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The A, B, C, D’s of venting an electric heated sauna

light steam graphic

*NOTE* This post is not meant to be all knowing, absolute, and it will be updated as we go, and comments below are most encouraged!

The following is based on a 1.5 year empirical study of how air wants to move within an electric heated sauna, and so we’ve come up with A, B, C, D for your consideration.

By empirical study, we mean: “concerned with, or verifiable by observation or experience rather than theory or pure logic.” We did read and note the prior art of ventilation, written within various publications, including the out of print book “Sauna Studies” gifted by Risto Elomma, President of the International Sauna Society. We used these recommendations as baseline for where to point our 4″ hole saw.

Venting: one of the holy trinity of good sauna

Perhaps the best descriptor of what makes for good sauna is attention to the holy trinity. And what’s so funny about heat, steam, and ventilation? If you are like a deer in the headlights trying to figure out good sauna in your life, I want to encourage you to pay attention to these three attributes. And keep in mind that 88% of people who feel claustrophobic, dizzy, or uncomfortable within a sauna most likely feel this way because of lack of good ventilation. The other 12% are like my cat, never adaptable to sauna, and that’s ok.

Heat and steam are subject for their own insights, and there is a lot of great discussion on these two elements of good sauna.

Our two tools for analysis

By studying how air wants to move or not move within an electric heated sauna, we spent hours and hours “rudimentarily messing around.” As example, the entire album of Grateful Dead’s Europe ’72 has been an excellent backdrop for us to light up a stick of incense and chart the movement of air by following the smoke tail.

Also, our second testing device: we started with a cigarette lighter, then graduated to a Catholic Charities wax candle. With this candle, we were able to also watch and chart the air movement within our hot room.

We feel that these two methods for studying air flow within our electric heated saunas provide the best analysis. And after reading below, we encourage you to adopt the same analogue devices for your own air movement analysis.

A lot of sauna variables

As we know, every sauna has its own soul. And how each of our saunas breathe is subject to several nuances. This is why it’s not always easy to follow a prescribed drawing or script. Further, this is why we emphasize the value of a “chute” or slider for every vent you punch in to your sauna. This gives you infinite control and customization of venting and breathing.

In addition, we have reviewed most of the manufacturer instruction manuals. The good news is, like a good brewing recipe for a hazy IPA, the electric sauna heater manufacturer industry is waddling its way towards a consensus on how to optimally vent a sauna hot room.

There are two unique aspects to this proposed ventilation plan:

  1. All four vents shall have sliders or “chutes.” These are adjustable slats that allow for opening and closing each vent. Fully, partially, or open all the way.
  2. The four vents are in spirit to the principle of of “and” not “or.”, meaning that with this plan, we can “optimize” for natural ventilation as well as mechanical ventilation.

The four vents

  • A: Behind the heater, down low. PURPOSE: draws in cool air to help the over limit switch think that things are cool and calm.
  • B: Above the rocks. PURPOSE: draws in cool air to help mix with hot air and steam rising when we toss water on the rocks.
  • C: By you ears, opposite wall of heater. PURPOSE: Interacts with A vent through principle of hot air rising to create air flow. This vent can be criticized for allowing good heat to leave the hot room, yet with a kick ass heater, this may not be the case. And this vent is good for airing out sauna when we’re done.
  • D: Mechanical outbound. Anywhere between 16″ to 20″ from from the floor, opposite wall of heater, with a variable speed mechanical inline (in the wall) fan. PURPOSE: This vent, with the fan switched on, pulls fresh air into the hot room, and pushes air out of the hot room.
electric sauna vents
4 sauna vents for an electric heated sauna that cover all the bases

Working in pairs:

  • B & D vents: The B vent draws in fresh air above the rocks. The D vent has a variable speed mechanical inline fan, pulling air out of the hot room.
  • A & C vents: This is the classic tandem that leverage the “hot air rises” principle. Cool air comes in down low, and exits up high, opposite wall. Saunas heated by wood stoves do well with this method. Instead of vent A, often air intake is via a generous gap along the hot room door. Wood stoves create a draw by sucking wood into the hot room for combustion. This principle creates good air flow, naturally. With electro saunas, we need to enhance the situation.

What we like best

All four have chutes for infinite control. Go sauna, have fun, and figure it out later (incense and or a candle and some good tunes). A few suggested settings to try out include:

  • Au Naturale: A and C vents open. B and D vents closed.
  • Pure Mechanical: A and C vents closed. B and D vents open. Variable speed mechanical inline fan on low speed.
  • Semi schizophrenic hybrid: A open half way. B open half way. C mostly closed. D open. Variable speed mechanical inline vent on low speed.

A set up that has been working well with ambient downtempo playlist on shuffle:

  • Au Natuale epoque : A, B, C, D vents 25% open. Variable speed mechanical inline fan turned on 5 minutes before sauna session, then shut off for quietude during sauna rounds.

Let’s remember: unless stamping out “off the shelf” backyard kits or standard flat packs, every sauna is different. Different atmospheric conditions as air flows differently in different houses or if outside, as Neil Young sings: “cold wind whipping down the alley..”

More songs about..

1. Can your post more clearly define which fan you have had success with?

I have installed this one. I’m open to other’s suggestions as this is a very basic one.

This fan can go within the wall. cut the plug,and hard wire to a dimmer switch.
Muffin fan: a quiet computer fan. Variable speed (note comment section below).

2. Can you explain the specifics of how an inline fan would be installed? Is the fan inside the wall cavity?  If so, what does it plug into?

Yes. What we do is cut the plug in and hard wire it to a switch with dimmer. The vent fits into the wall cavity, inside a 4″ opening. A guy can cut the 4″ opening with a hole saw.

422 hole saw zoom

3. Do you ever put electrical outlets on the inside of hot rooms down low towards the floor? (to power the fan and/or a rechargeable bluetooth speaker).

I try to never put any outlets inside the hot room. It’s best to hard wire directly into lights, like under bench LED and overhead sconce, and run that romex into an outliet outside the hot room. And dimmer switches allow for infinite action.

On the road with David Hanna:

Adding onto that, I think noting that the D vent would benefit from being a mechanical outlet could be helpful–particularly for those building smaller saunas who can’t build as high of a ceiling. 

Last but not least, some of the things that could be beneficial from taking this approach is that it caters to both those who want to optimize their experience and those who just want to build it and not think too hard about it. It solves problems like getting enough oxygen in the room, distributing heat more evenly, and ensuring the sauna can dry out without becoming a petri dish! I think some people who would particularly benefit from this design would be those who are planning to not have a drain and/or people who are limited to a 7-7.5 foot ceiling.

I really liked what you had to say about testing the air circulation with a stick of incense, and I think that would be a great way for people to sort of “dial in” their ventilation scheme by adjusting each chute. 

Do you find yourself chasing the dragon for perfect ventilation?

Instead of chasing the dragon of the perfect sauna, at some point, it’s best to pull the trigger and give ourselves some freedom. We want to be happy with our lives and time in our saunas. It’s good to not second guess everything either by reading too much or having too many options, settings, dials. Just the ones that make sense to mess around with. Instead of paralysis, it feels great to clear our minds and just throw some water on the rocks in peace.

Like a kick ass sauna sound system with a subwoofer and an equalizer, this venting plan will give you a clear head to tune the air flow mix how best for you.

Equalizer itunes

The real experience vs. sequestered with online experiences.

This is sauna therapy, one on on individual therapy. Psychodynamic unconscious feelings can show up in other ways. But not on our sauna bench.

A point where you Authoritarian and never satisfied. Celebrate the joy, let’s not suck out the joy. Mechanical or natural.. or a bit of both.

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18 thoughts on “The A, B, C, D’s of venting an electric heated sauna”

  1. Greetings from Australia.

    I am always interested in the articles about ventilation with how it can totally change the feel of the sauna so this one caught my eye. I have a couple of points to add for consideration from my own experience. I was one of the 88% and often felt dizzy in the commercial sauna I previously used and realised that this was due to lack of fresh air.

    Firstly, we have our electric heater near the door of the sauna with a gap at the bottom of the door and this is out ventilation inlet – and the door opens to the outside air rather than a changing room. I have played around with partially blocking the gap to direct the fresh air more towards the heater which seems to work quite well and the rising air from the heater draws lots of fresh air in. The under door gap can cause some conjecture with what size the gap should be and the lack of control you have once the gap is there – but it certainly allows lots of fresh air to enter the sauna.

    For the exhaust vent, I have it set up similar to the “D” vent in your diagram although the height of my vent is above the lower bench but still below the top bench. I created a chimney in the wall frame where the exhaust air is able to travel up in the wall cavity (without insulation in this section) and vents to the outside air just below the roof level. This cavity chimney creates the suction without the need for a fan as the air is drawn up towards the external vent via a thermodynamic action. I was told that this design is quite common in Finland and went with it and the results for me have been good with no dizziness at all. I haven’t used a smoke trail but will give this a go after reading the article so I can try and see what is actually going on with the air movement.

  2. When I built my electric heated backyard sauna a few years ago, I did exactly this (including using incense!). I ended up with vents A, B, C, and D above plus one I’ll call E just under the top bench opposite the heater. For a fan, I got a 120v ‘muffin’ fan – basically a 4” computer fan with variable speed. It’s very quiet and has so far survived. Usually, if 1-2 people are in the sauna, I use A full open, C quarter open, and E about 3/4 open. Never gets stuffy and has less heat stratification than using C full open and not having E. For bigger crowds or max fresh air, B and D open with fan on and maybe crack C a bit as noted above.

    The best part of experimenting is that the sauna is hot and you can just enjoy the heat after data collection is done!

    As always, thanks for sharing.

  3. Hi Steve:
    Fantastic and thanks sharing your experience with this “art” (vs. total science). Is your muffin fan within D? Have you got a link to where a guy could procure such a device? I think the inline fan I showed in image above is too big of a hammer, and I like where you’re at with your venting action!

  4. Excellent. I think the cavity chimney may be the next wave, as working with how nature intended, vs. mechanics, is always a plus. Kind of ironic for electric heated saunas, but the spirit is there! Anyhow, really great feedback, and thanks for taking the time to chime in here. Clear head thinking!

  5. Hi Glenn-

    This is all very timely and great to see the results of your research for electric sauna ventilation- thank you!

    I had struggled with where to place and how to power/control a fan for vent D, so am experimenting with trying to pull the exhaust air through the changing room. I had installed a Panasonic quiet bathroom fan in the ceiling of the changing room to vent that room anyways, so am placing an adjustable exhaust vent D in the common wall. I’m hoping I can kill two birds with one fan. I figure that if it doesn’t work well for the hot room, worst case, I can close the vent and still have mechanical ventilation for the changing room. I’ll let you know how that works out.

    With all this research I’m wondering- are you still of the mind that the air gap is not a big deal behind western red cedar T&G? I’m about to start installing that over my foil and that question is eating at me a bit. Would sure make it easier for cleating the benches, etc with no gap. Thanks!

  6. I bought the muffin fan off Amazon – AC Infinity brand. I mounted it into the vent opening. At first, I questioned if it would survive – sub freezing temps, high heat, moisture – but it is still going strong. No issues all. I ended up getting a second one to mount into my change room to help remove moisture after a session. No issues with that one either.

  7. Jayme,
    For starters, I didn’t leave an air gap between my foil vapour barrier and my cedar – too much hassle!

    You may find your fan in the cold room and vent between walls works well. Likewise, it may draw too much heat and humidity into the cold room. In my cold, northern climate, too much humidity in the cold room results in a thin layer of ice on the walls and ceiling of the cold room (I shouldn’t have painted the walls and ceiling! I’ll remedy that someday). As noted above, I have a small fan in both my rooms. If I just use the fan in the cold room, it gets very humid in there and that’s just from opening and closing the hot room door and from the small gap under the door. I have to make the hot room fan draw more air than the cold room fan or I have problems. Most of the time, I will use the hot room fan during my sessions, and switch on the cold room fan when I’m done and leave it for about an hour or so to remove excess humidity. Seems to work well.

    Since your fan is much more powerful than mine, I imagine it will be more efficient at removing excess humidity. However, it may also just pull a lot of heat and humidity into the cold room. Time will tell I suppose.

    Good luck on your build and let us know how it goes. Know that putting a hole through an outer wall after the build is done, while nerve-wracking, is really quite easy. You can always mod things after if necessary.

  8. really great intel, Steve. We have had similar issues to what you describe with the 612 Sauna Society mobile sauna. It’s a principle of physics.. warm moist air wants to go to cooler dry air.. that we are itching to overcome, as you well describe.

  9. I found the venting for electric saunas interesting. I have a wood fired sauna and also thought about how to get enough fresh air for occupants and for combustion for the stove.

    I too, placed two 4″ round vents at the locations about head height for each of the tiered benches shown in your diagram. I have slide covers over both to adjust air. The vents are the type used to bring in fresh air on a forced air furnace.

    We have a “chill room” or changing room with our outdoor sauna. I did not want to have air drawn in from the chill room to the hot room under the door since that would mean cold air would have to be drawn into the chill room and that would mean opening the window and causing drafts.

    Our sauna has a 5/8″ treated plywood floor with 1/2 cement board over the top. We have a Kumma wood stove with heat shields on both sides and the back to minimize the distance to the walls that are 1/2 cement board on studs with 1″ steel channels over the cement board and another 1/2″ cement board. (Required to meet UL fire rating.) At the corners of the stove directly under the heat shields I cut a 3″ round hole, so we have four 3″ holes. I have another 1/2″ cement board that is elevated off the floor 1 1/2″ with strips of cement board. The elevated piece just fits between the legs of the stove and extends over the top of the 3″ holes. Air coming up through the holes spreads across the floor while keeping the floor under the stove very cool. I adjust the air flow through the 3″ holes based on the outside temperature. The colder it is the less the opening is required. Remember from science, Pressure1 X Volume1 X Temperature1= Pressure2 X Volume2 X Temperature2. On a cold day, say ten below, and a hot room at 180F and assuming P1=P2 The volume of air coming in below the stove expands big time!

    So far it seems to work. Our sauna has better air than the saunas at the YMCA’s around here but maybe that is because not everyone takes a shower before coming in after a hard workout.

  10. Steve-

    Thanks so much for sharing your experience with the exhaust fan and icing up the cold room. I will probably find out pretty quickly if that is the case and can always come back and cut a hole for another for the hot room as you suggest. Really appreciate the insights!

  11. I have questions regarding the common practice of using forced venting on the “egress” vent rather than the “ingress” vent. Logic tells me we should do the opposite.

    Yes, with a woodfired sauna, the chimney pipe is an egress draft that also pulls air into the sauna through the ingress vents. So perhaps that is why electric saunas try to replicate that effect with an egress fan pulling air out and replacement air in passively through the ingress vents.

    But when you are designing an energy efficient and healthy PassivHaus design, that is NOT the preferred approach. When houses have “negative pressure” inside the envelope, the replacement air can be drawn into the house through the envelope which is NOT healthy. The air can become contaminated and excess moisture can be pulled into the wall cavities through leaks in the envelope.

    In PassivHaus design, the preferred method is slight “positive pressure” inside the house. With controlled ERV driven ventilation with heat recovery. The ingress air is intentionally slightly higher than the egress air flow so that the PassivHaus remains under positive pressure.

    Air pressure will always exit out (or be pulled in) the paths of least resistance. The “positive pressure” in a sauna hot room is principally created by volume expansion of the air with heat, which pushes the excess volume out “any” opening.

    With an electric sauna, there is no powerful chimney draft to bring fresh air in. The positive pressure from air expansion will push out of every vent making them all egress vents if the hot air expansion pressures are high enough. This can result in a lack of replacement fresh air coming in to keep the air oxygenated.

    Logic tells me that trying to combat this problem with the “negative pressure” of an egress mechanical fan will “work” like a chimney draft, but that will cause ingress flow to come in randomly from perhaps less desirable locations.

    Why would we not use an ingress mechanical fan near the stove, designed to blend the fresh, oxygenated air with the hottest air at the rocks of the stove?

    By directing the ingress air with the mechanical fan and letting the egress air passively push out intentionally placed egress vents (due to the positive pressure in the hot room), we would have MUCH better control of air, steam, and heat distribution around the hot room.

    Air egress location is critically important. You want the stale air that collects at the stratification layer (much higher CO2 levels) to push out an egress vent placed at roughly the height of the stones at the far opposite side of the hotroom. What you don’t want is negative pressure from an egress mechanical fan pulling fresh air in at the wrong location and disrupting the convective flows.

    I would posit that airflow would be easier to optimize with a mechanical fan in an ingress vent near the stove, than with an egress fan at any other location in the room. You ALWAYS maintain positive pressure and you don’t risk negative pressure. And you ALWAYS pull in fresh replacement air.

    What am I missing???

  12. As a corollary, whereas it is bad practice to have an egress mechanical fan with a wood fired stove (because it can create negative pressure precluding proper draft and possibly pulling fire box fumes into the hot room), an ingress fan helping to ensure positive pressure and plenty of make-up air will NOT create the same issues.

    An inlet mechanical fan should be capable of being adjusted to keep temperatures moderated with a woodfired stove without causing air quality issues???

  13. Grant Whittle, on the Passivhaus projects I’ve worked on, we’ve aimed for balanced ventilation to eliminate problems associated with exfiltration as well as infiltration.

    The problem with a fan on the supply side in a sauna is that it causes a directed stream of air entering the room, which doesn’t happen with a fan on the exhaust.

  14. Glenn thanks for pointing me to your excellent resources on ABCD’s of ventilation.

    My only question that isn’t obvious to me is whether the mechanically assisted exhaust vent “D” in your example – “P2” in the engineers study – can be plumbed to exhaust straight outdoors like a typical bathroom ceiling fan.

    My planned project in a demised room (former office) in my finished basement, It’s a sauna and adjacent open plan shower and rest area/

    Does “D” mechanically blow into the adjacent shower area or can I plumb to vent right outside with backflow prevention to avoid cold air intake.
    I’d be worried about heat build up in the shower / rest area otherwise.

    Alternatively I could plumb D back through the wall to vent back into the adjacent Exercise Area where supply comes from (similar to Harvias diagram ) and perhaps a ceiling exhaust fan in that space will be needed there to control heat/freshen air etc. Otherwise, would the typical backroom exhaust fan for my shower are, draw enough to make “D” exhaust vent work well passively?

  15. Glenn you’re awesome!
    For those wondering, Glenn provided the following response to me:

    The real winner for D vent is to not make it mechanical but if building an indoor sauna, ideally this vent would be along a common wall to a bathroom.

    Bathrooms can take moisture. And bathrooms have an existing exhaust vent.
    By opening vent D, closing vent C, and closing the bathroom door as we switch on the bathroom mechanical vent, we can piggy bag on the draw of this vent to help air move around and out of our hot room.

    A guy can toggle along with how much to close the bathroom door, to control how much air will be pulled through the D vent.

    In situations where this “piggy back bathroom vent” is not possible, well, in this case we install the variable speed vent in the wall cavity for D and be sure this moist air can get sucked out of our house.

    Sometimes we need to “phone a friend” and engage the HVAC professional. Otherwise we can get ourselves into issues like back drafting and negative pressure in our house.

    For backyard sauna action, well, here we have a lot of freedom. There is a chance that D may not have to be mechanical at all. A guy could mess around with A, B, and a little C and D wide open and the principle of heat rising could have a good chance for convective loop to happen. Where air wants to move on its own.

    And it’s ok to test and feel this. Maybe wire for the mechanical fan for D. But don’t install it unless you need it.

    Spin a towel around. Cue up some Grateful Dead and light up a stick of incense. Become one with your sauna and experience how the air wants to move naturally with A B C D.

  16. A slightly nuanced and related question re venting…
    I’m mechanically venting an indoor electric sauna thru the attic and out the gable end…using an AC Infinity 6″ fan & a combination of 6″ metal & flexible ductwork. The total run is approx 15-20’…fully taped & sealed…w backdraft dampers installed. I live in Michigan & my attic probably gets into the 20-30s periodically in the winter. Do I really need to insulate my sauna venting ductwork to guard against condensation forming on the inside of ductwork? I see no risk of condensation on the outside. The canned answer for hvac seems to be yes, but intuitively it doesn’t seem obvious to me. It seems the ductwork will heat up enough to not condense…and the air movement will evaporate any mild condensation that does form. Any experience or notable comments here from sauna builders? Any input is much appreciated!

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