I have a rectuangular suppluy and return system that feed from from furnace at one end of my basement. It has two main leads out. They branch off and finally reduct to a single duct at the far end of my house. I'm looking to put in a drop celling and would love to swap out my existing duct work with PCV, can I do that? Does anyone know pros or cons on this?

Thanks

Probably not. I need to know more, how much do you want to swap out?

What exactly do you plan? Any replacement ductwork would need to be the same size. Even slightly smaller ducts would be much more restrictive.

I have a 12' section that I want to replace with possible 4" PVC pipe that I can route through my joists. This will allow me to put in a zero clerance drop celling and thus a bathroom in my basement. So I woul keep the current shet metal from the furnance/ac plenium out for about 10 feet, then convert to PVC or something that I can route through the joinsts fro about 12' then go back to the shet metal from the rest of the run.

PVC duct unless listed are not approved for air movement is a residential structure. I know of no pvc duct that is listed at this time. Fire hazzard will not maintail fire blocking between floor levels like metal.

You cannot go through the joists with anything.But you can go between them with ductwork... There are many sizes of metal ductwork that will do the job...