The twinning kit is designed to allow a single thermostat to control two separate HVAC units. It can also be expanded to control a total of four HVAC units. The twinning kit can be used on common or separate ducted systems with single-stage, multi-stage and heat pump equipment. Only standard 18-gauge thermostat wire is required. Thermostats and HVAC units can be located up to 300’ from the twinning kit panel.