Ventilation

There are two main ventilation methods we will talk about: Natural and Mechanical.

Natural ventilation

As the name suggests, relies on natural airflow for the air exchange.  This method is best suited for small-to-average-size saunas and all woodburning units.

There should be a vent underneath, or very near, the heater for fresh air intake. The heater pushes hot air up creating a vacuum underneath it that sucks fresh air in. There should be a high vent in the opposite wall or corner from the heater, where the air is allowed to escape. This vent should be 6"-18" down from the ceiling. In larger saunas (2) intake vents in opposite walls and (2) exhaust vents on opposite walls may be required.

Mechanical ventilation

Relies upon machines to, either, introduce air into the room or remove it. Fresh air can be blown in above the heater or near ceiling to mix in with hot air rising from heater, or air can be sucked out the bottom of the room across the room from the heater. If air is sucked out then fresh air intake should be above the heater (or under heater as well).

The following is from a Finnish Newspaper Article and really refers to mechanical air exchange:

According to the latest research by Valtion Teknillinen Tutkimuskeskus and Reijo Perala of Saunatec in Finland as published in the 01/00 Helsingin Sanomat of Helsinki, Finland, the intake vent for air into a electric sauna room should be located over the stove at about 2/3'rds up the wall (20 in. above stove). The out vent should be installed down low, like underneath the benches; the gap underneath the Sauna door most often is adequate for this purpose. The traditional method of venting has been to take the air in down below, underneath the stove, and let it out near the ceiling. This type of ventilation -underneath the stove- only works well when the unit is wood burning and requires fresh oxygen for the fire pit. The out vent for the room should always be down low for heat rises and vent up high would only let excessive amounts of heat to escape. In larger sauna rooms the air circulation should be aided mechanically and can be easily accomplished like explained next. The in vent is in the wall above the heater mixing cool fresh air with the hot air rising from the stove; The out vent is located underneath the bench(es) on the far wall; A duct is run from the out vent to above the sauna room and attached to a simple bathroom exhaust fan (preferably a quiet one). The air is then vented from the fan to the outside or to a indoor room where possible humidity and condensation pose no threat (rec. room etc.). The fan sucking the air out of the sauna room forces air circulation and pulls the hot air from the ceiling level lower for a smoother and more even bath. In the next table I am listing the temperature ranges and differences with the wrong and the right way of ventilating a sauna room.