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Prevent Mold with the DewStop Bathroom Fan Switch

Updated: Jan. 11, 2023

Keep your bathroom (and house) fresh and dry without wasting energy

bathroom fan switchFamily Handyman
Control bathroom humidity more efficiently with a new type of humidistat switch that turns an exhaust fan on and off in response to changing humidity levels.

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Remove the old bathroom fan switch

Photo 1: Replace your bathroom fan switch

Follow the instructions included with the DewStop switch. Make sure the Power is off before you touch any wires in the box.

Photo 2: Installed bathroom fan switch

The new switch fits in the same spot as the old switch. You may have to buy a new cover plate, though.

If you just turn your bath fan on when you start a shower and off when you leave the room, it doesn’t run long enough to remove excess humidity. If you leave the fan running too long, you’ll waste energy.

A new fan control switch called DewStop solves both problems. It calculates when condensation will occur and turns the fan on and off automatically to keep the humidity at an acceptable level. This computerized switch is a vast improvement over the humidistats that have been around for years. You simply replace the switch or timer that controls the fan with the DewStop switch. It’s available online at or from online retailers. If you’re replacing a double switch that controls the fan and the light, order the version that includes a light switch.


Turn off the power at the circuit breaker box before removing the old switch.

Required Tools for this bathroom fan switch project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • 4-in-1 screwdriver
  • Electrical tape
  • Non-contact voltage tester
  • Wire stripper/cutter

Required Materials for this bathroom fan switch project

Avoid last-minute shopping trips by having all your materials ready ahead of time. Here’s a list.

  • Fan Control
  • Wire nuts