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There are two important things to understand about humidity sensing fans. First, the best models sense the change in humidity, not the humidity level itself, so climates that are naturally more humid will not trigger the fans to operate unless over-ridden by the occupant. And second, sensitivity levels and after-run times can be personally set by the home’s occupants.

Installing a wall timer switch allows the fan to remain on long enough to remove the excess moisture without having to return to switch it off.

Location of the bathroom fan is also a critical factor in ensuring proper performance. The first choice should be over the shower. If this is possible, select a fan UL-listed for tub or shower installation.

Where that is not practical, one should visualize a line from the bottom of the bathroom door and the heating/ cooling register (which are the exhaust fan’s air supplies) to the ventilator. Make certain that that line passes through the steam cloud generated by the shower. Air flowing through the room along that line will capture the excess moisture from the shower.

Since intermittent contaminants are produced in high concentrations, a high ventilation rate is required to keep them from dispersing throughout the house. This explains the relatively high airflow rate of typical intermittent kitchen and bathroom ventilation.