Large extension to chimney

  • Active since 1995, is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.


New Member
Nov 1, 2023
Boston, MA
We had a blaze king insert installed in 2019, which never really burned well. It took a long time to light enough to close the door, went out frequently, back puffed, and frequently put out very noticable amounts of smoke into the house. After years of assuming that this is my lack of skill and experience as an operator, i finally got on the roof and measured the length of the flue. The total length is around 11 feet, and the manual from blaze king recommends a minimum of 16 feet, given the use of a 30 degree elbow.

Is it possible to add another 5 feet in class A pipe? Would we be better off with more, or fine with less? The current flue is an insulated 6 inch stainless liner, going up a masonry chimney which is lined with clay tiles. The chimney is on the apex of our roof, which is metal. The masonry chimney protrudes around 3 feet from the top of the roof.
That's pretty short. Adding 3-4' to the chimney could make a nice difference.
Thanks - I did plenty of research here, making sure to get an insulated stainless liner etc, but neglected to measure the length of the flue....
Another question raised by reading other chimney extension threads is whether this can be done with just a bolt on class A pipe and an anchor plate with a new cap and spark arrestor. When i raised this issue with my chimney guy, he mentioned adding another tile to the top of the masonry would be required. Is this correct? It seems others haven't needed this, and I'm not sure if this applies to my situation or not.
There are multiple ways to skin this cat. The chimney could be built up after an extension is coupled to the liner. Or there is the option of using an anchor plate and transitioning to class A chimney pipe.