Ventilation Design for Saunas

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.

  • Hot air rises (we all know that). A heat difference of 194°F reduces the weight of air by about 20%. This produces a considerable lifting force.
  • Rising air creates a convection of 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.
  • The ideal goal is to have 6 complete air exchanges each hour.
  • The low vent should be located close to the heater between the floor and 9” off floor. Another option is to under cut the door by up to 1” to create the low vent.
  • The high vent is where the argument comes in as to the best location: some like to have it in the ceiling others on the wall down 6” from ceiling and others just below the top bench. Which ever you decide on this vent must be operable and the best solution for this is to have it constructed out of wood. The outlet vent should be somewhere in the range of 20-30 square inches. You can close down vents to reduce the airflow but you can’t open vents that aren’t there to increase airflow. Finding the right ventilation pattern is more of an art form than an exact science.
  • Headaches and dizziness in the sauna can be a sign of too little oxygen. Watch for symptoms.
  • 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 often produce more heat than needed and don’t have precision controls. Design more ventilation into wood stove saunas than in electric heated 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 sauna produces much less moisture than a home shower). 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 be hot in a sauna.