This reversible left or right hand return air support box and plenum kit is for use with systems where the return air must come in underneath the furnace or air handler. The kit includes 8 feet of 24 inch by 8 inch sheet metal ductwork that can be custom trimmed to the correct height for most applications, and a support box that can hold a furnace or air handler up to 22 inches wide. The support box features an interior support bracket for maximum strength, and a 20 by 25 inch filter slot that can accommodate a one, four, or five inch thick media filter. This kit does not include a filter. Please click here to see our recommended filter. For return air box only, please see the Snappy SBFD30 .