Honeywell THM5421R1021 IAQ Equipment Interface Module Four sensor inputs for wired sensors or dry contact devices Three sets of IAQ contacts to control humidification, dehumidification, and ventilation Used with all versions of Prestige IAQ Thermostats and the New RedLINK VisionPRO Thermostats Four sensor inputs for wired sensors or dry contact devices Three sets of IAQ contacts to control humidification, dehumidification and ventilation Used with all versions of Prestige IAQ Thermostats and the New Relink VisionPRO Thermostats