Good ventilation in a sauna is critical for a number of reasons including maintaining safe CO2 levels, exhausting VOCs and clearing out humidity after a sauna session to reduce mold and bacteria growth. The recommended rate is 6 ACH.
Traditional ventilation is via convection with a supply vent at the floor (or a 4″ gap at the bottom of the door) and an exhaust vent at the top of an opposite wall or ceiling. So long as there is not too much static pressure this works moderately well. A newer option is to have a powered exhaust vent below the benches and then place the fresh air supply above the heater on the opposite wall. This works better both in terms of maintaining low CO2 levels for bathers and maintaining less of a temp difference from head to toe.
In North America it has become popular to have a fresh air supply vent at the floor and then a convection exhaust vent below the benches (typically this vent is about 2′ above the floor though may be as high as 4′ (in a 7-8′ high sauna).
I look at this and have two immediate thoughts; 1) There is nothing to induce adequate airflow out of the exhaust and 2) even if there is airflow then the bulk of fresh cold air will simply flow directly across the floor and up to the vent without benefiting bathers 7′ above.
Am I missing something? Is there a practical way that this can work without a mechanical blower?
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