The basic layout (electric heater)
- Fresh air in low on the wall near or under the heater, so cold air is warmed by the heater before it reaches you. Some makers place it above the heater instead: follow your heater's manual.
- Exhaust out as far from the intake as possible: low on the opposite wall (often under the lower bench) or through a duct that collects air from low down and leads it up and out.
- Air changes: heater makers usually recommend that the air changes about six times an hour. In the Saunoka heat model that ventilation costs a few hundred watts at 80 °C, which is why oversized vents slow the heat-up.
- A gap under the door often serves as part of the intake.
Wood-burning stoves
A wood stove draws its combustion air from the room, so it needs a steady supply of fresh air near the floor by the stove. The flue itself pulls air out while the fire burns. Many wood saunas get by with an intake low near the stove and a small exhaust vent that can be closed after heating.
Common mistakes
- Exhaust right above the heater: the hottest air leaves first and the room never feels even.
- No exhaust at all: stale, humid air, a stuffy feeling and moisture problems in the walls.
- Vents far too big: slow heat-up and higher running cost.
- Blocking vents to save energy: don't; carbon dioxide and humidity build up, and with wood stoves combustion air runs short.
Indoor saunas and the rest of the house
The exhaust should lead outside or into a room that is ventilated well (a bathroom with an extractor fan), never into a closed space or between walls. In basements, check that the house's own ventilation can take the warm, moist air.