The MRCOOL UHK05 Universal R-454B Air Handler Supplemental Heat Kit is a 5kW electric heating accessory designed to provide additional warmth for compatible MRCOOL air handlers using R-454B refrigerant systems. It works by generating electric heat when the heat pump requires extra heating capacity during colder conditions or defrost cycles. https://www.partshnc.com/mrcool-5kw-universal-heat-kit-uhk05