I would like to know what the clearance to combustables is for the old transite flue- three or four inch round connected to a residential water heater of residential funace. also the method of connecting to a B vent.
If you could let me know where to find the code section or the manufactures instruction? good luck hey

Original Post
See mechanical code table 8-9; the old transite is equivalent to asbestos cement products. The clearance should be the same as single wall metal pipe (6") unless the old product is clearly lablelled for reduced clearances (some types had a fire clay liner and extra thick walls).
Please clarify your "connection" as stated you want to connect a B vent to the transite, this is not typical. Typical is a metal vent connector between the appliance and the transite, transition must be custom fabricated if the transite I.D. is larger than vent connector diameter.
Hey Jim

Thanks for the reply. Table 8-9 gives me the diameter pipe to be used based on the btu's of the appliance being served with the hieght and lateral offset being considered. Every original installation of the old transite I see has 0 clearance, tight to combustables. I have been trying to contact current manufacturers of asbestos cement products to get there installation instructions although they seem to be for water distribution only.Also as far as custom fabricated adaptors- they're not listed for use?
Unless you can see a "type B" gas vent assembly marking on the transite, it is considered the same as single wall metal per today's codes. Transite hasn't been used for gas vent chimneys for many years and the level of inspections for mechanical even 15 years ago wasn't too good in Contra Costa County (I have a lot of experience in the area over the last 32 years). You will find many old asbestos cement gas vent chimneys tight to combustibles, not too bad a condition if there is a good draft hood like a water heater but can be a heat hazard to wood for an appliance like a mini boiler. Check the ceiling construction, if the ceiling is regular plaster, no problem; if gyp bd, cut at least 2" annular area around the transite pipe; if any wood is part of the ceiling, cut at least 6" annular area around the pipe and make sure no wood is within 6".
A vent connector does not have to be listed product between the draft hood and the type B gas vent chimney, only has to be of the proper metal guage, thus adapter can be custom fabbed and mechanically fastened (very carefully drill the transite & use simpson concrete "blue" screws.
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