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.