Ok, I think I have found out the secret to attaching photos. I think?? OK, boys and girls,here we go. I need all the help I can get on this one. As you look at the picture you will see two gas hot water heaters combined to go out the ceiling throught one single lining flue. Also, there is a flue from the direct vent fireplace with zero clearance to the ceiling board and the back of the fireplace is directly against the hotwater heater. This all in an exterior closet of about 4’x3’. the ceiling is covered with masonite. This is all in a 2 million new house.
What you don’t see is the “t” for the TPR valves, and the flex pipe going directly into the housing for the gas fireplace.
I wish I could have gotten a better picture, but as the beginning say, I just figured out how to get the picture in the message. With only 250k allowed, it’s hard to get a good picture. Anyway, as the message says, the two hot water heaters are vented into one stack of the same size and out the building. The flue pipe is single wall and directly against the masonite ceiling.
Russell can not see anything in the pic but can tell you single wall pipe is not allowed to penetrate beyond any dry wall ceiling and double wall class B vent must have one inch clearance to combustibles.
Two appliances cannot be connected or Tee together without an increase in size of the flue pipe. ( size of the trunk line+ 50% of the second pipe.)
In this State single wall pipe can only be used within the equipment room and has to have 6 inches clearance to combustibles. So it must be converted to double wall 6 inches before it penetrates the ceiling. AHJ for here