A:Answer The Honeywell TH9421C1004 thermostat connects with an Equipment Interface Module or EnviraZONE panel, to control temperature, humidification, dehumidification, and ventilation. In some systems, legacy wiring terminals are available. Legacy wiring terminals include; R, W, Y, G, and C. If legacy wiring terminals are available, a Honeywell Wi-Fi thermostat can be wired to those terminals to control the system. We recommend that you contact a Heating Ventilation and Zoning professional, for further consultation.