Venting question

I’ve never seen a setup like this one -

The vent on the right is from hot water heater #1.
The middle vent is from the second floor gas fired boiler.
The left vent is from the first floor forced hot air furnace.
There is an additional hot water heater that joins the manifold just out of the picture.

If I’m not mistaken, smaller units should join the vent after/over the larger units. Does this look ok?


Not sure, but I think that if the vent stack is inclining, then it should be OK…

Most manufacturers recommend a 10 - 12 inch vertical rise on the vent before elbowing the vent. Don’t see that on the water heater. Write it up for the trades to check especially if you see evidence of spillage at the draft hood area.

Bill, AGA (American Gas Association) and GAMA (Gas Appliance Manufacturers Association) have publication called “Venting Tables Category 1 Central Furnaces” that might help you. It shows examples of multiple fan-assisted and natural vent combinations and the requirements for vent size and capacity.

I believe you are correct. The smaller appliances should connected to the highest available points above the larger appliance vents.


What a lousy potentially dangerous install!

My local gas company training tells me this:

These should all be cat 1 natural draft appliances… NO mixing of negative pressure and positive pressure should there be any!

Notice the draft hood on the water heater? Take a look at the slope of the flue after the hood! Wrong! Wrong location since it is smaller in diameter then the rest of the flues (Fau’s) The smallest flue should be closer to the chimney then the larger one. So much more here… The hood also looks as if there could be evidence of excessive rusting telling me that draft / draw is improper…:frowning:

The slope period!!
The size of all these flues in that contraption of a connection! No “Y” gradual sizing connections just one big “manifold” deal…
Sizing issues with respect to all appliances working at the same time and one working by itself!! :frowning:

GAMA or local gas company requirements ,check the installs regarding Chimney (perhaps no liner to) size and BTU’s/ appliances per sizing… Seven times rule and so on… Even the Mfg. Installation instructions are # 1 to look at first then AHJ since the appliance Mfg.'s use GAMA guidelines for design…:smiley:

Excellent post - Thanks Patrick.