Never run wire again on retrofit applications, Up to 4 Heat / 2 Cool, 3 Wire communicating design, Mount directly on wall or horizontal outlet box using mounting plate to prevent electrical shorts, New Style Look, Integral switches control system and fan switching, The TH9421U touch screen universal programmable thermostat provides electronic control of 24 Vac heating and cooling systems of 750 mV heating systems in addition to humidification dehumidification and ventilation, SKU: HMREX796