HAC RETROFIT CEILING ASSY 24IN TO 24IN RACK W/ HDW Mixing of hot and cold air streams in the data center lowers availability of IT equipment. Returning the warmest possible air to the computer room air conditioners increases the efficiency and capacity of the system. The hot aisle containment system ensures proper air distribution by completely separating supply and return air paths. This product is a retro-fittable ceiling Assy 24" to 24" rack with HDW.