Lennox EIM, Residential Communicating Control System Equipment Interface Module The Equipment Interface Module (EIM) allows a Lennox Communicating Thermostat to be used with most noncommunicating HVAC systems. The EIM allows most conventional, non-communicating furnaces or air handlers (up to 3 stages heating and 2 stages cooling) to emulate a Lennox Communicating indoor unit (with reduced communication features). Contains all necessary relays and controls to emulate a Lennox Communicating indoor unit Module has two green LEDs One indicates status and aids in troubleshooting, a second LED indicates active RSBus communication Any system alerts/warnings are transmitted to the Lennox Communicating Thermostat Serial communications bus (RSBus), with less wiring than a conventional heating/cooling system, allows system communication Uses 4-wire, 18-gauge standard thermostat wiring for connection to the Lennox Communicating Thermostat Conventional thermostat wiring connects the EIM to the non-communicating indoor/outdoor unit equipment