The humidity-sensing fan uses a sophisticated humidity sensor that responds to:(a)rapid to moderate(user-adjustable)increases in humidity or(b)humidity above a user-adjustable set-point(50%-100%relative humidity). The humidity sensor may occasionally turn the fan ON when environmental conditions change. If the fan continuously responds to changing environmental conditions,“H”(means“humidity”)adjustment may be required. This figure is factory-set for about 75% RH. Please see operation section in installation manual for more information.