Sauna ventilation
The short answer
A sauna needs fresh air in and moist air out. Harvia says the air in a sauna with an electric heater should change six times an hour. With natural ventilation, the inlet goes below or beside the heater (50 to 100 mm across) and the outlet low down on the far side, twice the size. Infrared cabins usually have vents built in.
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Why it matters
- Better heat. Fresh air keeps the heat from feeling stuffy and helps the steam feel soft rather than harsh.
- Even temperature, with less difference between your head and your feet.
- Drying out. Moist air has to leave after every session, or the wood stays damp and goes musty.
Electric heaters
| System | Fresh air in | Air out |
|---|---|---|
| Natural (gravity) | Below or beside the heater, 50 to 100 mm diameter | Near the floor, as far from the heater as possible, twice the inlet diameter |
| Mechanical | High up, kept away from any separate temperature sensor | As the system designer specifies |
From Harvia's ventilation guidance. Some saunas also have a drying vent high up: keep it closed while heating and bathing, and open it afterwards, or just leave the door open.
Wood-burning stoves
- Natural ventilation: fresh air in close to the floor near the stove, and out as far from the stove as possible near the roof, mainly to clear moisture after bathing.
- Mechanical ventilation: fresh air in about 500 mm above the stove, and out close to the floor, for example under the benches.
The stove also draws air to burn, so never block its air supply.
Infrared cabins
Infrared cabins run cooler, have no steam, and usually come with small vents built into the roof or walls. They don't normally need ductwork. Leave the clearances around the cabin that the maker gives, so air can move around it.
The room around it
- Fresh air into the room, from a window, trickle vent or air brick.
- Extraction where moist air comes out. If the sauna vents into a washroom, Harvia says there must be at least a 100 mm gap under the sauna door and mechanical extraction in the washroom.
- No sealed cupboards. A sauna in a closed space with no air supply will struggle to heat well and to dry out.
Common questions
Does a sauna need ventilation?
Yes. Fresh air makes the heat feel better and drier, stops the air going stale, and helps the sauna dry out afterwards. Harvia says the air in a sauna with an electric heater should change six times an hour.
Where should the vents be in a sauna?
For an electric heater with natural ventilation, Harvia puts the fresh air inlet below or beside the heater and the outlet low down, as far from the heater as possible. Mechanical systems and wood-burning stoves use different layouts, so follow your heater's manual.
Do infrared saunas need ventilation?
Infrared cabins usually come with built-in vents and need no extra ductwork. Leave the clearances around the cabin that the maker gives, and put it in a room that's ventilated itself.
Can I put a sauna in a room without a window?
Often, yes, but the room itself needs a supply of fresh air and a way for moist air to leave. If the sauna vents into a washroom, Harvia says mechanical extraction is mandatory there.
How big should sauna vents be?
Harvia gives a fresh air inlet of 50 to 100 mm in diameter for natural ventilation with an electric heater, and an exhaust twice the diameter of the inlet.
Sources
More in installing
- Planning permission
- Electrical requirements
- Base and siting
- Delivery and assembly
- Bathroom, attic or garage
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