This "H" shaped fiberboard plenum is a ducting option for the SpacePak ESP-4860 (BM-2613-1) , ESP-4860EH4, ESP-4860EH2 or the ESP-4860V (BM-2505) high-velocity air handlers. These specific air handlers have some additional plenum installation requirements that the smaller units do not due to their twin blower arrangement.
Two separate square plenum pieces can be used, but this "H" piece takes the guess work out of balancing between the two runs.
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