Have you ever been into a sauna that is stale, stuffy, horrible smell, and you can wait to get out just within a few minutes of entry? Likely, you had entered a poorly design sauna with bad or no ventilation.
Convection Thermal Transfer
Sauna ventilation is not required for safety reasons, but it makes the sauna experience more comfortable. Most sauna heater manufacturer will state the ventilation requirements, as improper or insufficient air flow can impede heater operation.
Sauna design incorporates heat circulation and comfort through convective thermal transfer. As air gets heated from the sauna heater, hot air rises, spreading along the ceiling and flows down the walls as it cools. New heater air rising from the heater continues the effect, circulating air in the sauna naturally.
When you do the Löyly (pronounce as “Louu-lou”, which means envelope of heat and steam that surrounds you in the sauna as water is poured on the hot rocks), it creates a “piston effect” where the steam expands, pushing air from the sauna and pulls in new cool air as it shrinks. This movement assist the change of air in the sauna.
Ventilation Design
The concept of convection heat circulation is the basis of sauna ventilation design.
The sauna requires a low inlet vent, located near to the heater; a high outlet vent, located at the ceiling or wall, furthest location possible away from the heater.
The outlet vent is best construct with a manual open/close mechanism, to retain the heat (vent close) for a higher temperature sauna experience.
There are designs of the outlet vent below the top bench, allowing convention heat current to flow down the walls and out from the vent, controllable with the manual open/close vent.
Whichever design you decide on the vent, ventilation is an important aspect in sauna design. Having a stale stuffy sauna, which leads to headaches and dizziness, could be the cause of too little fresh air (oxygen).
Without proper air circulation, whether the sauna is in operation or not, will lead to mould and bacteria growth.