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Electric Heated Sauna Ventilation Setup

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Air Mixing and ventilation setup with an electric heated sauna -Part One

By Malcolm Reese   April 2024

Recap of Sauna Times February Post

The SaunaTimes February Post reviewed the findings from the 1992 Finnish Ventilation Study and provided the necessary information needed to set up the correct ventilation system in an Electric Heated Finnish Sauna. Three phases of the Study were discussed in the Sauna Times February Post:  Air Mixing Experiments, Temperature Experiments, and Air Condition. As a follow-up to that article, we thought we should profile an actual North American Electric Heated Sauna utilizing the findings of that Study and Post.. 

Scope of this Post (Part One) 

We realized I had accumulated several months of temperature data on various zones within my Sauna while utilizing the Study’s T4/P2 ventilation Opening combination. Some additional data was needed to fill in some holes in my Sauna profile to address this particular behavior seen in front of the Stove. With the expansion of the scope of the proposed second Sauna Times Post on this topic, it became apparent the new Post may need to be presented in two or three separate parts: one for each of the three areas mentioned above that were researched by the 1992 Finnish Study and written in the Sauna Times February Post. I will address the Air Mixing Experiments section of the Study here. 

To effectively utilize data taken from a Sauna you need to establish the parameters of the actual “Test Sauna”. Sometimes this important detail is omitted when pronouncements are made to the “Sauna World”. 

My Test Sauna’s Equipment, Dimensions and Setup 

The test facility is a Thermory No. 63 Barrel Sauna. The interior diameter is 7 feet. The two benches are about 6 1/2 feet in length and 23 inches in width. The benches are 20 inches above the Duckboard floor. Allowing for the Thermal Glass Door, the “effective” volume of the Sauna is about 280 Cubic Feet. The Sauna is heated by a HUUM 9 Kw DROP electric stove with a UKU Local controller. The Drop, a Net type heater, contains about 120 pounds of stone thermal mass. It’s wired to a 230-volt 50-amp single-phase circuit.   I used the UKU controller “Ramping” Heating cycle mode to heat up and shut off the heating cycle during the Sessions. 

The inlet Air Flow is 35 CFM for the “Test Sauna”, which is equivalent to about 8 Sauna volume changes per hour. I measured the flow rate at the Inlet Air opening (T4), whereas the Finnish study measured it at the exhaust openings (P2). They had a leakproof Sauna. Mine may still have a few volunteer leakers in it, but they don’t affect the “Test Sauna” ventilation system setup. I felt that measuring the flow rate of the fresh air coming into the Sauna was a more descriptive constant for controlling ventilation than using the exhaust value as a control. In the U.S. a 6 to 8 air volume change per hour is recommended for Finnish Sauna ventilation. To provide this, one 4-inch Exhaust vent was installed under each Bench, including an in-line variable speed Fan for each location. The accompanying photos show the inlet and outlet of the “Test Sauna”. 

The original 1992 Study showed that the placement of the Inlet Air Opening needed to be halfway between the top of the Stove and the Ceiling (T4 in both previous studies). The Exhaust Opening(s) needed to be located under the Bench as far away from the Heater as possible and as high up from the floor as possible (P2 in the studies). The photo below shows the inside of the “Test Sauna” near the rear wall (also the stove location). Several things are important here to explain the functioning of this new profile Study. The Inlet Cold Air Opening is located halfway between the ceiling and top of the stove (T4 in the studies). My Inlet Air Opening (T4) is 26” down from the Ceiling and 26” above the top of the Stove. In the original 1992 Study, they used a 160 mm diameter inlet (6.3 inches).  I used a 6-inch diameter opening. The 160 mm opening, used by the original Study, is about 31.1 square inches.  My 6” diameter opening provides 28.3 square inches (9% less than the original study.)

Temperature Measurement Setup

The Dish-Temps Tree (see photo) contains four temperature-measuring instruments to record the temperatures at various positions in the Sauna zones being studied. During the experiment, the Tree is pointed towards the Stove to obtain the air temperature surrounding the Dish-Temps. These four instruments were calibrated to NSI standards. Three other Temperature measuring devices that were also used can be seen in the photo, two are on the floor under the bench, and one is on top of the bench. Their accuracy was checked against the calibrated instruments and was within a 1-degree reading. These were used to record temperature data on the benches and the floor. A second, shorter Dish-Temp Tree, was also used to measure temperatures at some zones away from the front edges of the Benches using these same four Dish-Temp instruments. The longer Tree would not fit between the curved Ceiling and Bench height of the Barrel Sauna.

The Dish-Temp is a Device that is used to measure the Sanitizing Temperature (165 degrees F) in Commercial Dishwashers. It is designed to be placed in the rack of a Restaurant’s dishwasher along with the other dishes. It then records the highest temperature it sees and displays the current temperature in a high-temperature and water-immersed environment. They are rated at 90 degrees Celius, but I have heated them up to 99 degrees C without any apparent harm. I ran a few trials and found they performed better when they were exposed on all sides to the temperature environment you were subjecting them to, similar to the condition they see in their normal application.

Containing the Heat 

The photo below shows the two external 4-inch exhaust fan vents underneath each bench (P2 in both studies) located on each side of the door I used in this Study. Each fan has variable speed controls.  In the upper left corner of the Sauna, you can see a third vent, above the robe/towel hooks, that is only opened after completing your Sauna session to help air out the Sauna. If you look at the doorway, you will see a very important modification I added to my Sauna build: a bath sheet. The sheet is suspended from the inside of the doorframe. I noticed each time I entered or exited the Sauna, the temperature would drop a few degrees in the Sauna. When the Bath Sheet was placed behind the door, a hot air dam effect was created, resulting in the heat being held in as I entered or exited the Sauna. 

I found that the biggest negative effect of any ventilation system, confirming the earlier 1992 Study, was that air leaks are a very bad thing to have in your Electric Heated Sauna. All or as many air leaks as possible need to be sealed, otherwise the efficiency of the ventilation system and the presence of the Finnish Sauna characteristics you seek goes down drastically. The Sauna does not need to breathe (leak) during operation. It breathes when you leave the Door open and open the vents to allow it to cool down after your Sauna session is over. The only “Breathing point” and “Exhaling point” for a Sauna session should be the T4 and P2 openings. My Door frame was the biggest leak source for my Sauna, and it took a while to seal all of them. Sealing the Door air leaks near the Exhaust vents resulted in an immediate increase in the airflow rate of 22% at the Inlet Air Opening (T4) above the Stove, showing the negative effects of air leaks on a Sauna’s ventilation system and its performance.

Exhaust Vents for electric sauna ventilation

The photo below shows the placement of one of the Exhaust vents Slider under the Benches inside the Sauna. It was placed in accordance with what the original 1992 Study stated as the P2 (Fan assisted location), located as far above the Floor and as close to the underside of the Bench as possible with a screened slider to close or dampen it. The results of just placing the vent under the Bench was found to be more important than its height above the Floor. The flow dynamics established by the T4/P2 setup address that. Initially, I was going to have the fans mounted inside the Sauna, but due to the low-temperature tolerance of the fan’s internal assemblies and the potential noise, I ended up placing them outside of the Sauna. This has worked out quite well.

The second photo below shows the exterior setup for the variable speed in-line Fans used to assist the exhaust function of the ventilation flow pattern of the Electric Heated Sauna at the P2 location. I placed a 4-inch coupling over the 4-inch diameter vent opening cut in the Sauna wall, with a gasket lining between the Sauna Wall and the coupling. This was intended to help dampen the vibration coming from the Fans. The second component with the metal bands is a sound-dampening sleeve that the fan manufacturer recommended. Finally, the last component is the 4-inch variable speed in-line Fan. 

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The last photo shows the homemade “holder” used for the Dish-Temp devices.

This completes the description of the “Test Sauna” setup.  The above information also shows what can be done to modify a currently active Sauna to take advantage of the 1992 Finnish Ventilation Study findings and the expanded information given in the Sauna Times February Post.


The Sauna Times February Post was intended to evaluate and expand the knowledge of the “Translated 1992 Study”. The first portion of the 1992 Ventilation Study looked at the Air Mixing characteristic of an Electric Heated Finnish Sauna. One of the findings was that there was a very strong Hot Air to Cold Air mixing activity in the area above the stones on top of the stove and the Cold Air Inlet Opening, the T4 location above the Stove. They noted that a subdued mixing action occurred beside and below the Stove when the T4 opening was used with the P2 (Fan assisted) Exhaust Outlet Opening. The parameter in this Study that’s used to determine the air mixing component is the Temperature Profile Data shown in the Table below and the graph showing the actual temperature profile of the Zones for this study. This profile includes seven zones in and around the Stove and Ceiling and the areas away from the Stove at various distances along the rear wall and the mid portion of the Benches. Seven separate Temperature zones were selected, and their average recorded data is presented in the Table. 

The six (6) temperature positions of the Study extend vertically from the Floor to just below the Ceiling and are shown for each of the seven (7) zones in the Table.  These positions are the four (4) devices (positions 1-4) on the Dish-Temp Tree and the other temperature measuring devices that were located on the Benches and the Floor (positions 5 – 6). The first photo you saw in this Post shows some of those components. The seven columns in the table represent the zone placement areas within the Sauna. 

Temperature Measurements in degrees Celsius 

Right Side (facing door)Left Side (facing door)
Temp. DeviceMid Bench (from edge to wall)Front Edge Bench7” Left of CenterCenter of Sauna in Front of Stove7” Right of CenterFront Edge BenchMid Bench (from edge to wall)
Pos. 175-76” above floor; mid-bench 70”86909193*7” below ceiling929286
Pos. 2Center of Air Inlet ; head height for bench; 59” 81828384838282
Pos. 3Top rail of backrest; 45” 80858691878681
Pos. 4Top of Stones34.5” 78929599989280
Pos. 5Bench; 20” 64686770697069
Pos. 6Floor; 0”50545355515357
Distance from Back Wall9”11”18.5”20”18.5”11”9”
Distance from side of Stove21”7”6”7”6”7”21”

Each row in the Table is a different distance from the floor, as noted in the first column, for each of the seven zones. The last two Rows in the Table show how far away each Tree was from the back wall and the side of the Stove during the trial. For example, the Tree used for measuring both Mid-Bench zones was attached to the Ceiling directly above the mid-point of the width of each Bench and located 9 inches from the back wall and 21 inches from the side of the stove (see the last two rows of the table). The height of the Temperature measuring device from the floor for each position (1–6) is shown in the Table.  

The graph above shows the temperature for each zone at each temperature measurement height. The two zone columns in the table for the ‘Front Edge of Bench’, the ‘Mid-Bench’, and the ‘7” from Center’ Tree locations were combined by averaging them together. The 1992 Study stated that there was a very strong flow pattern effect going on concerning the Hot Air Sauna stream coming up from the top of the stove and its turbulent mixing with the Cold Inlet Air coming in from the T4 opening. This was unique to the T4/P2 ventilation opening combination. This flow dynamic is shown in the graph as beginning at the 20” level (Bench Pos, 5) for the zones shown in the graph as the top three curves.

The 35” level (just above the stones Pos.4} is where the hot air from the stove raises the Sauna Air Stream temperature to its highest level. The Sauna Air stream’s rapid mixing pattern with the Cold Air coming in from the Inlet Air opening (T4) starts just past this 20” level (Pos. 4). The region in the graph where the three top curves drop in temperature at the 45” level (Top Rail of Backrest Pos.3) and at the 59” level (Centerline of Inlet Air Opening Pos.2) above the floor, is where this unique turbulent Air Stream mixing occurs that the 1992 Study was talking about. After passing the 59” level, all four curves are stabilized and rise in temperature to their respective high points and start to flow along the Ceiling, pulled by the mechanical forces of the Fans in the Exhaust vents at the P2 openings. The Mid-Bench zones did not have a drop in temperature as seen in the Table and the 5 zones represented by the three top curves in the Graph. Its flow pattern was outside of the region impacted by the Hot Air stream coming up from the Stove and the Cold Air coming in from the T4 opening.

Discussion of Findings

The first trials were run directly in front of the Stove.  At this zone, the cooler Sauna Air from the Floor and the Hot Air coming up from the Stove are mixed with the fresh Cold Air coming in from the Inlet Cold Air Opening at T4. The pattern seen at this zone shows a temperature increase as the distance above the floor increases, peaking at Position 4, 34.5 inches above the floor slightly above the top of the stones. This pattern was also seen to a lesser degree in the two zones 7 inches to each side of Center, and even at the zones at the front edge of the bench. As you go up the Tree to the next position (Position 3) there is a large drop in temperature at that height for all five of these zones. At Position 2 on the tree a temperature drop also occurs but at a smaller increment for these zones too. Finally, the temperature increases again at Position 1, 7 inches from the Ceiling.

This temperature pattern is a common characteristic shared by these five sauna zones. The unique temperature changes shown reflect the strong interaction that takes place with the mixing of the three different Air Streams caused by the T4/P2 (fan-assisted) ventilation combination. This confirms what the original 1992 Finnish Study found. At the first and last zones in the Sauna, the mid-bench columns, we find the more typical stratification patterns you expect as the normal heat flow profile produced by an Electric Stove.  None of the other Inlet Air Openings (T1- 3) or Exhaust Openings (P1 and 3) combinations that were tried in the 1992 Finnish Study could produce this Ventilation flow pattern necessary to create the Characteristics you seek in a Finnish Electric Heated Sauna. At Position 1, just below the ceiling, the mixing has stopped and the rising hot air elevates the temperature in this area. The Center Sauna zone had the highest Ceiling temperature found for this phase of the study.


The scope of this Study was expanded to include 6 other Sauna zones because of the important flow pattern that was observed in the Center zone directly in front of the stove. The data shows that this flow pattern is critical to effectively drive the Ventilation system necessary for an Electric Heated Finnish Sauna. The key points of the conclusion are:

  1. The two zones on both sides (7 inches from the Center) demonstrated a Hot Air to Cold Air mixing pattern, with resulting Temperature changes, similar the Center zone, but to a lesser intensity. This was due to being further away from the Inlet Air Opening (T4) and the Hot Air stream coming up from the Stove.
  2. Similarly, the two zones at the front edge of the bench exhibit the same pattern, but the high temperature at the stone height is a few degrees less than the high temperature seen at the three zones nearest the Center zone.
  3. Finally, the two zones furthest away from the Inlet Opening (T4) and away from the Stove, located at the Bench’s mid-point, showed the more common heat temperature stratification pattern normally seen in a Sauna. 

The next Sauna Times Ventilation Post on this topic will examine the remaining two characteristics, “Temperature Experiments” and “Air Condition”, associated with the T4/ P2 Ventilation Opening combination from the 1992 Finnish Study findings. 

ACKNOWLEDGEMENTS – I want to thank Glenn Auerbach for his patience and willingness to showcase this Post through the SaunaTimes forum and John Williams for his extensive Editorial and Technical review of the article for me.

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