Masonry Chimney used only for furnace and water heater

[Tom Cissell]

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.
29555

[Bob Harper]

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

[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.

[Tom Cissell]

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.

[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.

[Mike Lamb]

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?

[Tom Cissell]

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.

[Bob Harper]

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