Richard, category I venting only goes up to 83%AFUE. Above that, you need special venting such as AL29-4C listed to 1738 until you get up to Cat. IV when you can use plastic.

You seem to be bouncing all over. One minute we're talking about an aftermarket power venter used on an 80% furnace power vented out horizontally with single walled leaky pipe under positive vent pressure and now you're talking about vertical venting with single walled pipe to B-vent, which IS the normal, accepted, listed means of venting a Cat. I furnace under negative vent pressure.

IMC 801.9 Positive Pressure "Where an appliance equipped with a forced or induced draft system creates a positive pressure in the venting system, the venting system shall be designed and listed for positive pressure applications"


FYI, some techs will put a longer post purge on just to clear the exhaust gases so there're less chance of spillage or condensation at standby. In the case in point, once that power vent cycles off, you have warm moist gases trapped in the horizontal vent with no draft to evacuate them so they cool and condense as seen.

" Since the addition of the external draft inducer it increased the air flow thru the exchanger without increase of the flame, decreasing the flue gas temp and increased the flue pipe pressure causing condensation and leakage of the condensation and flue gasses by increasing the pressure exerted on the interior of the flue pipe. Do I need to continue?" --- Huh? I'm sorry but does anyone else see this as a cohesive thought?


"Might I remind you, This IS what I do every day for a living and I am the best at what I do." ---Well, at least you're humble.....

Have a good day, ;-)
Bob