Poly Duct & Convection Tube Buy pre-punched or punch your own convection tubing and save. Simply mount un-punched tubing to your jet fan, tie off the far end and turn on the jet fan. Once the tube is inflated, use a small propane torch to heat a tin can mounted on a broom handle and melt the holes at the desired locations. Hole pattern: 2.5" dia. on 24" centers at 4 and 8. This item is NOT UV stabilized, but should last thru the heating season. 4 Mil STANDARD CONVECTION TUBING 500' Master Roll