Lots of buildings have rigid metal ducts. And lots of buildings have (much-maligned) plastic flex ducts. But why do rigid plastic ducts not seem to be a thing in North American construction? Such ducting would seem to solve a lot of problems: Like flex duct, it would be cheap and fast and easy to install, but give better static pressure due to its smooth walls like metal ducting. Whatever plastic they make flex duct out of seems temperature-resistant enough; why not make rigid plastic duct segments out of the same material, with it being field-assembled like PVC or ABS pipes?
Is there any reason why you couldn't use sufficiently large diameter rigid ABS or polyethylene pipes for ductwork if you wanted? These are both relatively temperature-resistant plastics (176f and 221f, respectively) and would seem to be especially well-suited for carrying the output from heat pumps where the maximum output temperature is much lower than what a gas furnace can do.
Best Answer
1) cost. plastic is way more than steel
2) weight. so much heavier per unit volume
3) thermal expansion and contraction, deformation, etc.
4) it is used in lab environments for fume extraction, and in exhaust for high efficiency gas appliance exhaust (for its resistance to corrosion from the combustion gases)
5) you also cannot use rigid plastic ducting for interior air distribution for fire spread reasons. the fire code forbids it. imagine a flamethrower coming out of your vents as a small spark is fanned to superheated air as the forced air fans the flames from the burning plastic.