Correct sauna ventilation is considered one of the most integral aspects of any sauna build. However, every Finn has a slightly differing opinion on what is the optimum ventilation set up. Of course, it depends on a number of factors, such as type and size of heater, shape and size of sauna room, bench height, sauna layout, whether there is an air gap under the door and so on.
Ideally, a simple ventilation set up would consist of: An air source under the heater which could be under the sauna door. Another under the sauna bench to help bring the heat down, and one in the ceiling as a heat dump.