Report 6" ducting in General Woodworking Talk Posted July 7 So I'm finally getting around to re doing my ducting. I had smaller DC before and used 4" SD straight pipe with pvc joints. I got a much more powerful 3HP 1600 cfm DC a couple of months ago and want to upgrade to 6" for the main lines with 4" drops. While I would love nordfab (or similar) it's just way to expensive for me. I'm leaning towards spiral ducting unless someone can persuade me otherwise. If I go with metal ducting what gauge should I get? Doing a quick search most of the local hvac places carry the 6" diameter in 26 gauge. Will that be substantial enough?