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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.

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

3 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.

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