Walker’s Notes On Building A Sauna

On the path to building our new sauna we learned that there is a lot of not so good (or downright bad and misleading) information on the web and from U.S. sauna vendors, and that there are a lot of details that are critical to get right and easy to get wrong. We traveled to Finland and Sweden to experience sauna and learn from experts. Like Glenn Auerbach did more recently, we’d noticed a huge difference between saunas in the U.S. and saunas in Europe. Sauna’s in Europe are consistently better. We want to know why.

Disclaimer: I am not an engineer nor doctor. The following is simply a bunch of notes on what we learned building our sauna and that we wish we’d known much sooner. Use at your own risk. I strongly encourage everyone reading this to do further research on all of these topics.

 

Form, Function and Löyly

What follows is about function (and Löyly). It’s about the things that are needed for the best sauna experience- a Finnish (or Swedish or German or …) sauna experience.

Form is important too though and form can enhance function. Sauna is more enjoyable in a sauna that is aesthetically pleasing than one that’s not. Should sauna function ever be compromised for form? Not to me. I’ve had bad sauna and I’ve had good sauna and I’ll take the latter every time no matter how ugly the room. 

Some may be more interested in form and want only what function fits the form they desire. And that’s OK, it just may not be sauna. Saunas Of The World is one of my favorite Instagrams because I love architecture and it has some fabulous looking places, but many or even most of what are on there are either not sauna’s or not good sauna’s.

While I’ve heard a lot of people say that they wished they’d done more for the function of their sauna, particularly ventilation, I’ve rarely heard anyone say (though I have said it myself) that they wish they’d done more for the form.

 

Details Are Important

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

There are reasons for that statement and very good ones. U.S. saunas suffer from a love of don’t-sweat-the-details. U.S. traffic engineers not sweating the details on road design is why we have the most dangerous road system of all developed countries and why a child in the U.S. is 11x as likely to be killed walking or riding a bicycle as a child in Europe. Details are often quite important.

You can tell you’re in a U.S. sauna that hasn’t sweated the details because you get cold feet (they’re actually not cold but quite warm just not nearly as warm as your upper body). Or you have to scrunch up and put your feet on the upper bench (which isn’t good for relaxing, breathing and getting the benefits of löyly). Or you don’t feel a fully enveloping and comforting heat evenly around your entire body front to back and head to toe. Or the sauna simply can’t get hot enough.  

The most critical though is that you have to leave the sauna because you’re feeling out of breath, have brain fog or getting dizzy. These because of too high CO2 from poor ventilation. High blood CO2 also impacts the ability to use sauna for muscle recovery after a workout or from a day of real work as it reduces our body’s ability to deal with lactate. In some cases muscles are even worse after a sauna because of this.

Some things we noticed on our travels in Finland: EVERY sauna required climbing up several steps to the benches from the changing room – feet are nearly always above the stones. EVERY sauna except one had good ventilation. They all had an adjacent shower and with a tiny few exceptions, a window or two. All critical details that make for a much better experience.

The biggest thing we noticed is how much more enjoyable sauna is in Europe. More even enveloping heat front to back and head to toe. No cold feet or chilly backs. And that there’s a huge difference in leaving a sauna having benefited from heat and löyly versus leaving because you feel like you need air to breath. People in U.S. sauna’s who’ve never experienced proper sauna often confuse the latter with the former, we think that feeling of breathing difficulty is normal, but it’s not.

These details are more critical for women. Women are more sensitive to temperature and more uncomfortable with cold feet or chilly backs. More importantly they are, by design, more impacted by high levels of CO2 and so poor ventilation makes for a much more uncomfortable experience for women than for men.

If ten men and ten women experience typical U.S. sauna’s; 5 men will like it and 1 woman will, the rest don’t want to return.  Those same 20 people experiencing proper sauna; 9 men and 9 women enjoy it and can’t wait until the next time. 

A bit of effort up front sweating the details provides thousands of hours of more enjoyable and beneficial sauna for years to come. It’s worth the effort.

Two final points. I’d not say the other 10% are worse but perhaps the other 9%. Around Cokato and Wolf Lake MN are Scandinavian communities …with a lot of good proper sauna’s. Risto Elomaa and others have frequently pointed out to me that not EVERY sauna in Finland and Sweden are done well.

 

7 Laws of Löyly

1 – Your feet are above the stones and the ceiling is just high enough to use a vihta

2 – Ventilation removes airborne impurities and provides consistent pure fresh air for all bathers to breath

3 – Circulation provides consistent even heat around your entire body

4 – At least 8kg / m³ of stones

5 – Sauna can maintain any temp from 80-100°c at bathers head and shoulders and feet are no more than 10-15°c cooler.

6 – You can pour water on the stones

7 – Everyone, men, women and children, enjoys it and feels refreshed afterwards

 

Some Important Details We’ve Learned

So here, some quick notes on what we have learned about sauna design and building (some that we wish we’d learned much sooner). Special thanks to Kimmo Raitio, Jarmo Lehtola, Risto Elomaa, Eero Kilpi, Lassi Liikkanen, Allison Bailes, Glenn Auerbach and many others for their patience in answering my endless questions and their perseverance in making sure that I not only built a proper sauna but understood sauna.

And still learning… Just yesterday, thanks to the folks on the Sauna Design, Construction, Use and Enjoyment group on Facebook, I learned about the importance of an air gap between the foil vapor barrier and the wood walls inside the sauna. This was a mixed blessing because there is almost nothing I enjoy more than learning something new but this one also came with learning something that was missed on our sauna.

Hot Room Space – Minimum of 2 m³ or cubic meters (70 cf) per person plus one (35 cf) for the elf.  Larger is OK, smaller not so much.

Insulation – Insulation of outer walls is quite important. Not so much to be energy efficient but because lack of insulation results in colder walls and chilly backs for bathers. Well insulated walls result provide for better, more even and more comfortable heat on all sides.

Stones Determine Bench and Ceiling Height – Temps are much more consistent, stable and comfortable above the top of the stones than below. Start with setting the foot bench at or above the top of the stones. The sitting bench then is 17-18” above the foot bench and the ceiling 44-48” above the sitting bench. If you have more than two benches then just make sure that the highest bench is at least 18” above the top of the stones (so the foot bench for this highest bench is at or above the top of the stones). A ceiling at 48” (but no more) provides more comfortable room for using a vihta and as Risto Elomaa says “this is important”.

Some sauna builders in Finland told me that the area above the stones is löyly onkalo – ‘The Löyly Cavity’. It’s where löyly is.

Access to the benches can be via steps or a walking or access platform can be built 17-18” below the foot bench with steps up to it from the changing room floor. 

Bench Widths – Provide 2’ or 60cm of sitting bench AND foot bench per person. If a L shaped bench then a bit more so that the people in the inside corner don’t have their legs on top of each other.

A Bench to Lay On – At least one sitting bench should be at least 76-80” so that someone can comfortably lay down. 

Bench Depth – 24-28” is the recommended minimum as this is both comfortable for sitting and wide enough to lay down on. Lassi recommends as deep at 40” for the top sitting bench which is a good idea if you have space. If you have an L shaped bench then one 28” and one 40” would likely be ideal. If space is tight then narrowing the foot bench is the place to start.

Bench Board Gaps – About 1:5 air gap to wood. Gaps should be wide enough for good air circulation (3/8” minimum, 1/5 of the bench surface total) but not so wide (7/8” maximum) as to be uncomfortable to sit on.

Wood – Almost any wood can be used though some are better than others. Cedar is popular but can be too fragrant for some people and the oil in some cedar and other woods can be toxic though I’ve no idea how this plays out in a hot sauna. Avoid woods like pine with too much sap. Be careful of knots, especially for benches, platforms and backrests, as they can get much hotter to touch than surrounding wood.

Avoid plastic, vinyl, PVC, treated lumber or similar materials – When heated to sauna temps they can give off noxious gasses and worse these are often odorless so you do not realize you are breathing anything noxious. They are OK outside of the vapor barrier (and insulation). The goal of sauna is to be enjoyable, not to get cancer.

Be careful of Glues and Binders. These can produce unhealthy and unappealing fumes when heated. Glues and products such as OSB or Plywood should be avoided or minimized (though OSB sheathing that is on the outside of the envelope is fine). 

Groove Down – With T&G walls the tongue should face up and the groove down to avoid moisture, water or sweat collecting in the grooves. 

It Gets Hot – Be careful of any metals, woods or other materials that get hot easily as getting burned on these can be less than pleasant.

Warm Dry Floor – Stepping on to a cold or cold and wet floor while still in a hot room doesn’t make for a pleasant experience. A wood slat floor (duckboards) makes for a more enjoyable end to each sauna round. They will also help to keep benches cleaner as debris on the bottom of feet are more likely to remain on the boards or fall through them vs a hard floor where debris are more likely to stay on feet to be deposited on to the foot bench. Duckboards actually seemed quite rare in Europe as the entry to almost every sauna hot room was a step, followed by another one or three steps to get up to a platform and the benches.

Stove Sizing – Bigger is not necessarily better. Too high of kW results in shorter heating cycles, faster heating swings and less comfort. A properly sized heater will have longer run times which results in less noticeable temp changes and greater comfort. The EU recommendations from EU manufacturers should be good. Pay attention though to things like very large windows that may result in excess heat loss and require a larger stove. The more stones the better and more stones help to smooth out the temp swings.

Hygiene requires higher temps – It’s important that after a sauna has completed its duties for the day that heat is used to kill off bacteria and mold. The sauna should be able to maintain a minimum of 60°c (really 55°c but a bit of margin here is good) at the foot and sitting benches for a period of 15-20 minutes after use and after excess moisture has been exhausted.

Thermostat – Should be placed at about head height and not directly above the stove.

UL Labs: Promoting Unhealthy Sauna Since 1977 – In the U.S. UL Labs states that the thermostat should be placed directly over the heater and that temps should be limited to 90°c for electric heated saunas. This recommendation results in two problems; 1) Actual temps for bathers,  at their heads and shoulders, are then only about 60-80°c which is well below the 85-100°c temps recommended by the Finnish and Int’l Sauna Societies.

2) Most critical though is that this results in much too low of temps at the sitting and foot benches for good hygiene. Higher temps are needed to kill bacteria and prevent mold growth and UL labs prevents this.

Maybe avoid vaulted, coved or similar ceilings – In theory and in experience a flat ceiling is best as it results in the most even temps. Vaulted, coved or sloped ceilings result in heat being up too high and reduce fresh air movement. HOWEVER, I’m not convinced that it’s not possible to have something other than a flat ceiling that works and is comfortable such as a minor cove. A-Frames, Barrel saunas and similar shapes should be avoided though.

 

Stones 

More is better. MINIMUM 8kg / m³ (1/3 lb / cf) of space and 17kg (37 lbs) per person are good starting targets. More is better. 40kg (90lbs) per person is good. More stones result in more even temps, more even softer steam and thus a more comfortable experience. A good sauna is heated by the stones and the stones by the heater. Nothing makes up for proper stones.

Use virgin quarried stones – Landscape stones or river rock may have organic matter (think cow dung) that is unhealthy and can produce unpleasant odors when heated. Stones from along lakeshores can be good though if they are not under water constantly (if they have green stuff growing on them you don’t want them). Whatever you choose, wash them well with only water.

Rough stones are good – Stones should ideally have a rough surface to help hold tiny pools of water to make better steam. Smoother or rounder stones do not do this so well.

Warm New Stones Slowly – Stones may sometimes have pockets of water inside them. Three hours @ 50°c, 3 hrs @ 75°c and 3 hrs @ 100°c with a day or half of cooling down between without anyone in the sauna will allow the water to either dissipate or if the stone is going to explode do so without hurting anyone.

 

Ventilation

“Löyly is the Purity, Temperature and Moisture Content of the air contained inside the sauna as well as its thermal radiation.”
– 1988 Finnish paper on sauna health benefits

The primary goal of ventilation in sauna is removal of exhaled CO2 (and to supply combustion air for a wood stove). High levels of CO2, common in U.S. saunas, make saunas seem stuffy and cause bathers to exit because they need air rather than because they’ve received the benefits of heat and löyly. Secondary is to remove other impurities (both gaseous and particulate matter) from the air and circulate air to achieve as even and comfortable of heat as possible. In other words, our goal is Löyly. Steam added to bad stale air is just that steam added to bad stale air, not löyly.

Beyond make-up-air for the stale CO2 laden air that’s being removed, there is no specific need to bring in oxygen, there is a gob of oxygen in the air – it would be nearly impossible to run out of oxygen in a sauna even with high sauna temps. The problem in saunas is high levels of CO2 that result in feelings of fatigue, suffocation, brain fog or dizziness.

The following applies to electrically heated saunas and most wood stove saunas that are loaded and receive combustion air from outside of the sauna hot room (typically the changing room). Wood stove saunas with loading and combustion from within the hot room have some slightly different criteria.

Convection doesn’t work – If you have an electrically heated sauna you need mechanical ventilation using an electrically powered duct blower or similar. 1) Convection, even when working well, rarely produces sufficient airflow for a healthy environment and often zero airflow. 2) Convection relies on colder fresh air entering near the floor and being pulled upwards towards bathers as hot air exits higher up which results in significant temp stratification, cold feet and cool legs. 3) Convection is unreliable and changes with wind direction and speed, temp, humidity and barometric pressure. 

Powered exhaust has a number of benefits including downward airflow that helps to reduce cold feet, consistent and predictable airflow regardless of outside conditions, and the ability to have it freshen the air once a day when the sauna is not in use.

15-20 CFM per person – We want to keep CO2 levels at bathers faces below 700 ppm and ideally below 550 ppm. A general recommendation is a minimum of 15 CFM (25 m³ / hr) per person though DIN1946 says that 18 CFM are needed. Due to higher levels of CO2 in exhaled breath gyms often require 20-25 CFM per person however so sauna’s may similarly need somewhat more than 15-18 CFM but this needs more study.

Fresh air supply ABOVE the heater – Do Not put fresh air supply below an electric heater as this results in this cooler air flowing across the floor (hot air rises, cold air sinks) and making a direct path to the exhaust vent rather than providing any fresh air benefit to bathers. This also results in colder feet.

Air needs to enter in a way that it sufficiently mixes with the hot air and circulates up to bathers heads. A single vent above the stones should usually work fairly well. Better would be several smaller vents that result in a lower cold-air to hot-air ratio and so better mixing.

We are modifying the vent system in our electrically heated sauna so that we can try various combinations of supply and exhaust over the next few months (winter 2021-2022) to see what works best for maintaining good air quality (low CO2), comfortable temps from head to toe and so … Good Löyly. My guess is that a T shaped duct over the stove with a few small vents in the upright portion and a few in the top cross portion will be the winner. And similarly a horizontal duct below the foot bench with several small exhaust vents spread across it.

Exhaust below the foot bench – This has two benefits. 1) The rising flow from the fresh air supply above the sauna stones will then flow downwards across bathers faces and carry exhaled CO2 down (CO2 is heavy so wants to sink) to the exhaust vent. 2) This helps to pull warmer air downwards to lessen temp stratification and keep legs and feet warmer and more comfortable.

This exhaust vent should usually be on the wall opposite the stove and supply vent. Multiple smaller vents spread out along the wall below the bench may improve mixing and thus bather comfort.

Information in English is Wrong. Unfortunately, information available in English is very often bad advice:

Sauna airflow bad

Because physics doesn’t work like that. In reality the majority of the air will flow across the floor – it’s cold air, it likes being down low. Cold air is kind of like pouring BB’s or pellets out of the vent. A very tiny amount may flow in to the heater and some will rise up to envelope feet with cool air (and that’s not comfortable during sauna nor does it provide for proper heat afterwards to reduce bacteria and mold growth).Sauna airflow reality

Information in Finnish (and Swedish and German) says to do this (for good reason):

Sauna Ventilation electric heater

Sauna mechanical ventilation recommendation VTT 1992 SaunologiaFi

Sauna room ventilation uponor

The Technical Research Centre of Finland (VTT) conducted research on sauna ventilation in 1991-1992. They confirmed what many sauna builders in Scandinavia already knew and practiced. The following graphic from their research does a good job of summing up how different supply vents function.

Sauna

So…, I know EVERYTHING in English says to put the supply vent below the heater. Even Tylo/Helo, FinnLeo, Amerec, Huum, Harvia and other heater vendors say to do this in their U.S. manuals (when their other manuals get it right). But it doesn’t work. Physics says it won’t work and research proves it doesn’t work. The result is unhealthy and potentially dangerous levels of CO2 in U.S. saunas (besides experiences that fall far short of a proper sauna experience).

Also, CO2 is heavier than air and so naturally wants to sink. Ventilation flowing from high to low works efficientlyl with this but ventilation flowing from floor to ceiling is going against this and does not result in as much CO2 being removed.

5 Effective CFM is better than 20 Ineffective CFM – If your heater has difficulty keeping up with cold fresh supply air then reduce the flow rather than move the vent lower. 5 CFM entering above the heater that helps to reduce CO2 is much more beneficial than 20 CFM entering below the heater that does not reduce CO2 levels and adds to cold feet.

Multiple Smaller Vents Might Be Best – Ten 2” supply vents above the stones might work better than a single 6” as it will result in better mixing (better hot:cold ratio so less of the colder supply air will sink to the floor). Similarly four 3” exhaust vents spread out below the foot bench might do a better job of removing excess CO2 for all bathers than a single 6” that might work well for those directly above but not so well for those further away.

Maybe Pre-Warm The Supply Air – Bringing supply air in to the hot room below the heater and then having a metal duct run up the wall behind the heater to near the ceiling where it is exhausted will pre-warm the supply air and may result in better mixing, better CO2 removal and a more comfortable sauna experience. This isn’t critical but something to consider.

Clearing Exhaust in/near Ceiling – Include a clearing exhaust in or near the ceiling opposite from the stove and supply air. After the day is done this exhaust should be opened (with the stove still heating) with the blower running for about 15-30 minutes to clear the sauna of accumulated moisture which will help with keeping mold and bacteria at bay.

Duct Design – The smaller the duct the more noise from airflow (and the more static pressure) so somewhat larger is better. 4” round for up to 50 CFM, 6” for up to 140 is good. Make sure that the blower and nearby duct is mounted w/ perf strap or isolation hangers and that neither the duct nor blower contact any framing to prevent vibration noise from coming inside your sauna. A silencer (such as from Fantech) installed between your vents and blower can reduce noise a bit more.

Use Hard Duct – Flex duct results in high static pressure, often cannot tolerate the heat of a sauna and should not be used for exhaust ducts. Stretched tight and installed properly, it’s OK for supply air (and may be a good idea in really cold environments as insulated flex doesn’t have the condensation problems that metal duct does).

Blower Size – Blowers are typically rated for how many CFM or m³/hr they deliver. The marketing material will typically only publish what is called free air flow which is the blower without any ducting or wall caps that can reduce airflow. These things that reduce airflow are called Static Pressure. If you are familiar with Static Pressure then you should calculate the static pressure losses in your fresh air supply and exhaust ducts and choose a fan that delivers the desired CFM @ xx” Wg.  However, in most cases you’d likely be safe to simply choose a blower that has 150-200% of your desired airflow. A variable speed blower and controller are highly recommended.

Control – Controlling the exhaust blower with something like a Lutron Casetta provides a number of benefits. First is that it will allow for speed control of the blower so that ventilation can be adjusted to balance CO2 removal and heat. It can have a timer to automatically turn ventilation off a certain amount of time (20 minutes?) after sauna is done for the day. It can be programmed to turn on for some bit of time each day (20 minutes every morning at 7a ?) to prevent musty stale air when the sauna is not in use. On the latter it’s best if this can be done with a smart system of some sort so that it only does this automatic ventilation when supply air humidity will not be too high.

Measurement – Ideally we want to keep CO2 at bathers faces below 700 parts per million and ideally below 550 ppm. Measuring is difficult because CO2 meters don’t work well at sauna temps. We are working with a company on a solution but it’s still a ways out. In the interim there are a couple of options if you want to see how your own sauna does. First is to place a CO2 meter somewhere that temps remain below the max temp for the device (typically 60°c). In our sauna that’s on the platform below the foot bench. Many or most home devices do not provide accurate readings however those from CO2meter.com, IQ Air, and Awair (version 2 or later) have proven reliable. Avoid Foobot. Note that the actual CO2 level at bathers faces is generally a bit higher so adding 10-20% to readings might be good.

The second alternative is to heat your sauna to a temp that is safe for your meter to be closer in proximity to bathers faces and then doing three rounds of ‘cool sauna’. It’s important to find friends willing to do this so that you have as many people as you’d normally have. CO2 is multiplicative so 4 people exhale about 4x as much in to the room as one person.

 

Other Thoughts

A shower is important – It’s important to shower (and dry off) before first entering sauna and a cool shower is often a good way to cool off after each round. The more convenient the shower the more likely it is to be used and the more pleasant an experience. We have two for our sauna; one inside and one outside.

A Window on the world – Being able to see outside while in sauna is quite enjoyable.

Changing Room – Besides changing and showering this space provides a critical air-lock function to prevent or lessen cold chilling air from blowing in to the sauna.

A Large Changing Room – The changing room can be a great place to relax, enjoy a Finnish Long Drink, read a book or take a nap. Making this a larger area is never a bad idea.

A Covered Porch – When it’s raining or snowing it’s nice to be able to go in and out without the weather blowing in to the changing room and a sheltered place to sit outside to cool down is quite wonderful. We don’t (yet!) have a covered porch and wish we did.

Heated Floors – If you have a concrete floor then adding in-floor radiant heat can make for a more comfortable experience, especially in the changing room and shower but also in the hot room. Extending this to the porch and nearby walks or patios (snow melt system) isn’t a bad idea either.

Privacy – Sauna is best enjoyed nude. Providing for some privacy for both inside the sauna building and for an outdoor patio can make for a much more enjoyable experience for all.

Four is better than One or Two?  Consider at least a four person (8’ benches) sauna. One of the joys of sauna is socializing and enjoying it with others.

Wood, Gas or Electric Heater?  Wood is more traditional and more romantic. Even the routine of preparing the fire has benefits and for many of us is quite enjoyable, relaxing and a great way to prepare for a good day of sauna. A wood sauna causes you to slow down a bit and be intentional about your sauna which is good. Drawbacks are that it is not as convenient, uses natural resources (trees) and is a direct source of pollution. 

Electric is certainly more convenient, especially with a phone app that allows you to begin preheating before you arrive home and electric maintains more even temps. Electric may be less healthy, this perhaps due to the calrods used for heating (though this, if it is a problem, could be eliminated with better heater design). Electric may have similar environmental impacts to wood though as resources are used to produce electricity and production of electricity often produces pollution (and making solar panels does as well). How the environmental impacts of wood vs electric compare is a much longer discussion.

Gas is not as prevalent but can be a good option. Some local codes will not allow remote app control.

Hybrid. I built a hybrid gas/wood fireplace for our house. Natural gas is used primarily to get the wood going but is sometimes kept on if wood is greener than it should be. Similarly, it should be possible to create a gas/wood hybrid sauna stove that can act as a traditional wood stove (with a convenient gas starter) or have the convenience of a gas stove when desired. 

Mind The Gap – If you use radiant foil or foil faced polyiso as a vapor barrier (and you should us one of these and ideally the polyiso as it will reduce heat loss from thermal bridging) then you should include an air gap (0.5 – 0.75”) between the foil and interior wall boards using furring strips. There are three important reasons for this; 1) No gap could result in increased thermal bridging (heat loss in your sauna), 2) so that the back side of the wall boards can dry out and 3) so that the radiant foil can provide some radiant benefit. If there is no air gap then the foil does not act as a radiation barrier and does not reflect heat back towards the sauna. The air gap is critical for this. Done properly the walls of your sauna will be perhaps 10-20° warmer and so radiate more heat which means a more comfortable experience. Details on this in Lassi’s book below.  So…

Not So Good or Bad – Foil with no air gap

Good – Foil with an air gap

Best – Foil faced poly-iso with an air gap.

 

Barrels:

Avoid Barrels – These provide a poor sauna experience. Or, they don’t provide a sauna experience at all. Bathers often do not experience sauna temps (85-100°c at head and shoulders, no more than 15° cooler at feet). The heat is above bathers heads, uncomfortably cold feet and chilly backs can’t be avoided, and no changing room so every time the door is opened everyone gets a fresh blast of cold air and a bunch of what heat there is inside escapes. Most lack insulation which results in wasted energy but most importantly the walls are significant heat drains and so feel cold to bathers backs. The problems with cool temps lower down also creates bacteria and sometimes mold problems as they don’t get hot enough to kill them. More: 10 Things About Barrel Saunas.

Improving Ventilation and Cold Feet – Fresh supply air vents below the heater and exhaust higher up is a recipe for a not so good  experience. It results in colder feet and does little to remove the CO2 that people are breathing. Instead, try 4 small 2.5” fresh air supply holes above the heater (aligned vertical or slightly staggered, beginning about halfway between the top of the stones and the ceiling and evenly spaced). And then powered exhaust below the benches (or ideally below the floor) on the opposite end. Figure about 15-20 CFM per person (so 60-80 CFM for a 4 person sauna). 

 

Important Resources:

Web Links:

Sauna Ventilation – Finding Good Pure Air 

Sauna Times Blog

SaunaLogia

 

EVERYONE building a sauna should read Lassi Liikkanen’s ‘Secrets of Finnish Sauna Design’. I’ve read over 20 books on sauna and sauna design. This is the best and most accurate I’ve found. I wish it had existed when we built our sauna as it would have saved me a lot of research time, a lot of headaches and two remodels.

 

Folks in the U.S. (and elsewhere?) may also want to read Glenn Auerbach’s ‘Sauna Build from Start to Finnish’. Some practical information for sauna construction. Link for it is on the SaunaTimes website (for some reason the link doesn’t work properly here and results in a really giant image). 

 

Other Worthwhile Books:

The Opposite Of Cold (Nordskog & Hautala)

Cathedrals Of The Flesh (Brue)

The Sauna Is (Hillala)

Sweat (Aaland)

Sauna Magic (Conover)

 

Still To Learn:

We see extremely high particulate matter (1.0, 2.5 and 10.0) when ladling water on to the stones. Part of this and possibly all of it is bits of stone breaking off and disbursing with the steam. I’d guess some of it is also from the calrods which isn’t good.

We’re still trying to figure out a good reliable way to measure CO2 near bathers faces during a sauna session. It’s easy to do at lower temps like 60°c but not so much at 90°c which is above the temp range for most meters. Airflow will be different then too so why I’d like to find a good way to measure it.