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Sealing a brick chimney flue for gas boilers?

DCastle
DCastle Member Posts: 15
in Carbon Monoxide Awareness
Hi: Soon this fall I will be installing twin boilers in the cellar of my 111 yr old home on it's brick chimney. The chimney flue is 9x13" and the "effective height" of the chimney is 36'. One boiler is 59K BTU and the other is 51k BTU (output). The existing setup uses an old aluminum 6" chimney pipe for a liner, and I'm concerned about it having enough draft during the deep of winter (-20 is Minnesota design temperature) for both boilers. Both boilers have a 4" outlet. Before the roofline, the chimney passes through app. 9' of un-insulated attic and I'm worried about lack of enough draft or potential down-drafting because of this cold section. I don't want to use a draft blower because of the noise, and I can't go larger than a 6"o.d. flue liner because it won't fit within the narrow 5' tall portion of the chimney above the roof. What are my options if there are any? Would it be possible to use some kind of a heat-resistant sealer on the inside of the chimney (to gain that large 9x13" flue space) and eliminate the aluminum liner entirely? Maybe they manufacture a 5" insulated chimney flue that would fit?


Thanks, Dale

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 24,983
    You will have to heck with your authority having jurisdiction, but if that masonry chimney isn't lined, in my opinion you will have to have a stainless steel -- not aluminium -- liner. You may or may not be able to get away with both appliances in one liner.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    What are the efficiencies of each boiler?
    I'm assuming gas, but I don't think a 5" SS is going to do both, but a 5 1/2" may.
    What's the diameter at the top of the chimney?

    There was an error rendering this rich post.

  • Bob Harper
    Bob Harper Member Posts: 1,091
    111 y/o had to have fired coal or oil, which immediately disqualifies an aluminum liner.
    You should be fine with a 5" smoothwall or a 5.5" corrugated insulated liners. 316L or 316Ti ss. Manifold both into one liner. You can use a tee as a condensate trap but it isn't required if you need to do a pull-through making a broad radius bend at the base. All ss in the wall--no galvy.
    HTH
  • mattmia2
    mattmia2 Member Posts: 11,026
    There are also oval liners available that will allow you to get a larger vent through the existing chimney.
  • unclejohn
    unclejohn Member Posts: 1,833
    Call the local chimney guy, one with good references. He will know what you can do.
  • gennady
    gennady Member Posts: 839
    Fuel gas code has tables for chimney sizing. You need total input not output of connected appliances.
    Gennady Tsakh
    Absolute Mechanical Co. Inc.
  • DCastle
    DCastle Member Posts: 15
    Gennady: That table is for class C chimney, am I correct? If it is, this solves my whole dilemna! I found a similar table on an InspectAPedia site for class B (insulated chimney), I found that 4" I.D. flue provides 183K BTU capacity as opposed to the 112 I found on your chart... I have more than ample room within the old brick chimney to do the job. Yay!

    Thanks, Dale

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