I'm updating an exhaust pipe on my furnace.
Currently I have 4" steel exhaust pipe coming from my DUKANE MPGA075B3 (75.000 BTUs) (AFUE% = 80%)
I would like to update it to "Thermoplastic Pipe" because it require a 0 clearance to combustion material.
Few questions: Do I have to use a 4" pipe or I can use a 3" pipe?
Can this pipe handle the amount of heat my furnace producing?
Thank you.

I do not believe there is any approved plastic pipe for a 80% unit. There used to be but they had to pull it off the market. B vent can be used but it needs at least 1 inch clearance to comb. If the unit calls for 4 inch pipe you should not reduce it or other damage could happen.

I do not believe there is any approved plastic pipe for a 80% unit. There used to be but they had to pull it off the market. B vent can be used but it needs at least 1 inch clearance to comb. If the unit calls for 4 inch pipe you should not reduce it or other damage could happen.

Thank you hvac1000, do you have any reference (internet link) to "B vent" stuff? thank you

http://www.ventingpipe.com/category.cfm?categoryID=147&source=ggpipe&s_kwcid=b-vent|900914290


here you go.

http://www.ventingpipe.com/category.cfm?categoryID=147&source=ggpipe&s_kwcid=b-vent|900914290

Thank you