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A tutorial on optimal operation of a Kuuma wood fired sauna stove

A few words about the Kuuma stove.

This stove is our best friend.  This sauna stove is 400 lbs., and has been designed and refined over 3 generations of Lamppa sauna builders.  The Kuuma stove burns super efficiently. Because of the efficient burn, when the stove is tuned properly, we need to use less wood than with other sauna stoves, while producing maximum heat.

Lighting the Kuuma Stove.

It is important that the firebox if free from ash.  Use the ash rake to pull all ash to the front and down the air chambers into ash pan below.

Empty the ash pan.  Ash can smolder for hours, sometimes days, so be extra careful when disposing ash.  Dispose ash in a non combustible receptacle vs. a standard garbage can.

Start a fire.  

Keep Ash pan door open.  Pull damper lever (middle lever) all the way up.  This allows for maximum oxygen within the firebox.

A crumpled up piece of newspaper and a handful of dry kindling is all that is needed to get a fire going.  2-3 sticks of firewood may be added once a good fire is going.

UPDATE: Alternatively, many are having huge success with the “upside down fire technique” more information here.

Once the fire is roaring, after about 10 minutes or so, add a couple more sticks of dry, seasoned firewood.  Lay firewood in parallel, along the base of the firebox on top of existing wood and coals. Unlike a campfire, the Kuuma stove is designed to allow for plenty of air flow surrounding the wood.

Tending to the fire.

About 20 minutes after ignition, the firebox should be very active and all wood should be well ignited.  At this time, close the ash pan door, keeping the damper in the up/open position.

After about 45 minutes from ignition, the sauna hot room should be about 130-140f.  As the stove heats and the fire becomes hungry for more wood, use the ash rake to pull hot coals from the back of the fire box to the front, then lay on a stick or two of firewood, again in parallel and on top of the coals.  Pulling coals forward is a very important procedure. As the Kuuma stove burns from front to back, bringing coals to the front enhances the burn rate and efficiency (Kuuma means “hot” in Finnish!).

Maintaining hot room temperature.

Once the sauna hot room is up to desired temperature, begin “tuning” the stove by lowering the damper to about ¾.  This reduces air flow and burn rate, but counterintuitively produces more heat. 70% of the heat in a stick of firewood is from the gasses from combustion.  We capture this energy by turning smoke into flame. A well tuned Kuuma produces “the dancing blue flame.” A mature fire with damper at ¾ to ½ open produces the most heat while consuming the least amount of wood, keeping the heat within the hot room vs. going up the chimney.

Also, one can tend to a Kuuma sauna from the outside, just by observing the chimney.  A clean burn means zero smoke is being emitted from the chimney. We are looking to achieve no smoke and only heat trails emitting from the chimney.  The Kuuma should burn smoke free starting about about 10 minutes after ignition and throughout the entire sauna session. Seeing smoke means the fire needs tending.  More oxygen and pulling coals forward are the two primary solutions to a smokey fire.

If a fire has been neglected and only a few coals are left in the firebox, we can perform “sauna stove CPR” and resurrect matters by pulling any remaining coals forward, adding a few sticks of firewood as detailed above, and opening ash pan for a few minutes.  This will reignite and re energize the fire. This is the only time when we should consider ash pan being open during a sauna session.

Towards the end of a sauna session.

One more sauna round?  Should we add one more log?  Pull the coals forward, then decide if you need another log.  Chances are you may not need another log. The mature hot coals provide a lot of heat, and more immediate heat.  By pulling the coals forward, the Kuuma stove produces very little ash. Many sauna veterans need not have to empty their Kuuma ash pans but once every few sauna sessions.

In addition to seeing the sauna stove fire, sauna veterans become tuned to listening to their sauna stoves.  With a well tended fire, as we pull coals forward and toss on another log, we will notice the stove responding with a “tck, tck, tck.”  This is the sound of expanding metal from our sauna stoves as it reacts to increasing heat in the fire box.

Looking for a great instruction manual on stove operation?  Having guests over to use your sauna?  Looking to AirBnB your place?  This one pager is a fantastic piece to print, laminate, and post outside your sauna. (Thanks John!)  Click here and print:

Sauna Instructions as pdf.

Sauna Instructions as Word file.

There is a lot to take in with burning wood in our sauna stoves.  Some of us get really into the process of wood heat and tending to our sauna stoves.

For More On This Topic, Check Out This Interview with Daryl Lamppa


Daryl Lamppa on Sauna Talk

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16 thoughts on “A tutorial on optimal operation of a Kuuma wood fired sauna stove”

  1. Glenn,

    I was planning on lining my 6×8 sauna with cedar T&G but I recently came across a good deal on some clear cedar plywood. Do you know anyone who has used this material for the interior of the sauna? My concern is that there is a possibility to de-laminate. Any advice would be great!

    Thanks,
    Kory

  2. i’m with you Kory. You nailed it (cough). De-laminate is a concern, despite what the mfr. may say about the strength of the glue. T&G is the proven winner.

  3. Glenn,
    If all goes to plan I should be rolling my new small Kumma into my hot room next week. When looking at the instructions pdf I noticed that they refer to the flu damper. In your photos that I have seen I don’t recall seeing a damper on your stoves. Up to now I was not planning on installing one either but now I am curious as to whether or not I should….. Pros/Cons? Does it make much of a difference?

  4. Glenn,
    The picture you show of stove here, how old is this stove? Looks all rusty. Wonder if it’s a bad paint job or what? Looking to purchase one, but if after few years of use it looks like that, than I want to stay away from it. Please let us know, thanks.

  5. In your build plans, it doesn’t y’all much about position/angle of stove. What do you recommend? My assumption is the stove door would be perpendicular to the hot room door, allowing for the door to open to feed the fire. Is that correct?

  6. David:

    Yes, in the ebook, we don’t get too detailed about stove position/angle and setbacks as these depend upon the stove mfr. requirements. That said, you’re spot on with your description. More times than not, as you detail, the sauna position is best that the stove door opens perpendicular to the hot room door. The open area just inside the hot room is dual function. It allows for the coming and going, as well as proper clearance and access to the stove for loading.

  7. Hey Glenn,

    Sorry if you’ve already covered this elsewhere. I am looking for the dimensions of a small kuuma with heat shields and water tank. Basically, what are the dimensions of the footprint and the stove’s pipe exit in reference to them? Obviously, nothing will be as precise as making a template off the stove when it actually arrives, but having a good idea of the footprint would be really useful for starting the build. I’ve seen the dimensions of the stove by itself, but nothing about the size of the shields or the water tank, or how far forward from the back of the stove the chimney vents. Thanks for any help!

  8. Hi Glenn,
    We’re going to (finally) hook up our small Kuuma stove this weekend. I thought I had seen an article at some point about how to cure it, but can’t find anything on your site or the stove site. What’s the best way to break in the stove?

    Thanks!
    Kari

  9. Hi Kari:

    Seasoning a new Kuuma: We like to do an “outside burn” before install. For this, you can set the ash grate in place and get a fire going in the fire box. Typically, I won’t add the fire brick at this time. Then over the course of a couple hours, add wood and get a bigger and bigger fire going.

    Couple other things:
    stove window: the yucky paint fumes will collect on the window. This is a bummer as it’s super hard to clean. That said, I’ve had good luck burning off the ash on the window with an ever increasing hot fire. I have also “cured” the Kuuma with the door open. I’ve set fire brick in front of the door opening to help encourage a hot fire. You can try a combination of this.
    stove pipe: It’s a good idea to cure with the stove pipe in place, outside. This will “cure” the stove pipe also, and you’ll get a hotter burn.
    ash pan: closed (of course, or the wrath of Daryl will be upon you).

  10. I live in northern Nevada and don’t have a lot of choices of wood to gather and burn in my sauna, we do have a lot of juniper around but not sure if it is a good choice.
    I am a contractor, therefore I have a lot of scrap Doug fir 2×4 and am using it but seems to burn real quick.
    Any pros and cons on either species would be appreciated

  11. Hi Wade:

    I’ve burned whatever I’ve had access to for decades. Sure Birch and some ash or oak blend is the best, but the Kuuma stove has a damper, so when burning 2×4’s you’ll be able to damper down, restricting oxygen, and it’ll provide a slower, cleaner burn vs the *poof* hot and fast action from construction lumber.

    I had a great winter a few years ago, working my way through 2 SUV loads worth of 2x8s that my buddy was getting rid of. They were moving from their warehouse, and the 2x8s had been used for pallet racking. Hadn’t seen the light of day in over 40 years. I had such a good time with that wood. All cut to length and ready to rock, efficiently cubed in my garage.

    Fire up the Kuuma and bam! Mega BTU action and round one in 20 mins.

  12. Hi!
    We are building a wet sauna and are researching a wood fired stove. The hot room is 8 feet wide by 7 feet deep. We are looking for a stove that is not 400 lbs,! Also, we want steel construction so it will last awhile. Any recommendations? Thanks!

  13. Well, I’ve taken about every sauna in every sauna stove available, and I stand by the 400 lb. stove..,

    Hope this helps, Nora!

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