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Your Guide to Venting a Sauna

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Good Venting Actually Makes Your Sauna Hotter

It makes sense to think that you want to keep your sauna hot room tight, with a minimal gap along the bottom of the hot room door and very well sealed walls. And this is partially true. We want to contain heat. We want the heat to resonate in the hot room with good, dense lämpömassa (think heavy stone wood fired pizza oven vs lame ass thin metal toaster oven).

But with venting, I’ll be the first guy to admit that I used to build my saunas tight, trying to contain heat within the hot room with minimal air gaps. Then I went back to Finland. In Finland, the pros call for about a 10-15cm gap along the hot room door. You crazy? I was always thinking of a gap for a mouse, tops. But 10-15 cm? My cat can fit under that door gap. These generous gaps along the hot room door work only if the room adjacent to your hot room is ambient. A gap along the hot room door does not work, for example, in saunas where you exit the hot room to the outdoors.

And what about wall vents? It makes complete sense to install them and have chutes for opening and closing, but truth be told, I wouldn’t open the wall vents much. My thinking was, to really crank the heat, shouldn’t we keep the wall vents closed? No, no, no. Once again, as with many things in life, the opposite is true, and the Finns are right. (Insert political argument about education, health care, public transportation and/or salmon soup here).

How is it That a Well Vented Sauna Can Feel Hotter Than a Poorly Vented Sauna?

Any idea? Need a clue? Ok, try this: ever stood outside on a frozen lake on a sub zero calm day? Not so bad, is it? Now, compare: ever stood outside on a frozen lake on a sub zero windy day? You don’t last too long, do you? “The wind blows right through you, it’s no place for the old.” – Fairytale from New York, The Pogues. Wind chill will kick our ass.

Follow This Principle With Sauna

A well ventilated sauna creates air flow (circulating good heat). Instead of wind chill, a well ventilated sauna creates a hard to notice yet gentle breeze of heat. You won’t necessarily feel it, but a well ventilated sauna will feel hotter than a poorly ventilated sauna as warm air is passing over our bodies on the sauna bench. A very subtle yet slightly hot… breeze.

You can probably sit in a poorly ventilated sauna for a longer time than a well ventilated sauna. What’s worse is that in a bad sauna, you will leave the hot room wiped out, exhausted because you’ve been breathing stale, poorly oxygenated air.

Yes, it is Counterintuitive

Good venting actually makes our sauna feel hotter. And good venting helps keep our saunas fresh and smelling clean. When we apply the Bake and Breathe method, along with good venting, our saunas don’t seem to be needing to be cleaned much, if at all.

What is The Best Venting System for Your Sauna Building?

12/28/2020

Creating the best venting system for your sauna building is critical. We are happy to visit with a professional builder who is finely tuned to air circulation and proper venting. Enter Bob:

From the Desk of Bob Daigle, Casco Maine

We’ve recently completed the construction of our outdoor / stand alone Sauna. In the process of thanking Glenn for his book & insights, he asked me to explain a bit about our construction technique. In particular, what the air circulation strategy we used.

Full disclosure, we built our own home a few years ago. I have worked professionally as a builder / carpenter, so I went into this with a “build a very tight small house” mindset. Our own home is ICF construction and is incredibly tight. This saves us on heating, but also has serious ventilation consequences. To address this in our home we use a whole house ERV to swap indoor air with outdoor air, replacing the air in our home roughly 8x per day. We monitor our indoor house environment with a Netatmo device (highly recommended). This device measures humidity, temperature, noise, and C02.

Bob's well vented authentic wood burning sauna

Given this experience, from the start of this sauna project, we were thinking quite a lot about air flow & ventilation. This would be a small building with one extremely tight room (Sauna Room) and one adjoining room with less need for “tightness” (Changing Room). The Sauna room changes temperature radically. Further, it introduces large volumes of moisture into the entire building envelope. To me, this combination spelled potential problems, unless proper ventilation was built into the design.

Bob's hot room, with optimal ventilation

Our solution: Build the Structure Using the Same Ventilation Techniques We’ve Used on Houses

The first step was to insulate the walls & ceilings using a proper moisture barrier. In the Sauna room we used batt insulation between the 2×4 studs, foam sealed the windows. We used the Reflectix vapor barrier on walls & ceiling (taped), as Glenn suggested in his book. We also insulated the Changing Room walls. The exterior plywood sheathing was covered in standard exterior house wrap. The entire structure’s interior & exterior was then covered with T&G Northern White Cedar (Maine grown!).

Bob's sauna loft, showing ridge vent for good ventilation

The Best Venting System Consists of a Few Parts

First, the door leading into the Sauna from the Changing Room has a 1/2” gap at the bottom. The sides & top of the door are sealed using a foam strip in the door casement. The gap at the bottom of the door allows the influx of fresh air, particularly when the stove is operating. This has the benefit of supplying oxygen for the fire. Also, the air gap keeps the floor rather cool & dry, as the air washes over during its’ travel to the stove. (I really notice and appreciate this cool draft as I’m kneeling in front of the stove, mid-sauna, to add more wood).

Secondly we used the same strategy as we did on our own home. The roof was built to provide a 12” overhang on all four sides of our 8×12 structure. A 12″ overhang not only looks pleasing, but it also provides a place to install two 12” soffit vents in both the front & back side eaves. These are simple / cheap metal one’s from the Home Depot. In addition, we installed a Ridge Vent on the ridge of the roof. Again, the ridge vent was simple to install and is inexpensive.

Finally, instead of putting a ceiling on the changing room, we left it open. An open ceiling allows the cool down room to fully participate in the movement of air supplied by the soffit vents & ridge vents. This provides a “cathedral ceiling” effect in the changing room, and also gives direct access to the wood stove chimney pipe going up through the attic. This access to the attic chimney helped a lot in the chimney installation. Also, the open ceiling is easy to inspect. I was thinking about adding a vent on each Gable end, but decided against this as overkill. The combination of the soffit vents & ridge vents are sufficient.

looking up at Bob's changing room cathedral ceiling for good air circulation

The Result Seems to be Working Quite Well

The stove clearly has a strong supply of air coming from under the door. I suspect the stove gains much of its air volume from the soffit & ridge vents when it is really cranking & requiring oxygen. Also, I feel comfortable that any moisture that makes its way out of the Sauna Room is being dispersed through the vents.

By the way, we are using the “Bake & Breathe” technique Glenn has recommended. We leave the Sauna Room door closed for the night while the Sauna Room is still quite hot. Then we open the hot room door in the morning. We are finding the Sauna Room bone dry in the AM. Then we just crack open the Sauna Room door and let the entire structure breathe until the next Sauna session.

One final point, due to our (my) focus, maybe an obsession?, on indoor air quality / circulation – we’ve installed a Carbon Monoxide alarm in the Sauna Room. We find it reassuring that the feeling of deep relaxation is coming from the heat & steam – not from some bad gas vapor.

Again, a big Thank You to Glenn for his guidance. I stumbled upon his website when thinking about building this Sauna and it has made an enormous positive difference in our ability to do this right. Merry Christmas – looking forward to the Maine Winter!

Step by Step Directions for Installing Sauna Vents

  1. Locate your vent location. I like a vent about ear level when sitting on the upper bench.
  2. Find and mark your studs. Be sure to be clear of studs and safely between joist cavities.
  3. Make sure there’s no wires. Let’s not drill into where there’s any wiring.
  4. Use hole saw to drill through sauna paneling.
  5. Continue drilling into exterior sheathing and paneling until center drill goes through to the outside.
  6. Pull out and go outside to find the hole saw drill hole.
  7. Drill out the outside with hole saw, creating a clear channel from the hot room to outside.
  8. Dry fit 4″ Hinged Louvered Vent Hood.
  9. Cut back metal duct length on vent hood so that it is flush to paneling, or recessed 1/8″ ish.
  10. Silicone the back of the louvre vent and install from the outside.
  11. Install vent cover chute. Two screws or 3-4 finish nails should do it.

A Better Way to Vent Your Sauna

1/3/2009

A better way to vent your sauna is to allow for about a 1/2″ or so crack along the bottom of your sauna door.

Why is this a good idea?

  1. No extra engineering of having to put an air intake vent in one of your walls.
  2. Air coming in through a crack in the bottom of your door will help keep your floor dry, the incoming air acts as a gentle blow dryer, running along the floor to feed air your sauna.

What Do We Do if Our Saunas are Poorly Ventilated?

Two things we can do:

  1. Let’s pop in a couple wall vents. Borrow or dig out a simple hole saw and drill out a couple holes. Set in dryer vents and flash around the inside with chutes. The mobile sauna shown here illustrates wall vents..
  2. Let’s make a wider gap along our hot room door. Unpin your hot room door, lay it on saw horses, and cut off a couple inches along the bottom with a skill saw.

Is it Time for Mechanical Ventilation in Our Sauna Cool Down Rooms?

How many hours have you spent enjoying yourself chilling out between sauna rounds in your cool down room? For many of us, if we were to put a pencil to it, I think the number could be greater than many other things in our lives. Could anything be better than our time spent cooling down? For many of us, the cool down is as important as the heat up. A good cool down space is valued and important for equalizing our body temperature and enjoying the benefits from the rubber band theory without jackrabbiting our sauna rounds.

In English, the cool down room is also often called the changing room or poorly translated from German: the antechamber. With saunas built along masculine lines, this room may also be referred to as the man cave, dog house, or party room.

Cool Down Room Climate Control

For many, we are able to “infinitely control” the temperature in our cool down rooms by simply cracking open the door to the outside and / or cracking open the door to our hot rooms. Yet this action, generally, only controls our cool down room temperatures. Humidity, on the other hand, tends to linger. Especially when it’s very cold outside. On cold sauna nights, we can see a massive amount of steam leaving our cool down rooms, but as our cool down room temperature goes down, moisture collects on surfaces (glass, metal, towels, beer cans). Many love the climate of cool and moisture. It’s akin to a hike in a rainforest. Magical. However, excessive, lingering moisture is not great for our sauna buildings.

Back to Mechanical Ventilation

Is your sauna cool down room begging for mechanical ventilation? If yes, where is the best place to locate a cool down room vent? Up high makes some sense, as bathroom mechanical vents are on the ceiling, but as warm air cools, it releases moisture as water. Maybe a mechanical vent is best lower on the wall in the cool down room?

From the Mailbag

8/12/2010

A SaunaTimes reader asks: “Do I have to vent (exhaust) the opposite side from the heater? I am thinking about having a small gap on the bottom of the door (intake) and then having a vent on the upper end of the door for exhaust. Something tells me that this is not a robust design. Oh yeah, my door and heater will be on the same side of the sauna. Door will be centered and the heater will be in the corner.”

I say: Good move on venting with a crack along the bottom of the door. It’s easy and functional. As far as an exhaust vent, the first thing to note is that an exhaust vent is really only to allow stale air to escape the sauna, say, after a sauna session. Some purists like to vent during a sauna, but if you are using wood heat, there is enough fresh air pull just by wood combustion.

But an exhaust vent is a good idea. You build a sauna once, so may as well put one in. Your instincts are correct. Put your vent on the opposite wall to your door, and I like about a foot from the ceiling. They’re easy to install. Drill or jig saw a 3 1/2″ hole in your wall sheeting. You can buy a vent with the exterior grill already in. Screw it to a stud and insulate around it. When you do your t&g cedar, just cut around the round metal pipe. I like to make a little vent control slot thingy using some t&g cedar, with a little wooden handle.

PS. If you have already built a sauna without an exhaust vent, no worries, just open the door when you’re done.

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88 Comments

88 thoughts on “Your Guide to Venting a Sauna”

  1. I am building my sauna in an old greenhouse. I am currently trying to choose a location for the Saunacore 5kw heater. I just noticed from installation instructions, I need an intake vent. Does the intake vent absolutely have to be located underneath the heater? Thanks John

  2. John: Intake vent for a wood burning stove: I like a slat along the bottom of the hot room door. This allows for cool air to be brought in along the hot room floor, usually along a cedar slat floor which makes it cozy and nice to stand on. This acts as a gentle blow dryer, helping your wood slat floor dry. THE BIG SELL: This tip and more are detailed in my Build your Own Sauna ebook. $20, and will save you mountains more in money saving tips.

    Also, please take some pics and share your build. A sauna in an old greenhouse seems like a sunny, bright idea!

  3. So then do you recommend not putting an intake hole just below the heater?
    My heater will be just to the right of my door on a perpendicular wall.

  4. Erik: Instead of the bother of an intake vent, as you make your custom hot room sauna door, leave a crack along the bottom of the door such that as your sauna stove pulls air for combustion, it will draw air from changing room, along floor, to the stove. BONUS: this naturally occurring process acts as a gentle blow dryer for your hot room floor, slowly drying your cedar duck board floor as life rolls along. Sometimes physics works in our favor. All this is detailed in my ebook, and happy to assist.

  5. Lance:

    Glad you are enjoying saunatimes. As to your venting situation, just put in your vents wherever you can. I like venting from hot room directly to outisde. But, it’s not a big deal if you want to put a vent in your interior wall to changing room. But also, put in another vent in your changing room wall to the outside.

    Use the chutes as detailed above. I really like that you can have vents in multiple spots and just control them how it best suits your hot room. Every sauna has its own soul (ask you Finnish wife about that) and good venting helps the soul come alive.

  6. hey Glen, I’m building my sauna as I write this. My wife is Finnish and I’ve fallen in love with the sauna… my question is about venting…

    My stove was originally going to be on an outside wall, but if I put it there I wouldn’t be able to have 1 full bench on one wall… my stove is home made with a water tank off the side with a water jacket… can I put it on an interior wall, and keep the original vent on the outside wall? It would be about 1.5 feet from the stove… or should I vent into the changing room? I haven’t cut a hole yet so I can move vent location if needed…

    Thanks,

    I love your website!

    Lance

  7. Claudia:

    Spot on. Storing wood in the hot room is not recommended. It’s like storing potato chips in the hot room, with the bag open.

    That said, it’s common to keep a few logs along the floor in the hot room for the spontaneous sauna stoker in you. Especially in Winter, where losing the rock paper scissors contest on the bench, to see who has to go get a log, is that much more of a drag.

    Now, more than what you asked, in this Sauna Talk episode with Daryl Lamppa, a foremost expert on wood burning by a country mile, he commands that wood should be room temperature for best burn. Which makes sense, as we don’t want to be tossing in icebergs into our sauna fire box. So, truth be told, in Winter, I store about 1-2 saunas worth of wood in my hot room, and cycle it in from my outdoor wood pile, down low. Then, with the bake and breathe method, it does pretty well in there staying dry for when it’s sauna stoking time.

    Hope this helps!

  8. Hi Glenn,
    I have a question not related to ventilation but to wood storage. I came across this cute picture on pinterest (see https://www.dwell.com/collection/bath-and-spa-aba71657/6122818467279704064 ) which shows a wood sauna with a wood heater and tons of wood piled next to the bench. I’m wondering if this is actually recommended. Won’t the wood turn too humid to keep using it? It’s just for the purpose of the picture, right? Thank you, Claudia

  9. Hi , I need some help.
    Last year we found a cheap sauna heater on Kijiji and picked it up , we have since converted an old shed into a sauna and are looking at hooking it up.

    we realized that we would need to wire it but it seems all the electricians around have no idea how to wire it.
    we have the heater and a little panel that was given to us and a sticker on the heater giving us information.

    “A genuine home spa product” ( seems its a company no longer around from the 80’s
    model HE-75 ( cant find anything online)
    serial# 15360
    Volt: 230
    Amps: 32.6
    Watts: 7500
    Phase: 1

    what kind of thermometer do we need to be able to run this thing? it has 2 bigger black wires and one smaller white wire.

    Thank you for any replies it would really help us.

  10. Hi Brooks, glad you love the site and that my book is helping you.

    As to your questions, yes, and yes, and yes! tarpaper is just fine. beveled cedar siding is the bomb. and yes about the vents. Any way you go, above is a really easy and constructive way to vent your hot room. And you’ll get bonus points for making and installing chutes for open/close user friendly ability.

  11. Hi Glen,

    Love your site and the online book. I am in the process of converting an old 6 x8 shed in the backyard to a sauna.
    The only problem with the shed is it has no sheathing . Just a tarpaper wrap and some nice beveled cedar siding. Will that still work or should I re-sheath and re-side. ( I live in Washington State.) Also for venting can I use those little circular metal vent disks that they install after blowing in insulation. Thanks,Brooks

  12. brooks, got a buddy in seattle who has an outdoor unit with tarpaper (roofing felt) and cedar exterior, been a rager for years. as for venting, those metal discs ‘work’ but venting is all about square inches of free air space. you’ll need several of those little discs to get an effective total surface area for free air movement.

  13. Glenn, love the site and have your e-book. Building the sauna this summer and doing a lot of reading on your site.

    Venting question. For best results would you want flow in=flow out (door vent sq/inch to equal wall vent sq/inch)? Or is it more a preference thing?

  14. Mike.. .im sure there’s some science to it, but I install vents by feel. Every room is a bit different, yet the general feel is a generous crack along bottom of hot room door and a couple vents up high, say a foot from the ceiling, opposite wall of door. And these vents have chutes, like in the photo above. Chutes are closed during heat up, and we open them at will when we sauna.

    3x air exchange and the pros in Finland will approve.

    And if anyone wants to wrestle a better vent design than this, i’m all up for it. I’ve vented every which way from Tuesday, and the above system, I like.

  15. Hi Glenn,

    A construction/ventilation question for you…

    Should the back of the cedar panels be touching the foil vapour barrier or separated by an air gap?

    I’d read somewhere else about fixing battens over the barrier first and then panelling to the battens so that the wood can dry out more easily from both sides and any condensation drip down the Vapour barrier rather than Soak into the wood

    Any advice about this and if the same goes for panelling Walls and ceiling?

    Much appreciated
    Alex

  16. Hi Alex:

    Yes, you can do battens to separate your wood paneling from vapour barrier. Yet true be told, I have never bothered with this. It makes our hot room that much smaller, and it creates a gap that in my opinion is best not to be there. I have saunas built over 25 years ago that are looking mighty fine. I think moist cedar is miles better than moist vapour barrier, trapped in the dark in some cavity. That’s my thinkin’

  17. Hello,
    I recently sent a message and one comment in your reply was to use the 16 foot wall of my 8 by 16 foot sauna area for the wall were it would be best to place a the door. I was interested in exactly why that was. I was not planning on this wall For a few reasons but I could adjust my plans. Thank you, Daran

  18. Hi Daran:

    Yes, all things being equal, it’s nice to run the door from the changing room to the outside on an adjacent wall. Reason for this is flow.

    As we exit the hot room, and make a turn for the outside door, we leave the cool down room fairly intact.

    Running the changing room door on opposite wall to the hot room door can turn our changing room into a pass through room. A train car effect.

    All this was told to me by a few different architects (not one, not two, but a few) and so I started building my saunas with door to outside along the adjacent wall, and have always appreciated this design element.

    And for bonus, designing the sauna building with a reverse gable to the long wall, we start to incorporate a deck space with overhang, that 3rd space, not which the Starbucks guy talks about for their hanging out in the coffee shops, but the 3rd space so wonderful for sauna – where we can hang out on the deck or garden all misty wet with rain, after a cold plunge or cold shower, and really expand the vibe.

    Anyhow, these are subjective considerations, but I throw them in the mix for you as you are in the planning stage, and no begrudging to anyone who has build their saunas differently, as the best saunas are ones that get fired up and appreciated (vs. remain on a piece of drafting paper and never happen).

  19. To be clear.. are you suggesting vent under the heater on the wall AND vent under the door of 4″ or just a 4″ door gap at the bottom?

  20. Hi Dave:

    Vent along the low side of your hot room AND a gap along the bottom of your hot room door.

    GETTING NERDY: What we’re looking for is good air flow. When one opens and closes the hot room door, we don’t want any air pressure differential. Good air flow from drain, low vent, bottom of door allows our saunas to breathe and for wood stoves get the air they need for proper combustion.

  21. Thanks Glenn! I’m doing an indoor/electric sauna(8KW). So I think I’ll just do a 3×10 vent under the sauna heater, 1″ door bottom gap, and 3×10 exhaust venting. The Drain is hooked up to the indoor plumbing so I get no play there too much. However that’s double and then some what the Manufacture recommends for the venting. Jealous of the extra heat the wood stoves make and give, but this article made me feel comfortable giving my sauna double the recommendations of the Electrical heater manufacture recommendations. Thanks again!

  22. Dave: You got it. This may be getting weird, but as “every sauna has its own soul”, one of the ways our saunas speak to us is through venting.

    Good venting allows us to connect with the soul of our saunas.

    I see venting as an art, as much as a science.

    eg. I was in my buddies horse trailer sauna yesterday, and we were geeking out on venting ideas and options for his unique/custom build. What’s notable here is that it was all field verification.

    We each asked silently, kindly, and respectfully what our sauna wanted to help breathe, and after tossing water on the rocks of his sauna stove (the heart), and letting the silence allow us to connect to the soul of his sauna, the sauna spoke back to us.

    With a 4″ hole saw, and knowing where studs are, vents can be added easily later, after we’ve gotten to know our saunas.

    https://www.saunatimes.com/sauna-culture/sauna-philosophy/does-your-sauna-have-a-soul/

  23. Dave: The beauty of “every sauna has its own soul” is that we can help make it friendly and inviting. 🙂 (insert plug for DIY ethos here).

  24. Very interesting. I feel like calling “bad sauna” it is too colorful, for instance, some ppl may like to stay longer, and the author admit that “cat size” gap under door will change it. Personally, never ever in my life experienced a bad sauna, rather different character of her. Remember my first sauna… real one, with buddies and beer, in Saki, Krym, Ukraine. I met love of my life the evening, obviously it was one of best saunas!

  25. I am wanting to build a Sauna in an attic space that is amazing. We have a large area that is 22ft by 8 or 9 ft. Facing the area we plan to install has the slanted ceiling on the left side. At the back side their is a Chimney. The other side we plan to add a bath room. That is where i am stuck. Would love to send some pics for ideas. Also, venting is what i am concerned about as well.

  26. What if your sauna doesn’t have a changing room? I’m afraid such a wide vent on the sauna door might allow vermin to get in. Would a vent by the heater and another up near the ceiling be sufficient with the sauna door sealed tight?

  27. Jay:

    Yes, the wide vent along the hot room door is a Finnish export, as pretty much every sauna in Finland has a pre room or changing room.

    So, for your case, what I would do is, no vent along hot room door, but install a dryer vent a few inches off the floor. And I like the “gentle blowdryer” effect, having the vent in location so as to allow for air flow along your floor to feed your stove.

  28. Hi Mike, Bob here – – I did not put any additional ventilation ports in the Sauna Room other than the 1/2″ gap under the door. Originally I was planning to do so, but after reading Glenn’s book and his comments about ventilation, I decided to follow his guidance. My “fallback” if needed was to just crack one of the windows we have in our Sauna Room – but to date I’ve found this is not necessary. I agree with him that the gap under the door provides plenty of oxygen for the stove. And, the occasional opening / closing of the Sauna Room door provides fresh air into the Sauna Room. In our sauna the draft in the chimney is excellent, good evidence it is getting plenty of oxygen. Hope this helps…

  29. Hi Greg:

    Others with more thermal dynamical experience may be able to explain it better, but stone is an excellent conductor of heat, which sounds like good news but it’s not. Stone sucks heat out of a sauna like Dementors sucking out the soul in Harry Potter.

    So, I’d not be thinking about building a sauna up against a brick wall, unless you created a thermal break to the brick. (rigid insulation).

    Stone and heavy brick work in commercial Banyas and big saunas because of two main reasons:
    1. The masonry is isolated. Once heated, the heat is retained within the material (this is when stone being a good conductor of heat is a good thing).
    2. Commercial saunas and banyas are heated almost 24/7. So a massive amount of lämpömassa is a desired/good thing.

  30. Hi All,

    Love the website and I’m super keen on building my own sauna this year. I’ve got a spot in mind on our back patio but i have a quick question before I go to the next stage of design. Is it possible to build the sauna up against an external brick wall? So one of the sides is built against the external wall with potentially a sloping roof to the other side?

    Thanks,

    Greg.

  31. Bob, sometime can you stick your Netatmo in your sauna in a seating position (so that its CO2 sensor is at about the same height as someone’s mouth), heat it up to 48-50°c (upper limit for Netatmo to accurately measure CO2), then have one or two people take a warm sauna round or three. It’d be interesting to see what the levels are.

  32. Hi Greg,

    I starting my Sauna build in Aspen Co. I’m planning on an electric heater. The sauna will be 5x7x6.5tall. 166 cubic feet 4.7 cubic meters. I have found a unit called Huum from Estonia. Would a 4.5 kw be the right size for this sauna? The only place I can find this unit is on EBay so I can’t talk with anyone about it.

  33. yes. I saw your drawing. (Crappy red pen was just fine!).

    2×2 firing strips, 16″ on center. glue and screw into the brick (sparingly is fine). Then rigid foam between the joist cavities. Then foil. Then fir that out or just t&g over that. The Sauna Twins are also in the UK and they can steer you towards a free range organic version of poly-iso (Finn Foam), which is a thermal break vapor barrier material.

  34. Greg, IIRC a masonry wall eats up about 2kw per 10 square feet. That’s a lot. Unlike the rocks in a sauna stove that radiate their heat out in to the sauna, a wall like that will radiate a lot of the heat to other than inside the sauna. It will act as a thermal bridge to pull heat from your sauna. There is also a question of what’s on the other side of that and what affect 100°c of heat against it will have.
    As Glenn recommended, you need a break between your sauna and that wall and you also need to be cautious about handling moisture.

    Dennis, the general rule of thumb is 1kw / m3 so you’d likely be OK. I’ve not heard of Huum though, why that? Estonia does have some good sauna.

  35. Hi Glen,

    Thanks for the info. The reason I ask about putting it up against a brick wall is more due to space issue than anything else. I have a narrow run of patio against a small external side wall to the side of the house. so if I can butt one side of the sauna up against this wall this will give me a space of around 2.5 meters wide by 2.7 meters long. So if I understand correctly, I can build up against the wall if i build that side in the same way as the other walls (insulated etc.)

    The max height of the external wall is around 2.7 meters, so I’m thinking if I can build up against this wall i could also use this to build a flat pitched roof to the other end of the sauna.

    I’ve uploaded a couple of pictures of the proposed area below (please excuse the crappy red pen). This is sort of what I’m proposing with the door on the left hand side.

    Let me know what you guys think.

    Thanks,

    Greg (from the U.K)

    https://ibb.co/2Z7Psjd
    https://ibb.co/mJwnsvW

  36. Hi Glenn,

    I’m planning a backyard sauna build this summer and in spite of all that is good, I’ve decided to go electric. I’m a big fan of Bob’s design above (beautiful sauna, Bob!), especially the vaulted ceiling (I’m 6’7 so the ceiling height for me is may bueno). I’m wondering what adjustments would be made in Bob’s design if the stove was swapped out for an electric one. There should be no need for a gap under the sauna door in this case, should there be? Anything else I should consider? Also, at my height, what would you recommend for hot room height? I’m worried 7′ might be a little tight but I don’t want to lose efficiency if I don’t have to.

    Lastly, I’ve looked at the Kuuma stoves and am strongly considering one. That said, I’m having some trouble identifying 2 or 3 electric options that are high quality and great for loyly. Wondering if you can recommend any options that you feel confident in?

    Thanks for all the great content, including your book which I purchased and am cruising through. Looking forward to some time on the bench hopefully next winter.

    Scott

  37. Hi, Bob here.

    Subject – Sauna Room Co2 Measurement using our Netatmo Device.

    This note is to respond to Walkers request to put our Netatmo measurement device in our sauna to measure C02 (Carbon Dioxide). This will give us a good idea of the quality of the air / and ventilation inside the Sauna Room. I did this today – the results were quite interesting.

    First, a bit of background on Co2. Co2 is Carbon Dioxide, NOT Carbon Monoxide. Carbon Dioxide is an important “marker” for air quality, plus in high concentrations makes you stupid (er) & groggy. Carbon Monoxide, (I’m not talking about his here), can kill you.

    Carbon Dioxide, Co2, is produced by several things – the burning of fossil fuels at the top of the list. But also, it is caused by people breathing. We humans emit Carbon Dioxide every day with every breath we exhale. In a tightly closed room (like a sauna, or a tightly built house), a group of people can bring Co2 to very high levels, very quickly. Good ventilation is the key to resolving this.

    In our home we use an air measurement device (Netatmo) to measure a bunch of things – temperature, humidity, noise level, barometric pressure, and most importantly – Co2. The reason for this is our house is super tight – and even though we have an ERV constantly circulating the air – it is amazing how quickly the Co2 can go up – either by cooking without putting the hood fan on, or having a large group of people in the house, or both if the chef starts drinking the cooking wine.

    For reference, average outside Co2 is roughly 400 ppm the world over. This, by the way, has climbed significantly from pre-industrial revolution levels. But, 400 ppm is still OK for us to breathe – “clean outside air”. Inside our home, we typically see 450 – 500ppm over the course of the day, going up a bit when we cook dinner.

    As an aside, Co2 at 400ppm the world over is not so good for our planet… but I digress…

    When we start seeing 1,200ppm or higher in our home, it’s usually because we burned something on the stove, or have a few people over. When we see Co2 over 1,200-1,500ppm we just crack a window for a while to bring it back down.

    With Walkers request in mind (good one by the way), I put our Netatmo device in our Sauna and measured the result.

    The results – with two of us in the Sauna & Netatmo at “nose height”:

    – Round 1: At 150 degrees we had a Co2 level of 1,325ppm at end of round. This round was appx. 20 minutes; we took a break for 10 minutes.

    – Round 2: The sauna temp had climbed to 160 degrees. At end of round 2 (20 minutes), we had a Co2 level of 1,652ppm. At this point I took the Netatmo out of the sauna – it was getting too hot for the Netatmo device to work properly.

    – Round 3: 180 degrees for 20 minutes. No measurement, but I expect Co2 likely a bit higher. The air felt, smelled – and seemed just fine.

    My conclusion is this – – I think our ventilation strategy is working fine. The draw on the stove is strong. The air feels clean, not stuffy. The Co2 is climbing during our rounds, which I expected for such a small tight space – but not to a dangerous level. However, when we have more than the two of us in the Sauna I will crack a window to introduce a bit more air ventilation – – not imperative, but I think sensible.

    Thanks to Walker for asking this question – – it really shined a light on the actual air quality in our wood fired sauna.

  38. Hi Bob, thanks for doing that. Great info. Your and my sauna seem very similar (assuming yours is about 8 m3?).

    For comparison, a sauna of 2 cubic meters per person, 6 air changes per hour (based on fresh air supply rate (CFM)) and good air distribution & mixing (E.G., a good Finnish sauna) with bathers spending 15 minutes in and 15 minutes out for 3 rounds calculates to CO2 levels of very roughly 582, 594 and 606 ppm. I say very roughly because I don’t know what the mix rate would be. I assume it is very high but we need a lot more tests to know for sure. Given my experience in Finnish saunas this seems about right.

    My own sauna w/ just me so 12 m3 per person results in 633, 721 and 842 or w/ 6 people (2 m3 / person) calculates to about 1798, 2326 and 3052. I’ve currently got about 9 CFM or 1.2 changes per hour which largely agrees w/ my calculations above. So far so good.

    More: https://bamasotan.us/2020/12/sauna-ventilation/

  39. Hi Glenn,

    Thanks so much for this initial information. I’m 100% building the sauna in the next 3 months or so. I’m just going to lay out my new decking area then concentrate on this bigger project. I’m going to download and read your book. Sure I’ll be back in the not so distant future with some more advice!

    all the best,

    Greg.

  40. I’m writing this with a confession of sorts – – maybe a “learned experience confess”. My opinions & strategy on ventilation have changed…

    I am, by the way, the person who wrote the original Guest Blog Post above – all of 3 weeks ago. As before, I am still & surely a Sauna neophyte – but endeavoring to keep learning all the time…

    My post on Sauna ventilation / construction was fun to write and I’ve really enjoyed reading the responses – particularly Walker’s, who seems to be a mix between a sauna enthusiast and nuclear scientist – impressive. His request to measure the Co2 really got me thinking. As you may have read, when we measured the inside air, the Co2 climbed pretty substantially the one time I measured it with my Netatmo device. Not to dangerous levels, but enough to get my attention.

    Then, I read an earlier blog post from Glenn’s site, which talked about how Finnish Saunas have a 4” gap under the Sauna room door – vs. the 1/2’ gap I had in ours. Also, Glenn’s comment that he took dozens of saunas on a trip to Finland, with no feeling of dizziness / fatigue. Then, the real kicker, was a quote from the Finnish Sauna Society thru a link Walker sent me in one of his blog post reply’s – (Bamasotan – https://bamasotan.us/2020/12/sauna-ventilation/). I found this article, by the way, an excellent discussion of sauna ventilation and the negative impacts of excessive Co2.

    Here’s the quote:

    U.S. Saunas Are Not Sauna.

    What most people in North America experience is not sauna but a warm room with bad air.

    “90% of saunas in North America are bad. The other 10% are worse.”
    – Board Members, Finnish Sauna Society

    – Mikkel Aaland

    This quote really hit me, a bit of an insult – but also some serious experience based wisdom. The reason behind this commentary is, of course, insufficient ventilation in the Sauna Room.

    So, with all of 3 weeks of Sauna experience, a burgeoning non-expert who is rapidly becoming an addict – – I went into change mode. I cut off the bottom of the Sauna Room door to allow a 4” Gap, and when using the Sauna I opened the window inside the Sauna room (across from the stove & in front of & to the side of the upper bench) roughly 4″ – 6” (it’s a casement window and slides side to side). This is the window you can see on the front of the building in my photos.

    By the way, depending upon the wind & pressure outside the building, I’ve found that “tuning” the window opening is required. Sometimes open 6”, sometimes 3” – but always open when we are using the Sauna.

    With this increased ventilation strategy the difference in the Sauna experience was, in a word, dramatic. In our very first Sauna Session, with window open 6″ & 4″ door gap:

    1. I could feel, with my hand, a fair amount of very hot air moving out of the window. Yet, despite this, the temperature in the Sauna actually climbed! We had hotter temperature inside the Sauna than ever before, reaching nearly 200f on round 3! Despite managing the fire in the wood stove similarly, it seemed it was burning hotter? The chimney draw, as before, was excellent, but I suspect it was just getting more substantial and purer oxygen to fuel the combustion. In subsequent sauna sessions, we have reduced the amount of wood we put into the stove a bit to manage the temperature to about 170-180f.

    2. The difference in the air “feel” while sitting on the top bench was a game changer. Really, a game changer. My wife Maggie put it best – – it reminded her of snorkeling / scuba diving. Her metaphor: Before, she was having a good time, but her mask was fogged, obscuring her vision substantially. After these changes, the mask cleared and she could see dramatically better, no more foggy goggles, plenty of pretty fish. Indeed, when sitting in our Sauna now, the air just seems to have more clarity.

    3. I totally concur with her assessment. It’s hard to put a finger right on it – especially given our lack of experience – – but it just feels so much more fresher, and the heat feels purer / hotter.

    My sense is that we have improved our Sauna experience substantially by increasing the ventilation. I do understand every Sauna is different, but ours is a pretty standard configuration in an 8′ x 12′ building – (88″H x 88″L x 88″W). And, at least for our Sauna, we’ve discovered that increasing the ventilation does not negatively effect the temperature, in fact the opposite.

    So, if I were to re-write the article on Sauna Ventilation – – it would be quite different. I’d stick with our overall building design – ridge vent, soffit vents, cathedral ceiling in changing room. But, my advice would be to go overboard with the ventilation in the Sauna room, whether it is with door gaps, windows, vents – – keep it “tunable” so you can dial it up or down. And, have some confidence with heat – – even with all this fresh air zooming around, it still stays plenty hot in this super-well insulated small room.

    As I learn about this wonderful subject & lifestyle, I’m convinced good ventilation is perhaps the most important ingredient to having a positive and enduring experience.

  41. Spot on Larry. As you know, every sauna as its own soul. The stove is the heart of your sauna. Ventilation is its lungs. Happy to hear that yours is breathing well.

  42. My name is Larry Bounds from southern Utah at 6,000 ft.

    I built a 6’x10’ Sauna on an existing wooden deck with 3/8” gaps between boards,
    And a 1” under door gap and a Vent inside the sauna room at ceiling height that can be adjusted for air flow, this works quiet well,
    I tiled the floor and two walls for my wood stove heat barrier
    And the air flow in through the floor and out the vent is amazing,
    The steam level is lacking for my liking with the ceiling vent wide open, so we adjust as necessary for a meaningful sauna experience,

  43. I love this post and the comments!! I just wrapped up my exterior and installed my chimney from from ceiling through roof. I’m so pumped!!!!!!!!!!!!

  44. Bob. It looks like your sauna door opens in. Am I seeing that right. From all my research having the door open outward for safety purposes seems to to be the standard.

  45. Hi, I live in on small homestead here in Norway. I am planning to build a bath room with shower and sauna in the basement of the existing house. The distance from concrete floor to wooden ceiling is 190 centimeters. Is this sufficient to build a sauna? I am planning to use a Tylo electric oven for heat. I have made some drawings and estimate that 20 centimeters will go away to sauna ceiling, and 20 centimeters to sauna floor. So that means the actual sauna room will be only 150 centimeters from floor to ceiling. Is this ok and sufficient? Is your book for this type of sauna or only for separate sauna house with wood stove?

  46. Peder:
    Every Norwegian I’ve every known has been tall and thin, like a string bean. No wonder you guys kick ass in cross country skiing! (built for speed).

    If you’re building up your ceiling and floor 40 cm total, leaving you with 150 cm, per my calculations, that’s 5′ (60″) about the height of an Italian, like Danny DeVito, so non benne, my opinion.

    What I would be thinking of doing is firing out your ceiling and floor with 2×2 pressure treated lumber, 16″ on center (or cm equivalent) glued and screwed to your stone/cement, and fill the joist cavities with rigid insulation.Then over that, apply rigid poly-iso, or similar, with foil vapor barrier attached and then panel. Maybe with a bit of an air gap. This configuration would be about 3″, or no more than 8 cm. and give you a good thermal envelope to kick into gear.

    My ebook is mainly geared to backyard free standing saunas, but there’s a lot in there, like drain, window concepts, door building, etc. etc. If you purchase the book and it doesn’t work out, shoot me an email, I’ll come visit you in Norway and pay you back (I so want to get over there again! hashtag: corona travel deprived).

  47. My sauna dimensions are approximately 7 1/2′ wide x 7′ deep x 7′ high. The door is on the same wall as the stove but is about 3′ from the stove. I can heat the sauna to temperature in about 30 minutes even at -25C outside.

    I have a wood fired sauna stove and followed your recommendation of leaving a 1 1/2 gap under the door. What I have found is that the air flows in to the sauna via this gap from the ante room and just makes the floor cold on it’s way to the stove. The air stratifies near the ceiling and requires a towel to be swung or waved to mix the hot and cold air.

    I am considering putting in an air supply pipe behind the stove heat shield from the outside wall to make the ante room air more of a neutral pressure. The pipe would be 4″ in diameter to match the flue diameter. Any thoughts or suggestions?

  48. Jeff,

    You’re on the right track. I’d be thinking about two vents from outside to hot room. One down low, the other up high on opposite wall. Each with chutes. Infinite, optimal control.

  49. Informative article Bob! A well-ventilated sauna is essential for making the experience more comfortable and relaxing. The original Finnish saunas were pits dug into the ground in which a fire was created to heat stones. Steam was generated by throwing water over the stones, to increase the temperature in the pit.

  50. Are a few smaller knots ok on the bench planks? How big is too big for a knot on a cedar bench? What do you think about drilling out the knot and using some filler?

  51. Hi Daran:

    A few smaller knots are totally ok on sauna bench planks. It’s those gnarly ones starting at about penny size that start to become a pain in the ass.

    Good thinking on the drilling out knots on bench planks and replacing with filler. But I’m wondering if the filler compound may be just as “ouch” as the knots themselves. Sort of reminds me of a one step forward, one step back dance towards the same place we started from. Maybe. Send me a note and pic if you go this route.

  52. Ok thanks Glenn, I will for sure do an experiment it’s worth a try. How hot should I turn up the Oven to make it comparable with a small scrap? DARAN

  53. This is all so helpful. Thank you, Glenn. Your website continues to provide very useful information. We installed our intake air vent below our sauna heater but on the other side of the wall is a shower and we’re worried about having a vent by a shower. It’s a 4″x10″ rough opening. The outtake is located on the opposite corner up high (also 4″x10″ with a closable register cover.) I’m more inclined after reading this to delete the 4″x10″ intake under the heater and just add a nice sized gap under the door. 2-3″ below the 24″ door is 48-72 square inches of fresh air intake (even more than the 40 square inches from the original vent idea.) If you think this is doable, I’m going this direction!

    Thanks again,
    Liz

  54. Liz:

    Glad Saunatimes is helping you.

    Now, with venting, I can get very woo woo. Every sauna has its own soul. It’s up to us to listen to the soul of our sauna, very quietly and consciously, and understand where and how it wants to breathe.

    No rules, no snarky jibber jabber from know-it-alls on Facebook, no ventilation schematics from sauna companies.

    Some tools to help you listen and feel: A candle. Move it around your hot room. Watch where the flame wants to go. Silence and solitude, to help you connect more to your friend, your sauna. A libation of choice, to help you relax and lose yourself and be present on the bench.

    You are a sauna builder, and you’ve created a soulmate. Your health and wellness retreat.

    In this moment, Liz, I am sure you will know how your sauna wants to breathe.

    I know you can do it. 🙂

    I know you can do it.

  55. Hi Danny:

    You’re welcome. It’s great to share sauna insights, especially for appreciative folks in another hemisphere. (Global outreach program).

    1. Stove on the outside of the building.
    Well, we have to think about what we’re trying to do. Are we heating air or heating mass? If the stove is on the outside of the hot room, how will we heat rocks to create steam? Please search lämpömassa above this page, and you can read more. And you mention that you’d like to put the door of the stove to the outside, and keep the stove, mainly inside the hot room. And this is good, and this is done with positive results.

    2. Stone walls.
    As a default recommendation, we add firing strips, glued and screwed to cement, then rigid insulation on the inside of stone walls between the joist cavities. We try to get a “thermal envelope” in the hot room. As stone is a good conductor of heat, and that sucks for sauna. So we want to isolate that.

  56. Hello

    I am currently building a sauna in India.
    I have a laterite stone structure with a concrete slab roof as the basis of the building.

    I was considering to make a hole in the stone wall so that the door to the stove would be on the outside of building, taking up less space inside and ensuring the stove has a great oxygen supply. I will use a Himalaya Rocket Stove for this purpose as finding a specific sauna stove in India is difficult and this specific stove has a design that would work very well in this way.

    What do you think about having the opening to the stove of the outside of the sauna. The climate here is generally warm so being outside to refuel the fire is not at all an issue. We do not need a changing room here as the outside temperature, especially at night is perfect in that regards.

    Before insulating the structure and adding the wood, I could install the stove and do some tests with smoke to better understand the movement of air in the room in regards to where the air would go after entering under the door or from other places.

    thank you for this great resource.

    Danny

  57. Hello

    Thanks for the response.
    Yes, just to clarify, the stove will be on the inside of the Sauna. Only the door will be accessed from the outside of the sauna. As the walls are brick I don’t see any risk to having the heat of the stove so close to the walls. The space-saving I was referring to was in regards to needing to leave space to open and close the door and load the fire when the door is on the inside.

    I will now frame the stone wall and insulate it with Rockwool and thermal bubble wrap, both of which I have managed to source here in India. Do you see a difference between using Rockwool with a backing such as kraft paper or aluminium foil if there will anyway be an additional vapour barrier added over the top?

    thanks again!

  58. the principles to follow are:
    1. no double vapor barrier (to avoid moisture trapping)
    2. in stone environments where “sweating” of walls is a realistic scenario, no batting but use rigid. think of Rockwool as a Scottish herdsmen caught out in the rain. His sheep and his sweater need to dry out eventually.

  59. Hello there!

    Thanks for this.
    That makes total sense in regards to the double vapour barrier.

    Can you explain more about the ‘sweating ‘ of the walls that you described?
    And to clarify, you are saying to use a product called rigid instead of the Rockwool? I thought that the vapour barrier would stop any moisture from getting into the Rockwool?
    Is there a specific type of rigid insulation that I should search for?

    thanks so much for the help!

    Danny

  60. Great article Glenn.
    We are building a sauna and we plan to have it well ventilated as suggested. The firebox will be fed from outside the heat room so there will be a limited amount of air exchange due to draft. Were going cut off the bottom of the heat room door as suggested.

    My question is where did you get those lights? Those are exactly what we are looking for.

  61. Hi Glenn,

    We’re in the process of building a small, rustic sauna and have got to the stage where we’re sizing the door and thinking about vents, and I’m not sure how to proceed. We don’t have 2-level seating, just a bench with our feet at ground level. The sauna is an outdoor sauna, with no changing room, just a hot room with a door to the outside. If we have a 2″ (or similar) gap at the base of the door, won’t our feet freeze? We’re in Nova Scotia Canada so it will get cold! I want to get the venting right but I don’t want to create any bad drafts that make it uncomfortable. How do the Finns deal with basic one room outdoor sauna venting? Thanks!

  62. Izzy,

    In all my travels around Finland, I’ve never seen a one room outdoor sauna. All have pre-rooms or often called cool down rooms or changing rooms. You will have to do what you can. If you search “ventilation” on this website, you will get more illustrations of vents. I recommend vents with “chutes” so you can open and close. You can close during heat up., and open most of the time in operation.

  63. Hello Glenn
    I’m planning on building an outside sauna roughly 9ft x 6ft on a purpose built deck in Australia.
    The deck will have small gaps between the deck boards as per a normal deck. If I build without flooring, will the gaps serve as adequate incoming ventilation that the article mentions if I put vents in?
    Also the joists of the deck are pressure treated pine (the newer non arsenic kind), should I be concerned about that at all?
    What do you think?
    Thanks
    MJ

  64. Hi MJ:

    1. Deck with small gaps. For sure. Assuming that you have air flow underneath, like a standard purpose built deck, you will have plenty of air flow, and no lower vent needed.

    2. Pressure treated pine. Well, if this were my sauna, I probably would stain this material or paint it with Kills or something like that, and then, maybe, put a cedar duck board atop. This may be overkill but to me this would be a good compromise. I’m sure there are folks who would never have treated lumber in a sauna, but if these are the same folks that don’t drive automobiles or drink beverages out of plastic, well, then they sure have a point. But this treated material is way down low, and sealing it or covering it up to a good degree would give me peace. That’s just my thought. Good sauna MJ!

  65. Hello,

    I am currently building a lean-to style shed, 12×12 in dimensions. 4×12 will be used as a storage shed with a segregated door for access. the remaining 12×8 will be used for a 6×8 hot room and a 6×8 changing room. I will leave the cathedral ceiling in the changing room but want to install a level 8 foot ceiling in the hot room. My question is in regards to if you have any mold/mildew concerns for the insulated cavity above the level hot room ceiling and the roof rafters of the shed? If so, what are the best recommendations to address this concern? I will have a roughly 20″ overhang on all four sides of the structure so I could investigate venting that way with an additional vent on the roof. Any recommendations would be extremely helpful!

    Thanks.

    Sam

  66. Yes Sam! Ridge vent is a great option, as would be gable vents above the hot room.

    The cavity above the hot room is the trouble spot, as you identify. The above should cycle air on its own, but installing a mechanical bathroom style vent, and letting it run for 20 mins or so after final round will really help pull the moist air out of your sauna building. And of course, the bake and breathe method for the hot room will bring you further along, as well.

  67. Hi! I’m in Northern MN and have the same issue as the Nova Scotia fellow above. Single room, small barrel sauna, and cool feet! I was thinking of installing a small electric fan somewhere in the barrel to get the warm air to flow all around. Is that a viable option, even though it’s definitely non-authentic? I do have vents, but when I open them I can see the cold air dribbling in.

  68. Hi Glen,

    We like your website!

    We built our sauna with Tylo heater a year ago. When the heater tries to reach the temperature above 184 F, it turns off and we have to wait 20 min to reset it. Our sauna has one in vent under the heater and one out vent in the corner across the heater under ceiling. Vent’s diameter is 4 inch.
    Do you have any ideas or suggestions how to fix this problem?
    Thank you in advance.
    Alex.

  69. Alex,

    You can try messing around with the location of your sensor in your hot room. Forgive, as I am just now getting electric sauna heater training, so i’m still a little inexperienced with good troubleshooting at this time.

  70. Hi Glen,

    Your website has been very helpful and I have thoroughly enjoyed many of your podcasts – thank you!

    I am about to embark on my first sauna build. I have done a lot of research and believe I have a good idea of what needs to be accomplished. I will be using an electric heater, since it is going in the basement of my home.

    The dimensions that I am working with are: H 85″ x L 85″ x W 66″. I believe the following bench heights may work best, however I am open to any and all suggestions. *Note I am dropping the ceiling from 96″ to 85″.

    44” ceiling to top bench.
    17” from top bench low bench.
    18” from low bench to raised floor.
    6” raised removable cedar floor on top of tiled flooring.

    The one area where I have found it hard to gather information is regarding mechanical ventilation. I want this sauna to be as close to perfect as possible. Do you have any recommendations on what fans (brand/model) I should look into?

  71. Josh:

    It’s super crazy timing you are emailing me with this question. I just got back from Finland from a “ventilation quest.” I can’t recommend anything specific today, but I will have very specific, proven suggestions for you tomorrow.

    One thought. Your build will probably have the sauna heater adjacent to a common wall (vs. an outside wall). I suggest (in DIY spirit) that you install what you think to be a simple, basic bathroom fan. Odds are that this will be just fine for sauna adaptation purposes. If it fucks up or isn’t the right way to roll, we can switch out this fan and reinstall a more suitable piece of hardware.

    I am hugely interested in this. Please email me your process. And let’s take pics. This work you are doing is part of the more ambitious project that Saunatimes is spearheading “taking back sauna in USA” and one of the slices of the authentic sauna pie is good ventilation (and shame on the bullshit industry for not making it clear.. or understanding it themselves).

    Sorry, i’m on a rampage.. but when you experience the disconnect between sauna in Finland, and sauna in US and A… well.. you can’t help but get Borat like about it. (and i’m not even talking about light bulbs being called “sauna”).

  72. For the guy above with the barrel sauna. Yes I use a 6ich usb fan to circulate the hot air down to your feet. In my barrel I bought 2”x 6” redwood and raised up one bench. This puts your legs online with the stones and easy to put your feet up on the bench across the way.

  73. Thanks Glenn. I’ll be sure to take some pictures.

    I found what seems to be a great fan. Super quiet, water resistant, and is good in heat up to 284F. The fan is made by Noctua and the model is (NF-F12 iPPC-2000 PWM, Heavy Duty Cooling Fan, 4-Pin, 2000 RPM (120mm, Black). I’m going to install an intake fan above the heater and an exhaust fan below the upper bench. I’ll probably install a vent without a fan underneath the heater and one on the opposite wall just below the ceiling. This way I’ll be sure that I’ve gone completely overboard :-). I might even put a gap under the door, so that I have zero lingering questions about if the ventilation could be better.

  74. @Josh, that’s crazy that you just posted this today because I am nearly complete framing in a sauna room and have been wondering about a similar install. My sauna space is in such a space that I can only do 1 extra-wide L-shaped bench because of sloped ceilings that I can’t change. Heck, I’m lucky my significant other let me commandeer the space she did for this sauna. You can sit pretty comfortably under the sloped ceiling on a low bench and lie down comfortably, but a 2nd bench is out of the question.

    So in my case temperature stratification is absolutely what I DON’T want. I was planning on lowering my ceilings to about 6′ 6″ since no one would be benefitting from the top 6 inches anyway, and putting a mechanical vent ABOVE the heater and the exhaust under the benches to stop the temperature bulb from turning off the heater prematurely (https://researchgate.net/figure/Mechanical-ventilation-is-recommended-for-indoor-saunas-The-vent-for-incoming-fresh-air_fig1_12163683#:~:text=Mechanical%20ventilation%20is%20recommended%20for%20indoor%20saunas.%20The,on%20the%20opposite%20wall%20under%20the%20sauna%20benches).

    This doesn’t seem to be a very popular installation model, but to me it makes logical sense that, especially in a small space, it would take an unnecessarily long time to heat up a sauna to temperature if the temperature bulb is constantly touching 195F well before the lower levels of the sauna have heated up. It seems like mechanical ventilation ABOVE the heater would help to prevent the issue. Could even be an energy savings because the energy to run a small fan is much less than the energy required to produce wasted sauna heat over an extended heat-up time…

  75. As an addendum, I would think that you would want the opening inside the sauna to have its louvres directing the air UP and along the wall and ceiling, as opposed to just letting the ventilation fan blow air into the middle of the room. Pushing cold air along the ceiling is the optimal design for forced air HVAC cooling, so I would think the same principle applies here. Basically we’re trying to cool off the air near the temperature bulb to keep the heater running and the air mixing until the ENTIRE room is at the set temperature, and not just the upper level.

  76. Hi @Greg, I’m still researching and planning the build. I’ll probably start in the next couple of weeks. I’ve literally watched every sauna build on YouTube and have read all the comments. I’ve taken notes of the suggestions and mistakes that people have pointed out. I’ve also gone through this website with a fine tooth comb. There’s tons of great info on here.

    I didn’t think about deflecting the air up along the wall to the ceiling, but it makes sense. I was more focused on bringing fresh air into the room and removing CO2. I’m use to gym saunas that have zero ventilation. When 4 or 5 guys are in there it doesn’t take long before you start to feel dizzy and lightheaded. It ruins the sauna session.

    Would you be able to use the extra 6 inches if instead of dropping the ceiling, you raised the bench and installed a 6” raised floor? This way you’re above the heater/rocks as much as possible.

    Also, I’m not sure I understand the logic behind installing the thermostat right above the heater, as suggested in most of the owners manual’s. This makes no sense to me as it’s not a true indication of the average temperature in the sauna. It would make more sense to have the thermostat sensor at about head height close to where you’re sitting. This way it’s registering the actual temperature of the space that’s being occupied. This is where I’m going to attempt to install it.

  77. Josh,

    Thanks for taking a few pics. Let’s think about a mechanical vent guest post. It’s timely and relevant. Thanks for sharing this information!

  78. @Josh
    I agree with you on the temperature bulb. As a fire prevention measure, I guess maybe there’s sense in having it at the absolute hottest part of the sauna. Though I have a hard time imagining that you could ever get the room hot enough to combust without some bigger problem like bad wiring or tinder falling onto the heater.

    I’m definitely a believer in the fresh-air-for-fresh-air’s sake logic as well. It just seems like a bit of a twofer to mechanically ventilate the sauna above the heater with an electric unit. The unit can’t run when the power’s out anyway, so the ventilation might as well be mechanical for how little energy it takes to spin a little 25cfm fan. This is the one that I’m going to try: https://www.amazon.com/gp/product/B009OXTWZI/ref=ppx_od_dt_b_asin_title_s00?ie=UTF8&psc=1

    The volume of the sauna is about 220 cfm, so I’m hoping this will ensure an air change every 10 minutes without blowing all of the heat out of the sauna.

    My slope constraint is a bit hard to describe. It’s actually two sloped walls coming together into a corner. One thing I was considering was actually raising the floor so that the entire sauna’s footprint is the “lower bench” to maximize the area where you can spread out, instead of devoting like 40% of the square footage to a walking path. But this would require stooping or scooching to get around to the edges of the room, and I’m not getting much buy-in from my significant other on that idea. The other idea to maximize space is to cheat the 6’2″ minimum clearance for our FLB-60 Harvia heater and put it under one of the slopes. I’ve got a spot next to the door that goes from about 5′ to about 6’4″ over the space where the heater would sit. I’m thinking 1.) That this won’t be a problem in the first place, 2.) That I’m going to be ventilating outside air over the heater so it will be cooler there than it otherwise would be, and 3.) I could put a bit of non-combustible material above the heater. I don’t really like the look of tile in saunas, but if it lets me cheat my height constraints a bit I might buy into it…

  79. Greg, I have been looking at that fan as well. It also seems like a great option. It will be interesting to see if the mechanical ventilation makes a noticeable difference to how enjoyable the overall experience is. As I mentioned, most of the saunas I have been in don’t even have ventilation. I’m hoping it makes a big difference.

    Having the lower bench as the footprint is kind of what I am doing. Instead of all that dead floorspace I am going to build half of the lower bench around the heater, so there is more room to sit/lay. The remaining half of the floorspace will be raised. You’ll be able sit upright with your feet on the floor on that side of the lower bench.

    Will your sauna have a drain? This is the one area that I am still unsure about what I am going to do.

  80. How did these mechanical ventilation experiments turn out? Planning my own outdoor, small sauna using a 5kw electric heater and hoping for good ventilation, circulation and enjoyment. Life in coastal BC Canada gets very grey and bleak in winter. This little house of heat will hopefully change that for our family. Open to any tips and tricks for fresh air and good heat in an electric sauna.

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