Chimmney too small?

Mike Murray

Yes there is a formula but it is complicated. Very complicated in fact! Venting tables exist to make things easier but even that's not as straightforward as you might believe.
Some things you'll need to know besides the obvious inputs of the combined appliances are the category of the appliances (can't common vent different categories), whether any are induced draft or gravity vented, chimney height from the highest draft hood elevation to the chimney cap, etc.

You would be best to call in a pro as there are too many variables and available configurations to offer a simple answer without seeing it.

Leon in NJ

I have a 7in steam boiler vent on my chimmny now and would like to add 2 3in natural draft vents from 2 gas water heaters piped in series. How can I find out if the chimmny is big enough to handle all the draft? Is there a formula?

Mad Dog

Don't take a chance...CO KILLS!!!!!

try Find a contractor in NJ for a pro. Mad Dog

Jack_23

Chimney specs

How tall is the chimney? What dimension is the chimney liner? Is this related to a post about this a couple days ago? is the boiler Oil? What is the boilers firing rate? Is the chimney interior or end wall (exterior)? If this is the question form a couple days ago...the same ?'s apply. Is the chimney lined? By code this can be done BUT the other guys posting are absolutely spot on. Every system has a personality and there is a bit of Jeckyl and Hyde in all of them. Your problem would likely occur in the off heat months where you do not have the heat of the oil burner to help the very low btu's of the water heaters.