Hi.

Is there a replacement for typical metal HVAC ducting in CPVC, PVC, FRP,  other rigid plastics, in 15cm(6") to 30cm(12") ?

Something with smooth inside surface, to be insulated on its outside ?  Perhaps ~1mm wall  with available elbows, tees, connectors available ?  -Not flexible 'hose'-

What is 'schedule' 5, 10 ?

The building codes require ducting to be metal to prevent fire from having an avenue to spread between rooms and floors, the gypsum board is part of the same overall strategy to slow the spread rate of the fire to increase the escape time.

Thanks.

That is good logic for fire-prone structures built with papered gypsum and sticks as in U.S.A.  Not the same for other construction materials, other building codes.

18 hours ago, Externet said:

Hi.

Is there a replacement for typical metal HVAC ducting in CPVC, PVC, FRP,  other rigid plastics, in 15cm(6") to 30cm(12") ?

Something with smooth inside surface, to be insulated on its outside ?  Perhaps ~1mm wall  with available elbows, tees, connectors available ?  -Not flexible 'hose'-

What is 'schedule' 5, 10 ?

Pipe comes standard in it's outside dimension. For pipe 14" and large it is the same OD as the nominal size (so 14.00 +/- tolerance for a 14" pipe)

The OD of a 6" pipe is 6.625" and a 12" is 12.75". A schedule 5 will have a thinner wall than a schedule 10, for the same nominal size.