I think it's one of those things where the codes might not be specific. I would be fine with using PVC for general or toilet exhaust. Maybe not for hot exhaust due to temp. limitations...
The duct construction shall conform to the following applicable Sheet Metal and Air-Conditioning Contractors’ National Association, Inc. (SMACNA) standards:
(a) Accepted Industry Practice for Industrial Duct Construction
(b) Rectangular Industrial Duct Construction Standard
(c) Round Industrial Duct Construction Standard
(d) Thermoplastic Duct (PVC) Construction Manual
(e) Thermoset FRP Duct Construction Manual
...so it looks like NFPA is okay with it, so long as it conforms w/SMACNA.
to clarify the question I have a friend who put regular white PVC used in pluming in his basement as ductwork for a forced hot air system. he was finishing a previously unfinished basements and wanted to rearrange the existing duct work. He is doing the job without a permit and therefore with out inspection. I am a structural engineer and do not have access to any of the standards listed. I was concerned that the use of the material would violate NFPA or similar. It is currently a working system I was just wondering if he will run into trouble down the road with either performance problems or problems selling the house. The answers I am getting seem to be conflicting.
I would definitely not use PVC for forced hot air.
I can't imagine that it is covered by code.
Even though you are not holding any pressure, PVC pipe is rated @ 74 F, so if it gets warm it's strength will go down so the pipe/duct will be sagging and bent all over the place. You also might pick up some smells and VOC's.
Since this is for ductwork, this is going to have to be pretty large pipe (unless it is some kind of high velocity systems) and there fore pretty expensive. Fittings are expensive too.
PVC is often perceived as "cheap" even though it is actually kind of expensive.
I have customers hook up chillers to PVC, and turn of the refrigeration system but not the pump. Lots of sagging pipe the next day.
I syde with Clyde. Especially his point about the VOCs. For bathroom exhaust, sure. Heat? not a good idea, especially with the cement used to bond the piping...
Using PVC for ductwork is NOT recommended. The flame spread and smoke developed for PVC piping does not meet the ASTM E84 guidelines of a flame spread index of less than 25 and a smoke-developed index of less than 50 which is specifically prohibited in plenums.
ASTM E84 is why almost all Automatic Temperature Control installers only use plenum rated cable (teflon coated) even if the job doesn't have a plenum. Once bitten, twice shy so to speak.
I wouldn't use pvc, I would use flex duct if I needed the installation to have some sort of flexibility for the future.
I don't see what advantage this person thinks there is by using PVC. The cost of single wall sheetmetal round fittings and pipe that you can buy off the shelf at Home Depot or Lowes would probably be cheaper and the right stuff for heating duct. Either one would need to be insulated but I would not use the PVC for HVAC duct.
I believe the International Mechanical Code allows PVC ductwork where buried in concrete. I'm sure this has to do with the fire/smoke issues previous posters have mentioned.
