\ v Hart&Cooley. SUBMITTER DRAWING ~ install confidence POLYETHYLENE VAPOR BARRIER FIBERGLASS INSULATION CORE FIBERGLASS SCRIM WIRE HELIX CORE Two plies of black polyester film encapsulate a steel wire helix. Rated pressures 12 in. W.C. positive, 3/4 in. W.C. negative & 1/2” W.C. negative *Recommended maximum operating pressures (ADC Test FD 72-R1): 6 in. W.C. positive for 12 in. diameter and under. 4 in. W.C. positive for 14 in. diameter and over. *Rated maximum air velocity: 5000 FPM.