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Venting a natural gas condensing boiler up a masonry chimney

Question asked by j.lohr on Dec 11, 2017
Latest reply on Dec 12, 2017 by cdafd

My masonry chimney has two side-by-side clay flues. The sizes of the clay flues are 12"x8" and 12" x12". The centers of the clay flues are 17" apart. The larger clay flue vents a wood burning fireplace. The smaller one vents an oil-fired boiler for hot-water baseboard heat.


My HVAC contractor installed a high-efficiency natural gas condensing boiler to replace the oil-fired boiler. The combustion venting of the condensing boiler is Polypropylene (class ii 230F) extended up the smaller clay flue previously used for the oil fired boiler.


The Building Department is balking at this installation,


I can't find anything that addresses this in NFPA 54 - National Gas Fuel Code, or anywhere else.


The boiler manufacturer venting instructions only state that the venting of their condensing boiler up a masonry chimney must be in a flue dedicated for their boiler.


Has anyone run into this before, or have a reference for me to look at?


Some help would be appreciated.