The MRCOOL PHK20H ProDirect Series Heat Kit 20kW is an electric auxiliary heating accessory designed for compatible MRCOOL ProDirect Series air handlers and split-system HVAC equipment. It works by energizing high-capacity electric heating elements when additional heat is required, providing supplemental warmth during cold weather or heat pump defrost cycles. https://www.partshnc.com/mrcool-prodirect-series-20kw-heat-kit-phk20h