearance.

    Also, I do hope you omit infrared from your websites dictionary. It has no place or relation to any wood stove or electric sauna. It evolved that way because marketers didn’t know what else to call it. For people looking for stoves and infrared is ever mentioned, run away asap. The dealer knows nothing about saunas and is just selling you garbage.

    http://www.finlandiasauna.com/sauna-faq.html

  20. Eric:
    Firebox from sauna in photo: That stove takes full 16″ logs. I don’t work for them, but own two of these stoves for each of my two saunas, and am also bent on the personal preference of being able to take a hot sauna only with a reasonable stack of cord wood brought in to the hot room tucked under my arm. (4-5 sticks). Like you, I feel the pain for those trying to keep a good fire going and heat maintained with one of those cheesy stoves shoehorned as a sauna stove. We build our saunas one time, we owe it to ourselves to use a kick ass sauna stove.
    Infrared: Helping others navigate away from such a shitty abomination remains one of my deeper passions vis a vis AUTHENTIC sauna. I will continue to write about infrared light bulb closets. Well put about its evolution. I offer free sledgehammers to those who make the conversion. “the best art divides the audience.” https://www.saunatimes.com/building-a-sauna/infrared/

  21. I know you respect Darrel, but we have a problem with your statement about heat loss. No way is there as much 25% heat loss, matter of fact there is less on an outside feed stove. The front of the stove by the door is the coolest spot , not the hottest as was said. The air intake is there and the incoming air keeps it cooler. The hottest part of any stove would be near the exit from the firebox to the chimney. I have taken temperature readings all over and around installed sauna stoves while fired up hot.
    Any stove needs air to burn. This incomming air will come in from outside one way or the other. That will cool the sauna if the intake is in the sauna. A good stove will not need to be fed while taking a sauna for say one hour, no need to add wood durring. Building a fire does take two feedings, no sense at all to open your sauna door for that, you will just cool it down.
    Also you mention efficiency, a sauna stove burns effeciant just by the fact that it is burning hot. You can see this by the lack of ash left after many saunas taken. Darrel has done wonders to build effeciant home heating stoves , but any efforts to reburn left over gasses are wasted on a hot fired sauna stove. There are no left over gasses. If only he could achieve the total burn of a sauna stove in a heating unit.
    I’m pretty sure you won’t post this and I don’t expect you will.
    Anyway sorry to disagree. Have a good day. Owen

  22. I have a main sauna at my house…pentagon shaped….lrg inside feed stove with glass doors …the sauna is 122 square feet…..I have a water system in my sauna. ….a tank sits behind the stove and a mixing valve adjust the temp for shower outside….plus I have a sauna on wheels I pull behind my quad right on the beach beside the ocean…im gonna build another sauna at my float cabin

  23. Hi, Thanks for all the comments and info on outdoor and indoor feed of a wood burning Sauna. I am building a Sauna in New Zealand were cedar wood is very expensive. I think that is it all imported. I am would like to know if a wood called Marcocarpa will be any good to use for the inside of the Sauna? It has a natural preservative in it and does not need treatment when used for ordinary building. Thanks Tony

  24. Tony: preservatives, whether natural compound or chemical based, are not good for hot room. Avoid any such shenanigans. Yet, when you say “natural preservative” I know you are referring to how, like cedar, the wood itself does not rot as its natural habitat is heavy with moisture, etc. With regards to Marcocarpa species, please forgive, as not only have I not heard of it, I can’t spell it, and if forced to guess what it is, i’d probably say it’s some kind of fish species instead of a wood species, so long way of saying sorry, I do not know. Mebbe you can call the Melbourne University Forestry Department and get them going on your question. It’s interestingly cool how wood species, (like fish) are inter related as cousins, etc. as far as properties, etc. Tony, also, I hear you on looking to save coin with wood in your hot room. On that score, check out this post:https://www.saunatimes.com/building-a-sauna/money-saving-tips-for-building-your-own-sauna-wood-paneling-for-your-hot-room/

  25. Hi Glenn,
    We’re building an outdoor sauna & trying make a final decision on the inside/outside feed… I know the pros & cons as I’ve stoked many of both…
    my question tho… we’re trying to decide if the location of the sauna (compared to house) matters as far as the direction of most common wind and smoke goes? Thinking to put sauna NW of the house, but that we’re most common wind in MN is… should it be in another direction? Or is this a matter of getting a good stove, chimney & type of wood you burn? We’re hoping to not get smoked out in the house! Or just skip the wind direction idea and build it where there’s nice privacy and seclusion? Thanks!

  26. Jeff. You answered your own question, and here’s your answer:
    This a matter of getting a good stove, chimney & type of wood you burn.

    I’m 100% confident that if you follow above, that you will be fine. After lighting either of my wood burning sauna stoves, after 5-10 minutes, it’s hard to tell if it’s going or not. One has to look for the heat waves emanating from the chimney. And another thing, this efficient burn means less wood needed for a good hot sauna session. This innovation has allowed for sauna stoves (with glass window) to work perfectly awesome with inside feed. And another thing, inside feed means 20-25% greater efficiency, too.

    Lots more on this on saunatimes. You can learn a lot about wood burning and “gasification” via the Daryl Lamppa Sauna Talk or searching some of these relevant terms on this website. Glad you asked, and hope this helps.

  27. Hello Glenn;

    Thanks for this web site! I just donated $20.00 via PAYPAL for your ebook. My name is Dave Shattler, e-mail is w……comcast.net Planning on a 14X8 building with a 8X6 “hot room” and a 8X4 changing room and a 4 foot porch for cool downs. Live just outside of Lansing, Michigan. Address is … Grand Ledge, Mi. 48837.

    I know you like Kuuma wood burners, but do you have any comments on the Superior Sauna KARHU 16CK With Glass Door? Attractive price, and it looks like it will be just right for my size sauna. I will start building as soon as I can pour the concrete piers.

  28. Dave: Great to visit with you. Glad the book is “exactly what you’re looking for.” What an amazing story, and excited to share the details of your build via a guest post on saunatimes. You will be just fine with the Karhu, given that you are building your sauna with so many of the critical/right elements in place:
    well insulated
    changing room
    vapor barrier
    decent, well aged and dried wood (ash!, maple!)
    etc.

  29. I way prefer an outside feed. Way cleaner. No smoke and no muss to clean up inside the sauna. Might not be as efficient, but I feel that feeding the stove is almost as much of the sauna experience as the sweat itself. It is part of the ritual, not a chore.

  30. Hey Glenn,

    Looking to build an outdoor sauna with my father this spring/summer. He wants to set up an inside loading wood stove. A neighbor raised a safety concern saying that you run the risk of running out of oxygen with an inside loading loading stove – how much truth is there to this? Does it come down to the type of stove you are using?

  31. Dylan: If it were true that you can run out of oxygen with an inside loading stove, i’d be dead a long time ago.

    I’ve been taking saunas 3x a week for close to 30 years now (all via an inside feed). I don’t have an oxygen meter, but if I did (and someone should do this), I would put money on the fact that both an electric stove and an outside feed wood stove contribute to a hot room with LESS oxygen than an inside feed. Why? draw. Wood stoves draw oxygen in order to burn.

    When we build our saunas, we install venting – intake venting via a generous crack along our hot room door. As wood burns it draws in fresh air, creating a current of fresh air. Electric stoves and outside feed will draft only via the principle of “hot air rises.” So, there you have something to think about, albeit counterintuitive. And I’d be happy to wrestle this concept to the ground further with your neighbor as I prescribe not to be an expert but an interested student who also appreciates fresh air in my sauna sessions.

    PS.. With that same oxygen meter we could see what happens when we toss water on the rocks. Steam is just liquid H2O… that’s 2 parts Oxygen and I gotta think that action should crank the oxygen meter higher, as we lean back on the bench and “aaaaahhhhh” take in the steam.

  32. glenn touches on the key point: ventilation. if the hot room was super-tight with no intentional ventilation, then inside feed would not work very well and the neighbor would be correct. but you don’t want the hot room super-tight, regardless if electric, wood, natural gas, whatever.

    my parents in northern wisconsin heat their home exclusively with wood stoves. the house was built in 1980 and insulation/sealing knowledge back then wasn’t what it is today and the house was ‘leaky’ enough that combustion air supply wasn’t an issue. they put in all new windows/doors a couple years ago, with much better insulation/sealing around the frames. they were having issues with their stoves due to the house being so tight. they actually had to add an outside air vent to bring in fresh air so the stoves would work.

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