Humidity Module The W351 is an electronic humidity control with SPDT output relay and LED indication and requires a 24VAC power source. The W351 covers a range of 0 to 95% RH and has adjustments for setpoint, differential and mode (humidification or dehumidification). The S351 Stage, D351 Display and Y350 Power modules can be used with the W351. Humidity Module 2.4" x 2.4" x 5"