PVC for intake and exhaust gases?...................
Surprisingly, yes. Condensing furnaces and water heaters extract the latent heat of vaporization from the flue gas. The flue gases are down around 100F to 110F, well within the PVC operating range. Plus, the gases contain corrosive products and plastic stands up to them really well.
Our Bryant Plus 90 forced air furnace is a condensing furnace and uses PVC for air inlet and exhaust outlet. The pipe is concentric, a pipe within a pipe. These are standard installations now.