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 dewstop.com 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.
1.) REPLACE YOUR FAN SWITCH WITH A "DEWSTOP" SWITCH
Follow the instructions included with the DewStop switch. Make sure the power is off before you touch any wires in the box.
2.) INSTALLED SWITCH
The new switch fits in the same spot as the old switch. You may have to buy a new cover plate, though.