have you ever seen 1 like this (vent pipe)

[appltech1]

I was following up on an inspection report about a cracked heat exchanger in a goodman gas furnace(horizontal in a crawl space). Yes 1 of the cells has a long crack easy to see. My question is about the 5 in single wall stack pipe. It leaves the furnace goes 10 ft horiz. goes thru the brick and block foundation then turns upward with a 90, enters 7 or 8 inch single wall pipe, rises 25 ft , goes thru the soffet then out the roof and exstends past the roof line apout 4 ft. Anyone else seen 1 this way? If i deside to use another 80 plus furnace can i use the same vent. Im going to ask an inpector to look at it with me but I just wanted your input. Thanks.

[BaldLoonie]

Vent in a crawl space should be double wall. 7-8" single wall way too big for a furnace also.

[MechAcc]

http://hvac-talk.com/vbb/images/icons/icon14.gif Loonie's right vent is wrong and could be a contributing factor to heat exchanger's demise.

[Black Adder]

Must use "B" vent to vent exterior pipe, also must be contained in a shaft or chase and insulated or you are asking for big time condensation problems as well as possible back venting due to the furnace vents inability to overcome all that cold air contained in the vent pipe. The key to good venting practice is to keep the pipe warm in order to create a good draft. If piping is run through a lot of unconditioned space it will not vent correctly. This will certainly go a long way towards destroying your heat exchanger. A naturaly vented furnace is not a condensing furnace but it will sure act like one with a freezing cold vent.

[t527ed]

go 90% furnace and rip that crap out.