Thread: Masonry Chimney used only for furnace and water heater

I know chimneys that serve wood burning fireplaces need to be a minimum of 3 feet tall and project at least 2 feet above any structure within 10 feet. However, if the chimney only services a furnace and water heater do these rules apply? I know metal furnace flues can be much shorter. I can't seem to find references for masonry chimneys not serving fireplaces. Thanks.
chimney.jpg

The code addresses "chimneys" without reference as to the fuel or appliances attached.
HTH

Looks like the chimney was existing to the original structure and years later the addition was added to the right of the chimney.

Originally Posted by Raymond Wand

Looks like the chimney was existing to the original structure and years later the addition was added to the right of the chimney.

You are correct sir.

I would call for a metal liner, properly sized for the two gas ppliances. Properly sealed at the top with a metal cap.

Originally Posted by John Kogel

I would call for a metal liner, properly sized for the two gas ppliances. Properly sealed at the top with a metal cap.

And then the masonry chimney code no longer applies? I have wondered about the large discrepancy between B-vent and chimney specs terminations. If a B-vent is slid down a chimney, what then?

Originally Posted by John Kogel

I would call for a metal liner, properly sized for the two gas ppliances. Properly sealed at the top with a metal cap.

Thanks John. And to the others who offered their advice.

The type of liner, whether tile or metallic, does not change the fact it is encased within a chimney or not so the 3/2/10 rule applies whether it is a masonry or factory built chimney. Vents have their own rules. You see, the code considers one may at some future point, convert the chimney to solid fuel and that 3 ft. min. is needed so sparks cool off and die before reaching the roof. Vents don't see sparks. The 2/10 rule is a function of wind effect over roofs and adjacent structures. The intent it to get the termination above any high pressure zone created as wind hits the structure/ roof.

B-vent can be inserted down a chimney if the mfr. allows it but it is still inside a chimney so 3/2/10 applies.

From the pic provided, it will require a liner for sizing if nothing else as that 12" square flue will almost certainly violate the 7x rule for the WH. Since this is a change to the chimney, a level II inspection is triggered.
HTH