Originally Posted by S-F
Did you find my threads on this stuff? Or maybe it was only one thread. There are motorized baffles that go at the end of an insulated duct that only open then the burner fires up. Ironically, about a week after I went through that whole process I visited my grandmother and she had recently gotten one of these things installed. She called it a "fan in a can".
Yes, I read that thread when I was thinking about doing that to my furnace too. I think the main problem is that these non-condensing furnaces are not designed to handle condensation, and the vent has to maintain a high enough temperature to get the water vapor out of the building without condensing in the vent itself.
Were you successful in installing the motorized damper and fresh air vent? I'm not about to unload that much money on a motorized vent, but I did find these manual backdraft dampers at amazon for a good price.
Fantech RSK 4 Backdraft Damper 4" Duct
They are basically just a check-valve that only lets air flow in one direction. I might use one of these in my install. But if I'm sealing both the furnace and water heater burner compartments, it won't really matter if there is a little bit of convective flow when the units are off.