All, My home has a high efficiency forced air furnace, with combusion air and exhaust through two PVC pipes (about 15' runs).
While at the heated pool in our neighborhood, I noted that the pool heater was ducted through what appeared to be a single pipe (pipe in a pipe), with the exhaust through the inner pipe and the intake through the outer pipe.
If I understood the arrangement, I could see a few advantages:
1) The inner exhaust pipe would have counterflow to the intake, and should heat the intake air somewhat.
2) The inner pipe had a screen over it, to prevent entrance of critters. I put 1/2" hardware cloth over my intake pipe to prevent the entrance of barn swallows, but it capped over with snow in the winter. This arrangement looked to be a little more robust.
Is this sort of arrangement available for a forced air furnace? What is this called?
Thanks, Chris