The TK-400 universal twinning/paralleling kit is designed to allow a single thermostat to control two separate HVAC units. The TK-400 can also be expanded to control a total of four HVAC units. The device can be used on common or separate ducted systems with single-stage, multistage and heat pump equipment. Only standard 18-gauge thermostat wire is required. Thermostats and HVAC units can be located up to 300 feet from the TK-400 panel. When HVAC units share a common return and supply duct, backdraft dampers should be installed and thermostat fan operation must be set for electric.

Jackson Systems LLC, 5418 Elmwood Ave., Indianapolis, IN 46203-6025; (888) 652-9663; fax (317) 227-1034; www.jacksonsystems.com.