How to Regulate Humidity in a Bathroom

Bathrooms are very wet environments, and this can cause damage to the interior finishes or lead to the possibility of mold growth over time. One important design consideration if building new or remodeling a bathroom is how to regulate this high humidity level.

The first step is to make sure you have a good bath ventilation fan. But even more important is to ensure that the fan is properly exhausted to the exterior of the the home and not just into an attic or plenum space. You may find it surprising how many bath exhaust fans simply expel the moist bathroom air into the attic above and not directly to the outside!

The next step is to add either a timer or a dehumidistat to the fan controls. A timer will engage the fan to run for a specified length of time and then shut itself off. The theory is that if the fan runs for twenty or thirty minutes after showering or bathing, the humidity level will return more or less to a normal level. Of course, this is a bit of a guessing game.

A dehumidistat takes humidity control one step further. It is a wall mounted device that actually measures the relative humidity of the bathroom air and directly engages with the fan switching. It will run the fan until the humidity reaches the desired pre-set level – which for most homes should be
around 40 or 45 percent.

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