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Sauna Ventilation, Done Right
Ventilation is the unsung hero of good sauna performance and longevity. In a previous post, we discussed why this component of the sauna build is critical to success. A sauna with good airflow feels alive: the heat is even from floor to ceiling, the air stays breathable even at high temps, and the room dries out fast once you're done.
Here's the primary system we build into our Driftwood saunas, and the reasoning behind it.
Big Picture: One Intake, Two Exhausts
Every sauna needs a path for fresh air to enter and for stale air to leave. We do this with three vents, not two – something we find has a dramatic effect on performance:
Intake — low, positioned under or beside the heater
Lower exhaust — on the opposite wall, typically positioned below the upper bench
Upper exhaust — near the ceiling, on the same wall as the lower exhaust
Most of the "how to vent a sauna" advice out there stops at a single intake/exhaust pair. This is also what’s most common in sauna kits (if they consider ventilation at all). That ‘works’, but I find that setup to be suboptimal compared to the dual exhaust method. Running two exhausts at different heights lets us separate the two jobs that we task the exhaust vents with and have optimal setups for both: one is keeping the room hot and oxygen rich during a session, and the other is clearing heat and steam out fast after one.
Intake Placement and Theory
Cold air is dense — it wants to sink. If you place your intake low and near the heater, incoming fresh air gets pulled directly into the heater's convection currents and pushed up and across the room as it warms. That's the engine that drives air circulation through the whole space. Locate the intake far from the heater and you lose that free convective push; you're relying on stray air movement instead of an intentionally designed current.
Low Exhaust Placement and Theory
This is the detail most people get backwards, and it's the one I'd call the most important (and frequently absent) piece of the whole system. Saunas will always naturally stratify — hot air collects at the ceiling, cooler air sits at the floor. That's normal and even desirable to a point (it creates differing temperature zones that can be leveraged when users have varying heat tolerances), but when uncontrolled it means your feet are in a completely different climate than your head. An exhaust placed high, up at the ceiling, will preferentially pull exclusively from that hot layer and reinforce the stratification. It's constantly bleeding off the room's hottest air, forcing the heater to keep replacing it, and leaving the lower half of the room relatively cool.
Placing the exhaust low — typically just under the upper bench — does the opposite. It draws air from mid-room height instead of skimming the ceiling, which pulls the whole air mass toward equilibrium instead of into two layers. The result is a noticeably flatter temperature gradient between the ceiling and upper and lower benches. This is the vent that stays open continuously; during preheat and your active session. You want to strive for the lower vent placement to be across the room (catty-corner is probably most ideal, but opposite wall definitely works) from the intake and heater. It is more important to have the lower vent catty-corner / opposite wall placed than the upper vent for sauna performance.
Upper Exhaust Placement and Theory
The vent up near the ceiling isn't there to manage comfort while you're sitting in the room — it's there for what happens the moment you're done. Once a session ends, you want to purge the room of both residual heat and the humidity load that a session dumps into the sauna room. The most extreme hot and moist air is sitting right at the ceiling where it naturally collects all session long. Opening the high exhaust gives that layer a direct path out, and the room clears in a fraction of the time it would take relying on the lower vent alone. This improves the longevity of your sauna as the extreme heat is purged far quicker post session than otherwise if you only rely on the lower vent for post session exhausting.
What This Actually Looks Like Behind the Walls
We run rigid or semi-rigid galvanized duct through the framing cavity from the vent location out to the exterior wall — cutting through top plates, blocking, and insulation as needed, and taping every joint before it disappears behind the vapor barrier and cladding. We often use dryer slim-fit hookups, as they allow us to cut partial notches in our framing top plates as opposed to completely severing them.
On the exterior side, the exhaust point varies by home / wall construction and what’s available nearby. We typically will send it through a rim joist, similar to a dryer vent, but on other occasions we’ve drilled large diameter holes through glass block windows when the exterior facade presents additional challenges. We think it’s important to avoid using PVC vents and components, as they are not normally rated for the temperatures that our saunas can achieve (200F+).
Inside, once the T&G wall cladding goes up, each vent gets trimmed out with a simple round cover — nothing fancy, just enough to finish the opening cleanly and let it disappear into the wall. These covers screw open and closed very easily / intuitively. The intake usually gets a wooden floor register type of cover that blends with the walls and cannot be accidentally shut.
Summary
We find the most effective ventilation setup to be composed of (at least) 3 vents – one intake and two exhausts. Place the intake under or beside the heater, and the exhausts in a high-low composition across the room from the heater.
Have questions about ventilation on your own build, or want to see how we'd lay this out for your space? Reach out — this is one of the details we don't cut corners on, and it will completely alter the performance of your sauna if done correctly vs improperly.
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