Why are ducts usually metal? PVC seals much better, and everything else is plastic, or so it seems, these days.
I’m thinking about incorporating plastic (and/or concrete) into my renovation as the air returns, perhaps even exposed, like in commercial buildings. Haven’t priced the concrete yet — for vertical returns — but if I can use it for structural support as well as air movement, it may be cost-effective. Yeah, I know it’s weird. I live “outside the box.”
Replies
Cost. Most new ductwork I'm seeing anymore is flexduct, the spiral wire with fiberglass insulation surrounding it. Only problem with flexduct is animals tear it up in crawls. But maybe someone else has different problems? Sheet metal has better airflow characteristics, less static pressure loss over a given distance. I work with bigger PVC pipe sizes at times, it seems like the sizes you would need for ductwork would be enormously expensive - 12" sewer pipe is $8 a foot or something?
remodeler
I've never seen plastic duct runs except in industrial settings to vent corrosive vapors.Commercial buildings more often than not use the area above the lay in ceiling as an open return air plenum.Plastics,and PVC in particular, are so toxic in fire conditions that with plenum ceilings,all of our open cabling has to have specially rated plenum insulation.If you leave PVC elecrical conduit in a hot box just a little too long,it starts to give off a gas that won't let you take a breath.Not a good material for moving environmental air.
MTIC,
The first and usually overlooked reason (in this forum) is that most buiding codes require ducts for supply and return be made of a select list of materials, none of which include PVC. Visit the box for alittle while and find the code that applies to your situation. Read it. There may be some alternatives to consider.
Tim