Draft Proposal For A Standard Sauna For Research

It’s quite difficult to communicate effectively when we all have different understandings of what words mean.

A sauna for instance …is not necessarily a sauna. This especially in the U.S. where all manner of hot boxes are called a sauna.

A problem with medical research regarding saunas then is inconsistency with regard to the sauna used. This is a problem because there is likely a significant difference in the physiological response from a small sauna with low benches and poor ventilation that’s typical in the U.S. compared to a sauna with feet above the stones and good ventilation that’s typical in Finland from where we get the word sauna.

Similarly, different use protocols are likely to produce significantly different outcomes.

The current environment is akin to a study where participants are given ‘drugs’ with no specification of what drugs were given. Just saying participants were ‘in a sauna’ is kind of meaningless. In some cases the ‘sauna’ in a study may not even be what most in the world consider a sauna and not likely to deliver the same benefits.

This is also misleading for consumers who may think that they are getting X benefits from their novelty kit sauna when in reality they are not. This only empowers bad actors who are then able to take advantage of consumer ignorance and make all sorts of claims that ‘sauna’ provides X benefits when that is likely not the case.

This is by the way, nobody’s fault. I’m only aware of four people in the world studying sauna physics at this level and none of us are doctors nor medical researchers.

Following is a proposal for a Standard Sauna and Baseline Usage Protocol.

 

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.

 

A Standard Sauna:

The sauna specified here should provide a good, comfortable and enjoyable sauna experience for bathers, healthy air quality and appropriate increases in core body temperatures and other measures. The bather experience and health benefits should be consistent with good saunas in Finland and other areas of Europe. And considerably better experience and benefits than typical saunas in the U.S. 

  1. Interior 
    1. Dimensions: 250 cm x 250 cm x 260 cm high
    2. Wood: Spruce or pine. Preferably nordic spruce. 
    3. Ceiling Shape: Flat. Rounded or flat coves in the corners would be beneficial but not necessary.
  2. Heater: 10.5 kW Helo Laava or 10.5 kW Narvi Ultra located adjacent to the wall opposite the bench wall.
    1. Approximately middle of the wall opposite the benches for a side entry door. Approximately centered between the door and side wall for a front entry door. 
  3. Benches:
    1. Foot Bench: 250 cm x 40 cm @ 90 cm high
    2. Sitting Bench: 250 cm x 70 cm @ 130 cm high.
      1. Include a 5-10 cm open air gap between the bench and bench wall.
    3. Air Gaps: Benches should be air permeable with 
    4. No Bench Skirts.
  4. Ventilation: Mechanical Downdraft. 
    1. Passive Supply: 200 cm2 face area vent
      1. located in the ceiling and centered 10 cm closer to the bench wall than the center of the heater.
      2. Or located on the heater wall, centered on the heater and 20 cm below the ceiling.
      3. Passive supply includes back flow prevention of either an updraft duct, passive flapper gate or similar.
    2. Mechanical Exhaust: Located 30 cm below the foot bench (60 cm above the floor).
      1. Blower should be speed adjustable and able to produce at least 50 l/s of airflow for the completed sauna.
      2. The blower should be mounted for as quiet of operation as possible including mechanical isolation from the structure and the use of a silencer between the exhaust vent and blower
    3. No other air entry points.
  5. Door: 60cm x 200cm
  6. Measurement:
    1. Sauna Temperature: On the bench wall, 100cm above the sitting bench and 30 cm from the corner furthest from the heater.
      1. Probe sensor must be at least 10 cm from wall to avoid cold layer.
      2. [Is this still best location after Lassi experiments?]
    2. Temp/Humidity Sensors: Located on the bench wall in a line 60-90 cm from the corner furthest from the heater.
    3. Heights (in order of priority): 
      1. Head: 100cm above the sitting bench.
      2. Feet: 10 cm above the foot bench (on a bench support). 
      3. Sitting: 10 cm above the sitting bench.
      4. Calf: 25 cm above the foot bench (on a bench support).
      5. Low Back: 40 cm above the sitting bench.
      6. High Back: 70 cm above the sitting bench.
    4. CO2 Sensor:
      1. Std Temp Sensor (50°c): 30 cm below the foot bench in line with exhaust vent.
      2. High Temp Sensor (>80°c): 20 cm above the sitting bench or near bather faces if possible.
  7. Commons Area / Thermal Suite:
    1. Support Hot/Cold/Rest/Rinse/Repeat protocol.
    2. Provide a space for bather participants to warm to room temperature before entering sauna (or other thermal experience) and without going outside in to cold weather.
    3. Showers: 
      1. Immediately adjacent to the sauna for cooling down and rinsing off sweat. 
      2. Sufficient count that bather participants will not need to wait.
    4. Rest:
      1. A comfortable area for bather participants to rest between rounds in the hot space.
    5. Optional:
      1. Cold Plunge

 

Baseline Usage Protocol:

  1. Altitude: Sea Level.
  2. Sauna Temperature: 85°c (average over time)
    1. Feet: 70°c ± 2°c
  3. Steam: 
    1. At 3, 7 and 11 minutes in to round.
    2. 330 ml each?
  4. Basic Timing:
    1. Rest, pre-protocol measurements and evaluation.
    2. Shower with soap.
    3. 15 minutes in sauna hot room.
    4. 20 minutes rest / cooldown:
      1. Option A: 
        1. Cool shower: 5 minutes
        2. Rest: 15 minutes
      2. Option B:
        1. Tepid Shower: 3 minutes
        2. Cold Plunge 5 minutes @ 18°c
        3. Rest
      3. Option C:
        1. Tepid Shower: 3 minutes
        2. Cold Plunge 3 minutes @ 10°c
        3. Rest
    5. Repeat for a total of 3 rounds
  5. Bather Spacing: At least 15cm between shoulders. 
  6. Attire: 
    1. Nude preferred
    2. Swimsuit (cover as little skin as possible)




 

Deviation is good.

While many or most studies should likely use the standard sauna and baseline protocol, studies that deviate from this are very valuable, particularly once the standard sauna and baseline protocol have been well studied.

It is critical that the differences between the standard sauna / baseline protocol and those used for the study be clearly documented for each element above as each can have an effect on outcome.

FWIW, a well designed larger sauna will likely have little effect on results while a smaller sauna is likely to have a measurable negative effect. There appear to be two inflection points with saunas for both enjoyment and health benefits with one being this size and another at about 180x180x230cm sauna.

 

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. 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?

Additional terminology and thermal taxonomy: https://localmile.org/thermal/

 

Notes on Sauna Design – Why This Design:

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.

 

Revisions:

2025.07.31 – First Draft