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“My wood burning sauna takes 3 hours to heat up:” Problem solved!

light steam graphic

Unless it’s a savusauna, or John’s Wisconsin sauna, a wood burning sauna shouldn’t take 3 hours to heat up. One of the great things about a wood fired sauna stove is that wood heat can pack quite a punch compared with electric heat. This, of course, assumes that you have invested in a kick ass wood burning sauna stove. Tin can toaster ovens exist in both electric and wood fired sauna stove configurations, of course, but we know better than this. We know not to throw money down the drain by purchasing a sauna heater we can carry with one hand.

So, what happens if we have invested in a kick ass wood burning sauna stove and it takes forever to heat up?

Good news: Here comes the four horsemen for high performing wood burning saunas. Let’s discuss them one by one:

  1. Draw
  2. Ventilation
  3. Insulation
  4. Good wood (that’s what she said)

Draw

A wood burning stove of any type requires good draw. Good draw requires a chimney system that is tight. We light a piece of birch bark or a crumpled piece of newspaper within the firebox, and then the hot air pushes its way up the chimney. In its wake, more air is pulled into the firebox to replace the warmer air going up the chimney. As the flame gets brighter and bigger, the draw increases, more draw and faster.

What can impede this process is a leaky chimney system. Like a vacuum with a hole in the hose, a fire can burn in the fire box but there is no air going up the chimney and no air to come behind to fuel the fire. You need a chimney system that is tight.

Imagine putting a plastic bag in the gap where your wood burning sauna stove connects with your stove pipe. Then imagine going on the roof and pouring water into your chimney, at the top. You’d want water to fill up the chamber. No leaking. That is the hypothetical measure of a tight chimney system and the foundation for good draw.

A second issue is too many bends and twists in your chimney. Here our problem is different in that hot air struggles to work its way through bends and horizontal runs to push its way through the chimney. I am a big fan of chimneys that go straight up from the sauna stove through the hot room ceiling and up through the roof. Yes, 45 degree elbows and chimney through the wall can work. But these systems will require more “oomph” in the form of an extra crumpled piece of newspaper or birch bark or perhaps another form of petroleum persuasion.

Good draw up the stove pipe and up the chimney (no leaks in the vacuum hose)

Ventilation

Ventilation in the hot room is not just critical for a great sauna experience (read: the holy trinity of good sauna: heat, steam, ventilation). Ventilation is critical for burning wood in our sauna stoves. Just as a candle will extinguish if you put a glass over it, a fire in a sauna will want to do the same in a poorly vented sauna hot room.

A fire in a wood burning sauna stove needs lots and lots of oxygen! A shit ton more oxygen than you may think it needs. Why? because in addition to oxygen for fire to burn, bodies on the bench also need lots and lots of oxygen. Just as a candle goes out if you put a glass over it, a fire inside a wood fired sauna stove will putter and sputter if you deprive it of oxygen.

As Wim Hof says: “breathe motherfucker” and this is what we want to do inside our wood burning saunas.

Vents with chutes offer infinite control of the action

Insulation

If living in a temperate wimpy ass climate, you can get by with a wimpy insulated sauna. Barrel saunas, as example, separate themselves from the hot room to outside with a layer of wood. That’s it. And if you are taking a sauna in the foothills of Los Angeles or burrows of Sydney, you may get by with a wimpy insulated sauna. But a good sauna is like a green egg grill. In a well insulated hot room, the BTU’s produced from a wood burning sauna stove efficiently and effectively heats the hot room. Heat from the sauna stove transfers into the stones and mass of the material in the hot room. And we get the deep dense reward of good heat.

And foil vapor barrier is a must.

Simply put: A well insulated sauna heats quickly and thoroughly.

a sauna hot room, with blocking for sauna benches, ready for foil vapor barrier.

Good wood

The fourth horseman to a wood burning sauna is good wood (that’s what she said). It’s obvious to those of us who have learned the hard way, but “dead wood” is as bad as “green wood” in terms of not producing the kind of BTU’s to make our saunas hot.

Dead wood is over seasoned wood. Overly dried out, devoid of gasses wood.

Green wood is wet unseasoned wood.

The best wood is about 20% moisture content. As most of the BTU’s in firewood is from the gasses emitted during combustion, not the material itself, we want to ensure we are burning well seasoned, not over seasoned decent firewood. More on firewood here.

Good wood, haircut sold separately.

If you checkmark these four horseman and your sauna still takes forever to heat up, well, then it’s time to turn your attention to your sauna stove. A kick ass sauna stove is your best investment to good sauna. Good heat makes all the difference. We build our saunas one time and get to enjoy them the rest of our lives.

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5 Comments

5 thoughts on ““My wood burning sauna takes 3 hours to heat up:” Problem solved!”

  1. Thanks Glenn for pointing me towards the Kuuma Stove – it’s a marvel – I light it with one match – an hour later, the sauna is above 200 degrees! – (or cooler if we put in less wood, when we want that).
    It takes minutes to clean and set up each day.
    It produces all the loyly We can handle.
    Adjusting the air intake as it burns is minimal and simple as can be.
    Bravo!

  2. I have all of these boxes checked and more. And unfortunately I haven’t been able to get my sauna above 160. Built with 2x6s. Mineral wool insulation. Size is 7x8x8. Medium Kuuma wood burning stove. Good wood. Good draft in the stove. Struggling to figure out the fix.

  3. Chris:

    Wow.. let’s get this fixed. I just returned from a WI road trip and took sauna with my buddy Jeff, he’s got the same stove, and 8×8 hot room only and he’s running consistently north of 200f. He fires up the Kuuma using the upside down method. Burning mainly ash. His prep time to get up to temp is 1 hr., maybe a bit less, which is same for me. When you open and close the hot room door, are you getting any movement of flame in the fire box? This is a sign of needing more ventilation in the hot room.

    You can try keeping the hot room door open for 30-40 minutes, to test the airflow/venting situation.

    Middle lever up all the way until hot room is about 150f. or so. And you can “cheat” by keeping Kuuma ash pan door open for first 15-20 mins, though technically this is not recommended by Lamppa Mfr.

    We want to see the smoke going clear after about 10 minutes of firing up the stove, and this is best achieved with the upside down fire technique. These are areas of focus.

  4. Chris – I’ve been having similar issues with my sauna we just built last summer. Small Kuuma in an insulated 8x6x7 hot room. Ventilation is the first thing I’m going after – right now the only air coming in is via slated flooring so that’s my bad for not including proper ventilation in my initial design. Actually my biggest mistake was not getting Glenn’s ebook prior to the build! Live and learn. Wondering if I should include an intake down low by the stove in addition to upper bench vents? That would definitely let the stove run hotter I figure – maybe you have similar issues.

  5. Dan,

    A sign that your hot room is too tight is when you open and close the hot room door. Check to see if you see any flame movement from within the firebox. If you do, you need to open things up more. This is where a generous gap along the hot room door can really help. It draws air into the hot room from the cool down room (assuming you have really good ventilation out there) and along the hot room floor. The secondary bonus is that this air movement acts as a gentle blow dryer along your floor.

    Good on you for Sherlock Holmes action.. you’ll get there!.. and yes, most of this and definitely more is within my ebook.

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