Check the listing for details. 4655 Manual Whole-House Duct or Wall Mounted Humidifier Control Humidistat. Color: White, Condition: New. Listed at 14.79 USD. 4655 Manual Digital Control Humidistat Control Switch for Whole-House Duct or Wall Mounted Humidifier Control Humidistat 24VAC（White） Product Description Design for---Replace series:400/500/600/700 Evaporative Humidifiers, and 800 Steam Humidifier. Necessity device---This manual humidistat model 4655 can't sense outside, so you play the part in telling the humidistat what the outside temp is by dadjusting the knob. And the knob value you turn to is the relative humidity manual setting, which is a max rh value that prevents inside condensation, so choose either the max rh value for the outside temp or a lower rh value. Good replacement unit---When the humidifier no longer works or its performance deteriorates, and the control switch starts to change color due to long-term use, replacing it is a reasonable choice. The white fashionable modern appearance undoubtedly adds an elegant and minimalist touch to the home environment. Installation location---Please choose to install pipes near HVAC equipment or install them on walls in your living space, at least 6 inches upstream of the humidifier(If conditions permit). Easy to install---Pop off your old humidistat and make sure it is a 2 wire system, after removing old unit just wire this up, no need to worry about polarity.