I don’t do a lot of gas furnaces, what should the clearance be between the smoke pipe and combustable materials (wood)?
Thanks!
David lets be professional here no pun intended but the terminology is combustion; not smoke pipe and class be vent pipe in my area is required a 1 inch clearance to combustibles.
1" for B vent
6" for single wall - can be reduced to 1" with proper heat shield
this looks like single wall to me
Also looks like there there may (considerable?) condensation dripping from that top vent (water heater?) at it’s junction (hidden behind the BX) as evidenced by what appears to be corrosion of the the lower pipe (from the furnace?) by dripping water.
In my area this can be a clue that whatever those appliances are connected to (older masonry chimney?) may not be a suitable for venting newer (even Cat I) appliances and excessive condensation is shortening the service life of the chimney and/or vent pipe(s).
Also the WYE connection doesn’t look proper. Has to be ONE formed piece. Can’t be a hole cut in the flue piping with the other inserted.
Whew,
Looks like somebody else trying to be crafty. You can get anybody to do your air conditioning work doesnt mean they are going to install it correctly or in accordance to the codes. I have seen to many people die from incorrectly installed flue vents. This flue should be straped with either metal hanging strap or some other kind of strap for support.
Note:In my area you cannot put any type of screw in the flue vent. It may differ in your area. I recommend checking the county, state and or province building codes.
Looks like SW pipe being used for Flue Venting, at least as far as I can see in the picture. Hopefully double-wall (B-vent) piping is being used vertically through the chase areas and out through the roof.
I recommend getting and HVAC Contr. involved, just to verify what you think you see. If you can meet him/her there, they can probably give you some invaluable information for futre use.
In my area, DW/B-vent piping normally has a 1" clearance, unless you are installing horizontally through an enclosed combustible area, then it goes to 6" and shielded.
If you are installing SW piping, min.clearance is 6" all around (6"+D"+6"), and shielded, and can’t be enclosed within combustible material.
There are probably other conditions I’m forgetting…
Thanks every one for your input. The flue pipe is connected to a B-Vent just above what the photo shows. The owner has a service contract with the local gas company. I have had similar situations lately where furnaces are serviced regularly but the service person does not seem to have called out these clearances. While I did not know the exact clearance required I did refer it to a heating specialist. Probably it will be the same “specialist” who has let it go before. The 6" distance was what I was looking for. No matter what the “specialist” says, I did my part. 
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