[DRAFT]

We know that sauna design affects bather tolerance and enjoyment. A larger space, higher benches and good ventilation result in an enjoyable and compelling sauna experience while smaller spaces, lower benches and poor ventilation result in saunas that are not well tolerated. These latter are called novelty saunas because once the excitement of newness, novelty, wears off, so to the use in many cases.

Sauna design and the resulting sauna environment likely also has a significant effect on physiological response and so health/wellness/recovery benefits.  Knowing details of saunas and other thermal interventions used in studies will help us to better understand what design elements result in what benefits and perhaps more important, what designs result in few or no benefits.

 

Sauna Design Effect On Physiological Response: ‘Sauna’ ≠ Sauna

There is likely a significant difference in the physiological response from a small box with low benches and poor ventilation that’s typical in the U.S. compared to a proper sauna with feet above the stones and good ventilation that’s typical in Finland.

A proper sauna should likely provide an increase in Tcore of ≈1.1 – 1.5°c after 15 minutes of exposure while a small, low bench, poorly ventilated Finnleo novelty sauna like that used in Atencio 2025 resulted in less than 0.2°c in 10 minutes.

The sauna environment that bathers experience is determined by two things. First is the design that affects things like how even the heat and steam are and how fresh the air is. This is for the most part fixed for a particular sauna. Second is the setup such as the desired temperature and humidity that can both be varied from session to session.

The resulting environment then affects both physiological response and bather comfort. Less stratification for example will result in both increased bather comfort and likely a higher Tcore.

Bather comfort itself likely affects physiological response as well as some direct affect on resulting benefits. Good ventilation that results in lower CO2 will allow bathers to be more relaxed and will result in a more comfortable, enjoyable and compelling environment. Instead of a sauna that is noted as not well tolerated and that people won’t do as often or at all, we’ll have one that people thoroughly enjoy being in and want to enjoy frequently for decades.

For stratification alone we can see that there are numerous design elements that will affect how much heat and steam stratification we have and this in turn affects numerous physiological responses.

Physiological response likely affects comfort as well. A higher Tcore likely makes cold plunge after a sauna more enjoyable. I’ve noticed on numerous occasions that a cold plunge after a proper sauna is much more enjoyable and tolerable than after a barrel or other low bench sauna.

So it’s important to know both the design parameters of the sauna as well as how it is setup. This in turn will provide for better knowledge of physiological outcomes, better sauna designs and more accurate and honest consumer information.

 

Documenting The Sauna:

Some key design elements that can make a difference and that are important to know include;

1. Interior:
1. Room dimensions
2. Door dimensions.
3. Wood type if known.
4. % of wall surface that is wood, glass, other.
5. Ceiling shape: flat, sloped, sloped in what direction, rounded, etc.
2. Heater:
1. Mfr, Model, kW
2. Stone load
3. Location in room
3. Benches:
1. Sitting bench height & dimensions
2. Foot bench height & dimensions
3. Size of air gap behind the sitting bench
4. Air gaps ratio in benches
5. Bench skirts?
4. Ventilation: 
1. Sizes and locations of supplies
2. Sizes and locations of exhausts
1. Type of exhaust; mechanical, passive.
2. Exhaust rates (in liters / second)
3. Any other known air entry points.
1.  
5. Commons Area / Thermal Suite:
1. Shower / rinse availability
2. Cool down options/procedures
3. Rest options/procedures

Photos: showing all walls, foot bench relationship to heater, ventilation supplies and exhausts, thermostat sensor location, locations of measurement sensors.

 

 

Measurements

Temperatures, humidity and CO2 levels can vary considerably within a sauna. For example, a thermostat mounted on the heater wall can provide readings 50-70% higher than actual sauna temps and 2x to 3x higher than bathers feet on the foot bench. So where measurements are taken within the sauna is critical. Just saying that a sauna is 90°c is almost meaningless without knowing where it was 90°c.

There are a number of measurements of the sauna environment that are important. The two most critical are the official sauna temperature and temperatures at the foot bench.

1. Official Sauna Temperature – Taken on the bench wall, 1m above the sitting bench, at least 20cm from either corner and 5-10cm out from the wall. This latter to avoid the cold layer air next to the wall.
2. Temperature at the Foot Bench – Taken approx 2-5cm above the foot bench and some distance from the heater.

These can vary considerably over time so it’s best to log the measurements (≈ 1 sample / minute). Then calculate an average during the exposure time if appropriate.

Absolute Humidity (g/m3) and CO2 are also helpful, particularly if logged over time.

 

A Recommended Sauna

 

 

 

 

 

 

Known Environment and Attributes

One other advantage to a defined standard sauna and baseline protocol is that we can fully analyze many aspects of this sauna from both a sauna dynamics and physiological response standpoint – we can get to know this sauna well. We can know in detail what ambient air temperatures and density of steam various parts of the body are exposed to.

This will help us to better understand variations; larger, smaller, higher elevation, etc.  

Corentin Macqueron is producing some valuable fluid and thermo dynamics models of a few saunas and having a standard like this will help him to produce better models.

 

 

 

 

Notes on Sauna Design – Why This Design:

The specifications listed are those most likely to affect physiological response.

 

The overall size will result in appropriately even temperatures and steam distribution.

The placement of the heater will result in a good convective loop that will provide more even temperatures and comforting evaporative cooling of bathers skin.

A larger sauna would likely be more comfortable and enjoyable and possibly provide greater health benefits

A smaller sauna will be less comfortable and enjoyable and likely provide lessor health benefits. We can be fairly certain for instance that the increased stratification on bathers bodies of a lower ceiling and benches will result in significantly less increase in core body temperature.

 

Similar standards should be established for other thermal modalities including bio-sauna, steam bath, IR treatment, Laconium, Tepidarium, Caldarium, Ultrasound, etc.

 

Note: this is not a one person’s design but an amalgam of best design practices from numerous sources, primarily the book ‘Secrets of Finnish Sauna Design’ and associated Saunologia.fi website.

 

 

Some Terminology

A Round is one continuous period in a sauna hot room (or steam bath, vitality pool, etc.) followed by a rest/rinse/cooldown period.

A Session is a collection of repeating rounds.

A typical sauna session might be 3 rounds, each round comprised of 15 minutes @ 90°c + tepid rinse + 4 minutes cold plunge @ 16°c + 20 minutes rest @ 22°c.

Total Session Heat Exposure is the total amount of time spent in a hot experience during one session.

Total Session Cold Exposure is the total amount of time spent in a cold experience during one session.

Degreetime is the sum of degrees celsius for each minute of exposure. This can be a measure of ambient air temperature, latent heat of steam, or core body temperature.

For example, a good sauna should result in an increase in Tcore of ≈1.5°c in 15 minutes. Ambient degreetime for this sauna would be about 1350 and Tcore degreetime about 573.

An IR device is slower to effect Tcore, taking about 2 hours, about 8x as long, to achieve the same 1.5°c increase. Bathers are likely to tolerate more time with this than a sauna however. Ambient degreetime here would be 5256 while Tcore degreetime would be 4592.

This might help us to better understand how time, temp, Tcore and peak Tcore affect physiological response. Can a Tcore increase of 1.5°c in a standard sauna provide the same benefits as taking 2 hrs to reach that same 1.5°c in the IR dome used for Mason 2024?  How about 3 sauna rounds over 2 hrs resulting in a Tcore degreetime of 2310?  And similar for effects of Tskin, Tmuscle, etc.

It’s important as well that everyone use common and accurate terminology for different modalities. For instance, in a sauna, by definition, bathers are heated by convective heat produced from heated stones and humidity is increased by steam produced from water on the stones. An IR device, be it a cabin, dome or individual panels, is not a sauna or any sort.

Some additional terminology and thermal taxonomy: https://localmile.org/thermal/

 

 

 

Some of this same rigor should be applied to other modalities such as steam baths, laconiums, tepidariums, etc.

 

As well, a Baseline Usage Protocol.

 

Revisions:

2025.07.31 – First Draft

2025.089.02 – Second Draft