Your commercial or residential sauna design needs to include ventilation.

Commercial and residential sauna designs deal with oxygen levels, heat circulation and comfort. All of this is determined by the ventilation pattern. The purpose of ventilation is to maintain oxygen levels and circulate (not eliminate) the heat.

sauna design picture

BACKGROUND INFORMATION

Hot air rises (we all know that). A heat difference of 100* C reduces the weight of air by about 20%. This produces a considerable lifting force. As Dorothy in the Wizard of Oz found out it is enough force to float people in balloons and cause destructive tornados.
Rising air creates a convection current in a sauna. As the air rises it spreads along the ceiling and flows down the walls as it cools. It is pulled along the floor to replace the new air that is rising from the stove. This pattern naturally circulates air in the room.
There is a “piston effect” that happens when water is poured on the hot rocks. The steam quickly expands, pushing air from the sauna. As the air cools and shrinks it pulls some outside air back in. This can help exchange the air (oxygen) in the room.I taught science for years and one of my favorite demonstrations showed this principle by creating a pop can implosion. It’s simple, quick and impressive. If you are interested, it is explained at the bottom of this page (kids love it and you may get a kick out of it as well).

I’ve seen it written that your goal is to have 6 complete air exchanges each hour. Do what you will with that number, I don’t think we need to get so precise.

WHAT SHOULD YOUR VENTILATION PATTERN BE?

In a residential sauna design the idea is to circulate air not just exchanging it. Having an intake at floor level and exhaust in the ceiling is not the best pattern for circulation.
Lowering the exhaust vent to a level below the upper bench will cause the incoming air to rise and then come back down to he exhaust vent. This effectively mixes the air.
To get any circulation at all the exhaust vent needs to be at least 14” higher than the intake vent. 28” is a good height difference between incoming and outgoing air.
The vents should be on opposite walls.
A common sauna design pattern is to have the incoming air enter either under the door or under the heater. The exhaust vent goes on the back wall under the upper bench. Leaving a 1”-2” gap between the door and the floor makes for an easy incoming vent.
In a residential sauna the exhaust vent (not the intake) dictates how much air is exchanged. Incoming and outgoing vents should have about the same total cross section. If there is a difference the exhaust should be the bigger of the two. Somewhere in the range of 30-48 square inches for each vent works in most saunas. This is a 3” x 10” to 4” x 12” vent.

ATA (also think about)
Headaches and dizziness in the sauna can be a sign of too little oxygen. Watch for symptoms.
You can close down vents to reduce the airflow but you can’t open vents that are not there to increase airflow. Finding the right ventilation pattern is more of an art form than an exact science. Your best bet is to put more ventilation in your sauna design than you expect to use. This gives you the flexibility to experiment and find the right formula.
Some sauna designs have inherent “cold spots” such as corners. Try to visualize the airflow pattern and eliminate problems though vent location.
In commercial and residential sauna designs that use wood burning or gas heaters there should be an external air intake. This is for the heater and is separate from the ventilation used to circulate breathing air and heat.
Wood stoves can often produce more heat than needed and don’t have precision controls. Electric heaters typically don’t produce a lot of excess heat. Design more ventilation into wood stove saunas than in electric heater saunas.
The “löyly” is not a heavy, wet steam. The exhaust of an indoor sauna can usually be vented back into the house without moisture damage. A commercial sauna, in continuous use should be vented to the outside. Even in some residential sauna designs, people will use a bathroom style electric vent fan to vent the moisture outside. This should only be used when you are finished using the sauna for the day.
Air vents (especially the exhaust) need to be adjustable. It’s best if the control mechanism is wood. There is a good chance that anything metal will eventually corrode in a sauna.

POP CAN IMPLOSION
***Use a heavy glove, towel or other protection to hold the can once it gets hot.*** WHAT YOU NEED
A heavy glove or other heat protection.
1 empty pop can (get lots more if there are kids around because they will force you to repeat it again and again).
A little bit of water
A stove, or hot plate
A large pan (a large rectangular baking pan works well) with about 2” of cold water in the bottom
WHAT YOU DO Put a small amount of water (a teaspoon or so) in the pop can. You are better off with too little water instead of too much. Put the can on the stove and wait until you see steam coming out and you can hear the water boiling. Using the glove or other protection, quickly take the can off the stove and put it top down into the cold water in the baking dish.
The air inside will shrink faster than the can will be able to draw up water from the baking pan. The can will implode, sometimes loudly and quickly. Also notice that you can pour out much more water after it implodes than the small amount you put in at the beginning.

One of the most important considerations for commercial and residential sauna designs is the ventilation pattern. Proper ventilation helps circulate the heat evenly and insures that there is plenty of oxygen to breath.

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