Depending on configuration, either on the apartment unit, single-family house or apartment building level. As the other commenter said, nowadays sauna in Finla

Depending on configuration, either on the apartment unit, single-family house or apartment building level. As the other commenter said, nowadays sauna in Finland is usually inside your house and the mechanized ventilation is connected to the overall ventilation system of your house. Hence the original article[1] explored the optimal positioning for mechanized air in/outlets in a sauna. The current Finnish building code incorporates the recommendations from this study (as document RT 91-11260). I guess you could apply the same principles to an electric sauna in a separate building. Just use two fans (one pulling, one pushing) instead of an AC system. Most often a separate sauna building in Finland however has a wood-fired stove, which doesn't need as much consideration for ventilation as an electric sauna. My understanding is that the wood-fired stove itself creates a strong continuous draft which takes care of ventilation in the sauna room (pulling fresh air from outside through the stove and by combustion into the chimney). [1]: https://publications.vtt.fi/pdf/tiedotteet/1992/T1431.pdf https://publications.vtt.fi/pdf/tiedotteet/1992/T1431.pdf