Trumpkin’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. and North American sauna vendors, and that there are a lot of details that are critical to get right and easy to get wrong.

Everything in English – books, forums, Reddit, Facebook and websites – consistently recommended ceilings no higher than 7’, benches too low, ventilation that the laws of physics say won’t provide any ventilation and other things that just didn’t make sense. But when we searched in Swedish, Finnish and German we got much different information and information that does make good sense. Why such a difference?

We traveled to Finland and Sweden (my wife is Swedish) to experience sauna and learn from experts. We noticed a huge difference between saunas in the U.S. and saunas in Europe. Sauna’s in Europe are consistently much better. We wanted to know why. Why are saunas that U.S. vendors sell so much worse than even bad saunas in Finland?

The following is largely my notes from 2017-2019 as we were designing and building our sauna. Most of this (and the other Trumpkin’s Notes linked in the menu above) are not actually anything new but things that have been well known in Finland and elsewhere for decades. These are only new in the english speaking world.

I dislike people being misled or taken advantage of (I have Asperger’s and this is one interesting key bit of it). I hope that this information will help others to avoid the mistakes that we made or almost made.

Disclaimer: I am not an engineer nor doctor. Nor any kind of expert on sauna. 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 and in particular to read Lassi Liikkanen’s ‘Secrets of Finnish Sauna Design’. And if there is anything inaccurate below please let me know so that it can be corrected.

Trumpkin? One of my favorite characters in Chronicles of Narnia.

For a brief intro to Finnish Sauna and how to properly take a sauna: Intro To Sauna

 

What Is A Sauna?

A sauna is a wood lined room heated by a large mass of stones upon which water can be thrown to produce steam which when combined with pure fresh air and even heat around bather’s bodies results in löyly. The stones may be heated by wood fire, electric or gas.

That’s about it. One important thing I’ve learned is that you won’t find much of a detailed definition of what is, or is not, a sauna – a specification of any sort. How can we build a sauna without a spec? Without knowing what we’re trying to accomplish or aiming for? I even tried to get a spec written and received considerable, though very polite, pushback. Finns don’t want to box sauna in too tight. And rightly so.

What you will find is that saunas considered to be good in Finland all include certain details like a lot of stones (a sauna is heated by stones and the stones by a heater) that you throw water on to control humidity, foot benches above the stones, fresh outside air ventilation for bathers, the ability to get to or above 100°c (212°f) for those who desire it. These are ideals that good sauna builders there consistently aim for. And for good reason – because each has a functional purpose – a reason for being done. Each one of these along with the other elements detailed below contributes to a more enjoyable and healthy sauna experience.

“There’s a point where magic happens. When the löyly is so good, so close to perfect, that you know you’re experiencing something special. The air is fresh and pure without suffocating levels of CO2, even temps surround your entire body head to toe and front to back, no chilliness of any sort, little or no radiant heat from the heater or elsewhere and soft warm hygroscopic wood all around. The temp is somewhere above about 94°c, perhaps above 100°c, and it is wonderfully refreshing. Fresh water is thrown on the mass of stones, the steam rises and your entire body is enveloped in löyly. This is sauna.”

Sauna builders in Finland have a clear target that they aim for. They will do everything they can to get benches at the best heights, ceiling shape as perfect as possible, excellent ventilation, and on and on. And they very often hit their target. 

SaunaPolar05

Occasionally though, constraints force compromises – and good builders then do the best they can within the constraints placed on them. And that’s OK. Not meeting these 100%, being further off the mark, doesn’t necessarily mean that something isn’t a sauna, just that it’s not necessarily a good sauna so may be a lessor or different experience. 

Too often North American consumers are not provided the information to make good choices. We buy a kit or hire someone to build a sauna for us and it’s built to often misguided American beliefs rather than Finnish ideals. We’re told it’s a ‘Finnish Sauna’, but it rarely is. And this is all without any discussion. That’s not right.  

If someone in Finland wants a high peaked ceiling in their sauna a Finnish builder will push back quite hard and explain to them the negative effect that will have on the sauna experience. Many Finnish (and Swede, German, Dutch, etc.) builders will not build such a structure. Builder’s in the U.S. will often simply say ‘sure’ and do it – because either we don’t understand the physics of sauna and how poor an experience that peak will cause or our macho don’t-sweat-the-details attitude kicks in. Either way the result is a bad sauna.

Sauna builders and vendors in the U.S. don’t know what target to aim for. We’re intentionally aiming for ceilings no higher than 7’ and small spaces when sauna builders elsewhere are trying hard to avoid those because they know they result in a bad sauna experience. We need to start aiming for the same ideals as Finnish and other builders.

 

Löyly

Löyly is a Finnish word with no english equivalent and it is critical to a sauna.

Löyly is what a bather experiences when the temperature at their head and shoulders is about 85 -105°c and maybe ± 10°c. (185-221°f ± 20°f) and is fairly even around their entire body – head to toe and front to back. The air is pure and fresh without high levels of CO2, colognes or other contaminants. Direct radiant heat is very minimal so bathers are heated evenly by convective air all around their bodies. Ample soft wood walls and ceilings help to maintain a comfortable environment and absorb some noise so that the sauna is quiet and peaceful.

Water is thrown on a proper mass of stones producing a burst of invisible steam that envelopes bathers bodies for a brief period of two to three minutes and is then quickly exhausted returning the sauna to its original drier state – so that the burst can be comfortably repeated.

That is Löyly.

But there’s a bit more to it. If a Finn visits my cabin and we go to my new sauna building down by the lake together but the foot bench is below the top of the stones and so below the löyly cavity and so they know that they’ll have cold feet, then they’ll know that they will not experience löyly in my sauna. 

However, if we visit the sauna in my small 3rd floor flat and it has similar too low of benches my Finnish friend will proclaim it good löyly. Even though they might have had cold feet. What gives? 

The difference is that in my flat they knew that I had space constraints with no option to build it higher or larger so I did the very best I could. I showed perhaps, a very tiny bit of Sisu. I persevered. At my cabin I could have built a proper sauna with proper bench heights, the sky is, somewhat literally, the limit. But I didn’t, I took the American pseudo-sauna shortcut. Just the opposite of Sisu. 

As Jesse Hämäläinen of Narvi Sauna Heaters said “There is no shortcut to löyly”.

 

We Don’t Know What We Don’t Know

I thought I knew what good sauna was but it was not until I experienced a lot of proper saunas in Finland that I realized just how bad saunas in the U.S. are.  Glenn Auerbach thought he knew good saunas until he was surprised that he never got dizzy in saunas in Finland. I’ve known people who were positive that the sauna they’d built 10 years ago and used multiple times every week since was a great sauna . …until they fixed the ventilation.

U.S. saunas are like freeze dried instant coffee. Great …until you try the real thing. 🙂 

Many people will build a ‘North American’ sauna where they experience stale air and cold feet, and be quite happy with it. We’ll think that we’re experiencing good sauna because we don’t know any better. And if we’re happy with it that’s actually OK.

The problem is when we invest a lot of time and money in building a sauna and then learn how bad it is, that it’s not the Finnish sauna that we thought, that there are much better options. We were misled by vendors advertising ‘Finnish’ sauna. This happened to us.

 

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 bad information, a love of mediocrity and don’t-sweat-the-details, and a lack of sisu. U.S. traffic engineers not sweating the details on road design is why we have the most dangerous road system of all developed countries, why a child in the U.S. is 11x as likely to be killed walking or riding a bicycle as a child in Europe and why children in the U.S. don’t walk/bicycle to school as children in healthier and more academically successful countries do. One of many examples for why we have, not just mediocre, but the lowest life expectancy of all developed (and many third-world) countries. Details can be quite important.

We think that cold feet and feelings of mild suffocation are normal for sauna, but they’re not. These are only normal in poorly done saunas, most of which are in the U.S. (though it’s been pointed out to me that there are also some poorly designed and built saunas in Finland as well).

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 always above the stones if possible. 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 though 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. 

“Steam added to bad stale air is just that, steam added to bad stale air, it is not löyly.”

These details are more critical for women. Women are often 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 not so much.  This is why so many saunas in the U.S. fall in to disuse – they are not that great of an experience.

Those same 20 people experiencing proper sauna; 9 men and 9 women enjoy it and can’t wait until the next time. These are the saunas that get used frequently forever.

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

 

Building Or Buying A Sauna

SaunaLaws

Whether buying a kit, building from scratch or having someone build it for you, here are some critical things to look for. These are the things that are most often done incorrectly in North America and that are the cause of the “90% of saunas are bad” statements.

– Foot bench should be above the top of the stones and/or lower third of the space. 

– Proper ventilation (for electric: fresh supply above the heater, stale exhaust (mechanical) below the foot bench).

– Proper amount of stones. MINIMUM 6kg / m³ (1/3 lb / cf) of space and 17kg (37 lbs) per person.

– Minimum volume of 2 m³ (70 cubic feet) per person plus 1 m³ (35 cf) for the heater.

– Vestibule, often a changing room and shower, to provide an air lock.

– Proper vapor barrier and insulation.

If buying a kit, also be cautious of people capacity. Some manufacturers will advertise a greater capacity than the sauna can actually accommodate.

I strongly recommend against any barrel less then 8-10’ in diameter. More here: Notes On Barrels.

IR is not sauna. Nor can IR be combined with sauna as the IR panels reduce the amount of wood surface needed for a sauna and when used as a sauna the IR panels radiate heat which is uncomfortable and something you do not want in a sauna. Finnleo offers an InfraSauna that attempts to combine the two but the result is a quite poor sauna experience. More: Notes on IR Booths and Cabins

Some reviews of sauna kits: Kit Sauna Reviews

 

Cost

Costs vary considerably so for the most part every project is different.

First, doing a lower ceiling, lower benches and lessor ventilation, taking shortcuts for an American psuedo-sauna, will save only about 3-5% but will result in a much worse sauna experience. It’s not worth it. The lower ceiling will in most cases also cost more in energy use per session due to the smaller heat cavity. 

It’s possible to build a typical Finnish cabin sauna with an 8’x8’x8.5’ stove room, 8’x12’ vestibule/changing/shower and porch for about $12k (DIY) or you can easily spend $80k to have someone build it for you with nicer materials, finishes and details. A DIY build of a smaller 6x7x8.5 garden sauna can be done below $5k (2022 $’s) and then a vestibule/changing/shower added later.

Nicer aesthetic elements are often the biggest driver of high cost. The tile I wanted to use in our shower would have cost about $1300 more than the tile I ended up choosing. Doing decorative wood designs can easily add $5k or much more in labor.

While insulated frame construction is best, there are some significant cost savings to be had in doing thin timber (2.5” – 4”) walls and I’d take a well designed thin timber sauna over no sauna any day. A hybrid of all walls being thin timber except the primary bench wall could provide some cost savings and somewhat eliminate the biggest downside to thin timber which is bathers having chilly backs. A thin timber cabin with proper bench heights and ventilation could be a great starter sauna.

 

Sauna Heat Zones

There are two powerful forces at work in a sauna; heat stratification and convective loops. These result in three critical zones. 1) The Cold Zone is about the lower third – cold air needs a space to sink to and this is it. We want to avoid any of our body being in this area if possible. 2) Sauna builders in Finland call the area above the top of the stones Löyly Onkalo, the Löyly Cavity. This is above the top of the stones and above the cold zone and is where the primary convective loop of warm air is and this is where we want every part of of our body to be. 3) The area above the door opening is the Heat Cavity. This is an area that contains and preserves heat when the door is opened.

SaunaHeatZones01b

Here’s that convective loop that makes the Löyly Cavity so critical. There is another lessor convective loop of air flowing down a bit lower to the bottom of the heater but it’s only about 5% as much airflow as the upper loop.

SaunaConvectiveLoop1

A quick note on ‘cold’. Cold is a relative term. In a sauna the ‘cold zone’ is actually quite warm, perhaps 50°c (122°f) on average. But compared to higher up where we’re sitting in 90-110°c (194-230°f) temps it feels quite cold. It’s similar with ‘cold feet’ or ‘cold backs’. Temps at the foot bench might be 50°c (122°f) which in a normal room would be hot but if our head is in 94°c (200°f) air then our feet can feel cold at 50°c. We won’t notice a head to toe difference of less than 15-20°c but most people will begin to notice differences greater than that though sometimes we’ll not really think about it. Many people have said that they don’t have ‘cold feet’ in their sauna but then after raising their benches and fixing their ventilation have a revelation of what they’d been missing and how much better a sauna can be when the head to toe differential is decreased.

This knowledge of the heat zones and what happens in a sauna will help us to determine the best dimensions, bench and ceiling heights. In general we’ll want a somewhat larger room and higher ceiling for seven reasons;

  1. Getting the foot bench and so all of our body above the top of the stones and in to the löyly cavity.
  2. Getting us above the colder lower third of the sauna (sometimes more important than ‘above the stones’).
  3. Having sufficient overall volume of space per bather.
  4. Creating a large Heat Cavity for greater comfort
  5. Reducing direct radiant heat from the heater and stones.
  6. Reduce mold and bacteria on the foot bench.
  7. Reduce energy loss/costs.

 

The Notes – 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 ideas and patience in answering my endless questions and their perseverance in making sure that I not only built a proper sauna but understood sauna.

Hot Room Space – Minimum of 2 m³ (70 cf) per person plus one m³ (35 cf) for the elf (technically for the heater so yes, it is important).  Larger (like 3-4 m³ per person) is better, smaller not. The more volume per person the fresher the air will be and the less colder air ratio needed to maintain healthy air quality and löyly. Smaller spaces can also have people walking too close to the heater increasing the possibility of accidentally getting burned.

A good starting point recommendation from Lassi Liikkanen for a basic four person sauna is an 8’x8’ interior floor space and 8’4” interior height resulting in 130cf/person (3.5 m³ / person). This is comfortable for 4 people, benches aren’t too close to the stove, gets the foot bench above the stones for most stoves, provides a good heat cavity and it will be easier to maintain good air quality.

Reduce Harsh Radiant Heat – Space between bathers and the stove, perhaps about 1 – 2m (5′) or more, is a good thing. While the radiant heat in a 120°f IR cabin or from a ceiling heater on a 45°f patio will feel quite nice, radiant can feel harsh in the higher temps of a sauna. Radiant is also uneven and heats us only on the side its coming from. In a sauna we want to be heated evenly all around by soft convective heat and löyly. This is also one reason why having the foot bench above the stones is important.

Bench and Ceiling Height Are First Determined By The Stones – Temps are much more consistent, stable and comfortable above the top of the stones, in the löyly cavity, than below. (We also want our feet to be above the bottom approximate 1/3 of the volume of the space which foot bench above the stones usually accomplishes.)

START with setting the foot bench at or somewhat above the top of the stones. 4” (10cm) above is good, 12” (30cm) is better. Higher still if a larger heat cavity is desired. The sitting bench then is 17-18” (45cm) above the foot bench and the ceiling 42-48” (100-122cm) above the sitting bench. Someone sitting comfortably upright on the sitting bench with their feet on the foot bench then have their entire body up in the löyly cavity above the stones and have room to use a vihta.

A good starting point might be Foot Bench @ 34”, Sitting Bench @ 52” and Ceiling @ 100”.

If you’re building outside then you’re good to go. If inside and this is higher than your maximum ceiling height then you can play with things to get the best outcome. Buy a heater that can be lower perhaps or tighten up the bench and bench to ceiling heights a little but try not to have bench heights below 16” (41cm) or bench to ceiling less than 42-44” (100-110cm).

Access to the benches can be via steps or a platform can be built 17-18” below the foot bench with steps up to it from the changing room floor. If room allows, three benches can be beneficial and especially if the middle of these, that is both a sitting bench itself and a foot bench for the highest bench, can be a bit extra deep like 26-30” to provide more comfort for feet and rumps.

American Pseudo-Sauna – There is a misguided belief in the U.S. that sauna ceilings should not be higher than 7’. This is quite incorrect. The chart below shows one reason why Finns say it is so important to have the foot bench above the stones and why a higher ceiling is better than a lower ceiling. ‘Feet above the stones’ is critical to a good sauna. It was originally mentioned by Sakari Pälsi in his 1961 book ’Sauna’ and has been included in Finnish RT Specifications (guidance for building) since at least 2006.

The higher you are in the space the less of a head to toe difference you’ll experience and the more enjoyable your sauna will be. Your feet are 19°f warmer (40°f warmer than a 7’ barrel) and so 19°f closer to your upper body temp in a sauna with an 8’ ceiling than one with a 7’ ceiling. That simple 1’ of extra height makes a huge difference in comfort and enjoyment. The more even head to toe temps are the more comfortable and enjoyable a sauna is.

SaunaHeat

No matter how high the ceiling is, the temps near the top and bottom will be about the same given other conditions (fresh supply air, heater, changing room or outside temp…). If the temps are 100°c top and 40°c bottom in a 7’ high sauna then they will be the same in a 9’ or 10’ high sauna. Raising a 7′ ceiling by 16” to 8’4” allows bathers to also be 16” higher and so not just have better warmth but more importantly have less of a head to toe temperature differential and so less likely to have cold feet. That their feet are above the stones helps even more.

Ventilation with fresh air supply below the heater that pulls colder air upwards will make stratification and cold feet worse. Good high to low ventilation with supply above the heater and that pulls warmer air down around our feet will lessen stratification a bit resulting in a more pleasant and comfortable experience. Do not count on ventilation or air movement to overcome too low of benches though – it can help but rarely overcome stratification.

Here’s an IR image of our sauna showing how quickly the air cools as you go lower. How cold do you want your feet?

SaunaIR01

Feet above the stones also increases heat felt evenly around your body from löyly and decreases direct radiant uneven heat from the stove. The former is more comfortable and less harsh than the latter. This is particularly important for bathers closer to the stove.

A ceiling at 44-48” above the sitting bench provides more comfortable room for using a vihta and as Risto Elomaa says “this is important”. If you’ll have taller people then perhaps 50” would be good.

A Lower Löyly Cavity – With open sided tower or mesh style heaters such as from Iki or the Harvia Cilindro or Tylo Himalaya you can cheat the foot bench down below the top of the stones a bit if necessary so long as it’s still above the Cold Zone (lower approximate third where colder air is). The bottom of the Löyly Cavity can be bit lower with these heaters, particularly in larger rooms. It still may not be as comfortable as being above but with proper high to low ventilation it can be acceptable.

Large Heat Cavity Above The Door – Every time the door is opened some heat escapes and it’s the heat from the top of the door opening downward where this happens. Heat and löyly that are above the door opening largely remain in the sauna (think of a cup of air inverted in a tub of water). The larger and higher this cavity the better.  Being larger means that a larger volume of heat is retained within the sauna and a lessor percent is lost with each door opening. Being higher results in the hottest air being retained and cooler lost.

A 7’ sauna with a 6’6” door will loose 190°f air while protecting only about 6% of the heat while a 9’ sauna with the same 6’6” door will loose 181°f air while protecting 26% of the hottest air. 

In practical terms bathers will feel less colder air directly, the overall sauna temp will decline less and the sauna will recover to proper temps sooner. Overall much less discomfort for bathers. This can help any sauna but the more people coming and going the more critical it is. So if you will have many guests then a 9’ or 10’ ceiling might be considered to allow for a larger heat cavity. Keep in mind that if you raise your ceiling for a larger heat cavity then you need to also raise your benches. The upper sitting bench should always be within 40-50” (ideally 44-48”) of the ceiling and the next bench no more than 18” below. Besides the larger heat cavity this will also reduce head to toe stratification so is overall not a bad thing.

In saunas that will have many people coming and going, such as public saunas, a builder will try to have the foot bench and often the platform in the heat cavity above the top of the door (so a platform at about 6’6” or higher and ceiling at +12’ vs changing room floor). This can also allow for a door directly to outside since bathers are fully in the heat cavity and so protected from cold air entering when the door is opened.

A 7’ Ceiling DOES NOT Save Energy – The 7’ myth likely originated with the energy crisis of the 1980’s, a misunderstanding of sauna, misunderstanding of physics, and nobody ever questioning it. In a typical room where we sit near the floor and want to remain comfortable at body level then a higher ceiling requires considerable extra heat above our body to remain a comfortable temp at our body that is in the lower and cooler part of the room. A 7’ high ceiling needs to be about 70°f at the ceiling for our body to be 68°f but a 9’ ceiling will need to be much warmer, about 74°f, at the ceiling for that same 68°f temp where we are. That extra 4°f of heat will cost more.

A sauna is quite different. Since we are keeping our body in the upper part of the space then any additional volume is added/subtracted lower down; some just above the top of the stones and some in the cold zone below us. Regardless of how high the ceiling is we still want the ceiling to be the same 210°f and we still have the same löyly cavity.  Example: An 8’6” sauna costs $1.08 to heat initially and then $0.42/hr to maintain that temp (8’x8’, R-20 insulation, 30°f outside temp) so $1.92 for warm-up and 2 hrs of use.  Lowering the ceiling to 7’ costs $1.02 to heat plus $0.40/hr for $1.82 or 10 cents less per session. And though much higher temps we are only heating a sauna for a portion of each day/month/year rather than constantly so energy use/cost will often not be an issue.

But there’s a more important bit. A higher ceiling gives us a larger heat cavity and less heat lost each time the door is opened. Depending on how often the door is opened and for how long this can and in most cases will make the higher ceiling with the larger heat cavity less expensive to heat than a lower ceiling. This is a key reason that commercial saunas often have the foot bench or walking platform above the top of the door – because it costs them less to heat.

And one more. Some people who’ve installed proper ventilation in electric saunas with a supply above the heater and a mechanical powered exhaust below the foot bench discover that turning the exhaust blower up pulls more warm air down resulting in warmer feet and a more comfortable experience overall. This is good, but they are often ventilating at a much higher rate than necessary for ventilation itself and so are wasting heat that would not be wasted if their ceiling and foot bench were at proper heights allowing them to have the same comfort with less wasted heat.

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 good rule of thumb is to measure seating capacity along the front edge of the foot bench.

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 – A minimum of about 1/6 of the seating surface should be evenly air permeable so about 5:1 maximum wood to air gap. 4:1 or 3:1 can work better. Gaps should be wide enough for good air circulation (minimum 3/8”) but not so wide (7/8” maximum?) as to be uncomfortable to sit on. A larger gap of about 1” at the wall that allows better airflow behind bathers can help keep bathers backs warmer (though shouldn’t be so large that all of the air flows there and none to bathers front). 

Too little air permeability results in less even heat on bathers bodies and increased mold and bacteria growth.

Removable Benches – Building benches so that the bench or a portion is easily removable may be appreciated when cleaning time comes. It’s often easier to take them outside for a good scrubbing than to do it with them in place. This is doubly important if you want to give them a light sanding as this will save you cleaning up sanding dust (which I can tell you that you will rarely get fully cleaned up in a sauna). Lighter weight removable panels that sit in a stronger structural frame are a good option.

Bench Skirts – It is generally best to not have skirts. Many people like to tuck their feet under the bench, especially if someone is sitting there, and they impede airflow. If you include skirts then recessing them back several inches behind the front of the bench can be more comfortable for bathers. They should also be at least 30% permeable (3:1 wood to gap) for airflow.

Foot Bench vs Platform – Many saunas in Scandinavia do not really have a ‘foot bench’. Rather you go up 2 or 3 steps to the platform and then there are sitting benches around the platform. In others you might go up a step or two to the platform and then there will be foot benches around the platform with sitting benches above them.

Below you step up to a central platform and then on either side (one side shown) is a second platform a bit above the stones around which are the sitting benches. There is no real foot bench. (Note the fresh air supply in the ceiling).

Sauna paarakennuksessa

Wood – The use of wood is functional more than aesthetic. First, wood is hygroscopic which helps to even out temp and humidity extremes to provide a more comfortable experience. Some wood remains cool to the touch, and importantly, softer woods absorb some noise to make for a quieter and more peaceful environment. Ideally you want about 75% of the wall surface area and all of the ceiling to be soft wood.

Almost any wood can be used though some are better than others. Softer woods are generally better than harder woods so you want the majority to be softer. Mixing for aesthetics works well though keep in mind that different woods expand/contract at different rates so always allow for that. Avoid using woods that get hot in places with a lot of skin contact.

Cedar is popular in the U.S. but can be too fragrant for many 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. Personally I like the smell of cedar but find that in a sauna it detracts from the sauna experience.

Spruce, Fir and Aspen are the most popular in Finland, Sweden and elsewhere. Be careful of woods like pine with too much sap or knots, especially for benches, platforms and backrests, as a knot with sap or pitch can get hotter to touch than surrounding wood, knots can pop out with hot/cold cycles and sap dripping from the ceiling isn’t too desirable.

Abachi and Linden/Basswood are good options for benches as they remain a bit cooler than some other woods.

A good discussion on wood: Why Nordic White Spruce

Avoid plastic, vinyl, PVC, treated lumber, spray foam insulation 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 may be OK in limited quantity 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 vapor barrier and insulation 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.

Floor – The ‘floor’ of the sauna hot room can be smooth cement. There is no need for anything decorative as it will either have platforms built above it or wood slat duckboards on it.

Floor Drain – A floor drain is recommended and some say is critical. My personal opinion is that it is definitely good to have but far from critical. The presence or absence will not affect the normal sauna experience in any way. Having a drain may make cleaning easier since you can just hose everything down. If you want to be able to wash in the sauna, throw a LOT of water on the walls and benches during sauna or pour a bucket of cold/ice water over your head (if you’ve never tried this, you should) then a drain is more critical.

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 then be deposited on to the foot bench. Duckboards actually seemed quite rare in Europe however 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.

Door Opens Out and Is Unable To Be Latched – This is primarily a safety thing. Anyone in the sauna hot room needs to be able to exit quickly and easily at any time with a simple push on the door. There should never be anything that can accidentally block the door (such as the door to outside from the changing room) nor should there be any type of latch that can accidentally be latched or as a prank.

Cognitive and motor abilities can decline quickly and suddenly with heat stress and this especially if CO2 levels are high from poor ventilation. This can make any effort beyond simple pushing difficult or impossible. 40-50% of sauna deaths (which are quite rare but still 40-60 per year in Finland) are alcohol related with falling asleep in sauna the number one cause. One person told me that being unable to exit is the cause of some deaths every year which baffles her because she said it’s difficult to find such saunas in Finland as they are all made with easy exit for safety. Someone could also die from CO2 poisoning in an unheated sauna with poor ventilation if they are accidentally locked in.

Stove Sizing – Bigger is not necessarily better. If interior height is tight then a smaller stove may get the stones down lower in relation to the foot bench providing a more comfortable experience while too large of a stove will have the stones up higher so bathers will have colder feet and actually be less comfortable with a larger stove than smaller. Too large of a stove, particularly a cast iron or similar, may also result in too much radiant heat on bathers that can feel harsh and uncomfortable vs heat from stones and löyly. 

Too high of kW may also result 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. A rough guesstimation is about 1.0 – 1.5kW per m³.

Hygiene requires higher temps – It’s critical 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 +65°c / +149°f at the foot and sitting benches for a period of 15-20 minutes after use and after excess moisture has been exhausted.

Bacteria thrive in temps between about 4°c / 40°f and 60°c / 140°f. Mold between -5°c and 40-55°c.  A sauna is an ideal breeding ground for both. Once bacteria or mold gets a start in a sauna the only options to get rid of it is heat or removal of the material. Chemicals, which you never want to use in a sauna anyway, have too large of particles to penetrate to the roots of mold or home base of bacteria. 

Thermostat – Normally it should be placed at a height equal to 1m above the upper sitting bench and at least 20cm away from the heater. This will provide an accurate temp for sauna bathers. In North America many people place the thermostat much lower as otherwise they have an American warm room instead of a sauna. This could violate UL and manufacturer guidelines though which may be problematic.

UL Labs: Promoting Unhealthy Sauna Since 1977 – In the U.S. and elsewhere UL Labs states that the thermostat should be placed directly over the heater, 4-6” below the ceiling and that temps at the thermostat 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 critically 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.

As well, UL may be requiring sauna heater manufacturers to include a high limit temperature switch on their heaters with a very low high temp limit. This results in a couple of problems;

1) Heater manufacturers appear to be requiring a low fresh air supply vent in order to cool the heater, HL probe or both in order to prevent trips. This low vent results in poor ventilation for bathers and so high levels of CO2 in U.S. saunas.

2) It is somewhat common for people in the U.S. to separate the HL probe from the heater to prevent constant trips. If the HL probe and switch is needed from an engineering standpoint rather than just to meet a UL requirement then this could be problematic.

UL’s requirements do not appear to align with those of other countries and like new wine in old wineskins may be doing more harm than good.

Maybe avoid vaulted, coved or similar ceilings – In theory and in experience a flat or near flat ceiling is best as it results in the most even temps. A slight rounded cove in the ceiling or angled coves in the corners can help airflow.  Heavily vaulted, coved or sloped ceilings result in heat being up too high and reduce fresh air movement. A-Frames, Barrel saunas and similar shapes should usually be avoided though.

 

Stones 

More Is Better. MINIMUM 6kg / m³ of space is a good starting target though several sauna builders I’ve talked with say 8kg / m³ is the minimum. More is better so 10-12kg / m³ is better up to about 16kg / m³ (or about 1/3 lb / cubic foot minimum to 1 lb / cf). Beyond that may be getting in to some diminishing returns so while perhaps still better, only marginally. More stones result in more even temps, more even softer steam and thus a more comfortable experience. More stones results in more negative ions which can make us feel better. A good sauna is heated by the stones and the stones by the heater. Nothing makes up for proper stones.

For perspective, a smoke sauna in Finland will have about 90kg of stones per m³.

Commercial Virgin Quarried Stones – Landscape stones or river rock may have organic matter (think cow dung) that is unhealthy and can produce unpleasant and unhealthy odors when heated and this can take years to burn out. There is also potential for stones to contain arsenic, asbestos, sulphur or other undesirable elements. Commercial sauna stones are assured to be able to tolerate heat and to be free of undesirable compounds.

Stones from along lakeshores can be quite good 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.

Olivine diabase are a volcanic stone that some Finns believe are the ideal option. Gabro and Peridotite are also good.

Rough Is 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 (though some people do prefer the much milder steam that these create). If you want the look of rounder stones then maybe use them only for the top layers. 

Bigger Is Not Better – Stones should be about 5-15cm (2-6”) in size. Surface area is important so too big of stones will result in too little surface area and too small of stones will disintegrate and not last long.

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.

Deeply Stoned – You want at least 3-4 courses of stones on top of each other so about 40cm or 16” of depth minimum.

Harvia has a good discussion on stones here.

 

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

Steam added to bad stale air is just that, steam added to bad stale air, not löyly..”
– 2020 Trumpkin’s Sauna Notes

Ventilation in a sauna is critical and discussed in: Proper Ventilation For Saunas.

DO NOT skip proper ventilation.

 

Other Thoughts

Location – Sauna, More Than Just The Hot Room – Sauna (verb) is not just sitting in the hot room and sweating. That’s actually a rather minor part of the overall experience. Sauna is hot/cold/hot/cold/hot/cold. Cooling off is just as important an element of each round as sweating. A sauna (noun) needs to be located where bathers can quickly and easily cool off each round. Ideally with a shower in an adjacent changing room and a door to outside. Being able to go outside each round if possible is quite important.

Social aspects and being able to invite friends to join in is also important. 

With these in mind. A sauna in a bathroom is totally fine and can work well for many people but that can be a long trek to outside and perhaps not the best social space. A sauna with an adjacent changing room and shower in a lower level might be better and a sauna building outside best.    

A Shower (or two) Is Important – A shower directly adjacent and without having to go outside in cold weather is almost critical. It’s important to shower (and dry off) before first entering sauna and a cool shower is often a good way to cool down after each round. Rinsing sweat off before going outside in cold weather is not a luxury. 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 (below) and one outside. In non-winter environs something as simple as a hose (or pre-made hose shower) on an outside wall can work.

Sauna05 100

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

Changing Room/Shower/Vestibule – Besides changing and showering this space provides a critical air-lock function to lessen cold chilling air from blowing in to the sauna. It also provides a safe way to lock the building without the risk of locking someone in the hot room. Sauna designers in Scandinavia shoot for this to be at least 1.5x the size of the hot room if possible. So an 8’x8’ hot room for 4 people will have about an 8’x12’ changing/shower/vestibule.

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. Or maybe even have a central gathering room with the changing/shower off one way and the sauna off another.

A Covered Porch – When it’s raining or snowing it’s nice to be able to go in and out without the weather blowing down 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.

One significant drawback to electric in the U.S. are the UL requirements and the problems they pose outlined earlier.

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. 

Some Perspective On Temps – The Finnish Sauna Society and International Sauna Association recommend temps of 80-105°c (176-221°f) or 85-100°c at bathers heads and shoulders (thermometer or probe placed 1m (39”) above the middle of the longest bench). Others say hot enough that 10-15 minutes is as long as you can stay in. The majority of Finns and Swedes I’ve talked with prefer 95-105°c with occasional warmer or cooler sessions. Dr. Jari Laukkanen’s study on the benefits of sauna bathing for cardiovascular health found average temps of about 78°c for participants (Finns, avg age 63). Russians seem to prefer either slightly cooler with much higher moisture (nothing like a steam room or hammam though) or much higher temps of 130-140°c (266-284°f) with lower moisture. My personal preference is 95-100°c most days with occasional 110-120°c days or sometimes longer rounds of 70-90°c. SO, there’s a lot of variety in ‘correct temps’.

A good electrically heated sauna then should be able to maintain any temp from 70-105°c or better to 125°c or higher.

I think that many people in the U.S. confuse bad air from poor ventilation with heat exhaustion. FWIW, I’m ready to leave a 90°c sauna with bad air after about 10 minutes and the last few minutes doesn’t feel too great. In a sauna with good ventilation I feel quite good for 12-20 minutes at +100°c and every second until I step out feels great. Good ventilation is critical to being able to get the most out of heat and löyly. Poor ventilation resulting in high CO2, common in U.S. saunas, can also result in Hypercapnia.

Fresh Water – You need water to throw on the stones for steam and to dump over your or mates heads. Since the Flint Michigan water incident many communities in the U.S. have been significantly increasing the amount of Chlorine and other chemicals in their water systems. These are quite bad in a sauna, especially when thrown on the stones. Make sure that your water supply filters these out or that you use something like a Berkey or RO system to provide clean unadulterated water.

 

Thermometers and Other Measurement Devices

Moved to: Notes on Thermometers and Other Measurements

 

Notes on Construction

Disclaimer: I am not an engineer nor a builder so I am far from any kind of expert on wall assemblies, but I do know a little bit about physics. 

Vapor Barrier – A solid vapor barrier is critical if the walls are not solid timbers. Many people say that a sauna is a ‘dry sauna’ but this is not really the case. 20% relative humidity in a 100°c sauna (actual moisture content ≈ 134 g water / kg air) is about 99% RH at 61°c and at temps below that is… water. For perspective, 90% RH at 26°c, a hot muggy day, is only about 19g of water / kg air. There is a lot of moisture in most saunas.

Saunas are also kind of high pressure; 1) The heat increases pressure (hot always flows towards colder), 2) heat rises and creates even higher pressure in the upper part of the sauna and 3) steam creates even higher pressure again. This higher pressure inside the sauna is pushing out against the walls and ceiling and wanting to take all of that moisture inside with it. If not stopped by a solid vapor barrier this moisture will condense in the insulation leaving the insulation wet which reduces its effectiveness and given the heat makes an ideal environment for mold. This will not usually dry to the inside or outside. It was driven in to the insulation by pressure and without similar pressure or airflow to drive it out, most of it will stay there. 

Insulation – Good and proper insulation in a sauna is important, not so much for energy efficiency as in a house, but for bather comfort. A wall that sucks a lot of heat out can make bathers backs feel cold relative to the front of their bodies and chilly backs can be quite uncomfortable (especially for women). We want to minimize this as much as possible. Well insulated walls provide for a better, more even and more comfortable löyly heat on all sides of your body.

Reducing thermal bridging through the studs is quite important to accomplish this. Traditionally (in Finland, Sweden, etc.) foil faced polyiso (such as FF-PIR) on the inside provides a good vapor and thermal barrier. Architect Christopher Wegscheid points out that environmentally this is not a good choice and a layer of mineral wool on the outside would be better. A proper rain screen is always important but critical with exterior mineral wool. Thick enough exterior insulation can eliminate the need for insulation between the studs however I’m not sure I’d do that for a sauna, especially in a colder environment. Attention must also be paid to the dew point and so condensation in wall cavities which varies by environment.

Thin Timber Construction – Thin timber construction (timbers less than about 5” thick) can save a good chunk of money. While a properly insulated and vapor-barriared sauna is definitely best, particularly in colder climates, I do think that given the cost and time savings that thin timber is not necessarily a bad option. Given monetary constraints it’s much more important to get benches at proper heights and have proper ventilation. Even with thin timber walls the ceiling/roof should be built with proper insulation and vapor barrier.

Mind The Gap – If you use radiant foil or foil faced polyiso / PIR (that meets temp requirements) as a vapor barrier (and you should use one of these) 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 and a colder more uncomfortable wall because the foil can act as a cold sink, 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 any heat back towards the sauna. The air gap is critical for this. Done properly the walls of your sauna will be a bit warmer than without the gap and so provide a more comfortable experience (more details on this in Lassi’s book below). So:

  • Best – Cladding + rain screen + exterior mineral wool (1-2” minimum) + studs and insulation + foil vapor barrier + air gap + interior T&G.
  • Better – Cladding + rain screen + studs and insulation + foil faced polyiso or PIR + air gap + interior T&G.
  • Good – Cladding + rain screen + studs and insulation + foil vapor barrier + air gap + interior T&G.
  • Not So Good or Bad – Foil with no air gap

Some perspective – Some people in the U.S. will say that the gap is not necessary. They’re likely correct. The gap provides some benefit to the sauna experience and possibly to the longevity of the sauna but it’s often minimal and not having the gap is probably not much of a negative in most cases. Similar to not having a drain. However, including the gap is inexpensive, quick and easy to do so why not.

 

Barrels:

Moved to: Trumpkin’s Notes On Barrels.

 

Form, Function and Löyly

What follows is about function and Löyly. It’s about the things that are needed for a good proper Finnish sauna experience.

Form is important also and form can enhance function. Sauna is more enjoyable in a room that is aesthetically pleasing than one that’s not. Should sauna function ever be compromised for form? Perhaps. But not for our sauna, the one we use several times per week. For our routine saunas we want as great a sauna experience as we can get.

Some people 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. Or the löyly is slightly compromised for an really amazing view. And that’s OK (and I’d love to come enjoy the sauna and the view). Saunas Of The World is one of my favorite Instagrams because I love architecture and it has some fabulous looking saunas and places, but many or even most of what they feature are either not sauna’s or not good sauna’s. I’d still love to visit many for a sauna though.

Someone may prefer to have all glass walls for instance, and that’s certainly OK. Or they may want lower benches. What’s important is that they understand what affect these will have so that they can make an informed choice – what bit of better sauna experience are they giving up for a better view or not having to climb up higher (and there are some great options for those with disabilities to be able to enjoy a proper sauna).

What’s important is not that every sauna be ideal, that it hits the golden bullseye above, but that people know and understand what compromises to the sauna experience are being made. 

 

Breaking The Rules

Sometimes constraints prevent us from achieving the sauna that we want and in these cases we simply do the best we can. Other times we might choose to intentionally break a rule or two to achieve an aesthetic element. And sometimes we can get away with breaking rules…

Case Study 1 – I’ve recently been involved in a conversation for a ‘campfire’ sauna. The owner wants a U shaped seating arrangement around a central pillar style heater that might have a bit of a campfire feel. I think that this is a great idea, even though it breaks some rules.

Here’s a photo of the sauna at Villa Furuvik just outside of Helsinki that is the inspiration for this project.

VF 01

Here’s why this works. First is that this is what some Finns refer to as a party sauna so while it should still provide a good sauna experience, that experience may be somewhat secondary to other aspects including social elements and being safe for people who might have had a bit more alcohol than normal. It’s important to note that this is retrofitted in to an older shed and so also had some unavoidable constraints including overall size and height.

So, let’s break some rules.

Feet aren’t above the stones. They are though above the cold zone which is more important here. ‘Feet above the stones’ actually sort of serves four purposes in one; 1) There is usually less stratification above the stones and the less head to toe temp difference the better, 2) getting feet above the stones also usually gets feet above the cold zone, 3) feet above the stones kind of forces the ceiling higher to create a heat good cavity and 4) feet above the stones reduces direct radiant heat.

VF 02b 100

The foot bench here is about 31” above the floor and so is above the cold zone. 

Even though the room is not perhaps as large as they would have ideally liked, it is still somewhat large, about 11’x10’. And, the heater is in the middle so there is even space all around to the walls. These two elements help with stratification. While in a typical smaller residential sauna the stratification changes quite dramatically at about the top of the stones, here it will continue down a bit before we start getting the more quickly changing air temps*. So while in a smaller sauna the floor of the Löyly Cavity is above the top of the stones, here it is a bit below.

And there is a fairly ample heat cavity above the door. 

Being above the stones might still be best but this will work relatively well so long as there is good ventilation to also help pull warmer air down.

Too close to the heater. Will people sitting here feel a lot of uncomfortable radiant heat from the heater? If they have the 12” diameter Tylö-Helo / Finnleo Himalaya that we have in ours, yes. Like with many sauna heaters you need to be about 4-7’ away from it for the most comfortable experience. The Iki in the photo and planned for the new sauna is 21” in diameter though and as Lassi Liikkanen (author of ‘Secrets of Finnish Sauna Design’, the book that everyone should have) points out, will have less radiant heat from the sides due to the much greater amount of stones (and that 21” width of stones).  While temps on the sides of the Himalaya can range from 100-150°c, the Iki doesn’t much exceed 100°c to the sides.

This sauna may not be one you’d want as your everyday sauna (though I could be wrong on that) but it should serve quite well as a party sauna and will likely be a better sauna experience than 99% of saunas in North America.

* An interesting bit for the techie folks reading this (and hopefully I’m not butchering this too much as it’s been about 40 years since I dealt with some of this)… This is the same principle that is used with line array speaker systems at concerts. There is pattern that we see frequently in nature called a cardioid. We see it with sound coming from a speaker, microwaves coming from a horn, and heat coming from a heat source. The back side of the cardioid is called the null or null zone. A wider heat source in a narrower room has a large, about 180° null of less heat – thus feet above the stones. As the room gets larger this null decreases (we move from a plane source towards a point source) which is what allows us to sort of get away with feet not being above the stones for this example. The same thing happens with heat sinks in… audio amps. A narrow heat sink results in a narrow null which results in components next to the heat sink getting hot. So, we’d sometimes use larger heat sinks to create a larger null and protect nearby components. It was this phenomenon that led an engineer at Clair Bros audio to do something similar with speakers. If you place two speakers next to each other you decrease the null. Do it again and you decrease it further. Line up enough speakers and you start getting a very narrow non-null pattern or more to the point a more directed narrow pattern. With waves (sound, radio, etc.) the narrowness has to do with the frequency relative to the size of the source. Heat is the room size relative to the size of the source. Other experiments with line array speakers were based on how microwaves respond to point/plane source.

 

Important Resources:

Web Links:

Sauna Ventilation – Finding Good Pure Air 

SaunaLogia

Sauna Times Blog

 

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.

_________

* If the vapor barrier is well sealed then there is not likely to be much or any moisture on the back side of the interior boards.