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Cement lined chimney will low stack temp be a problem

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Blackoakbob
Blackoakbob Member Posts: 252
in Chimneys & Flues
We had a new burner installed for better dependability replacing a 40 + year old power burner but the new one has a stack temp at <350 degrees F at the breaching and the cement lined chimney goes up 40 ft thru a cold garage. My concern is possible condensing in the boiler or enough condensing in the chimney to detiorate the lining until it fails  the boiler is a fire tube scotch type cica 1965 low pressure steam 
Any thoughts, thank you

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  • Big Ed_4
    Big Ed_4 Member Posts: 2,798
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    A chimney running up though the garage is not bad . North standing outside chimney really is the worse , A liner could not hurt . Size it to the new equipment would be best . A way to see if you really need a liner , on a cool day check the condensate leaving the chimney . There should be a space between the chimney and the condensate ..

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  • MikeAmann
    MikeAmann Member Posts: 998
    edited November 2023
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    I am no expert, but you asked for thoughts....
    I am in the middle of doing a band-aid job on Mom's chimney right now to get through the winter without further damage. At the top, I found missing mortar between the bricks, same between the top 2 clay flue liners, and a tennis ball sized hole in the second liner down. It's within reach, so a patch job is in order. It's too late now to be tearing down and rebuilding. And the crown is a mess. Looks like Dad knew of this and did his own patch job sometime in the past. Last night I found a tub of Henry Patch n' Level and I believe he slathered this stuff all over the entire crown. Did it help or hurt??? I can't say. But I have to remove this stuff before I can do my band-aid repair. And he also used some "asphalt" crack filler which didn't work.

    To answer your question, yes, I believe that low stack temperature will definitely give you flue gas condensation, and that will eat away at your mortar joints and clay liner. I was finding 2+ inches of water in my cleanout. You must get that stack temp up, either by increasing the firing rate, or experimenting with the baffles. I assume that you use baffles like this:

    You can read some of my adventure here: https://forum.heatinghelp.com/discussion/184643/flame-retention-head-conversion-of-wayne-e-series-burner/p5
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
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    Are you sure you’re not underfired?

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    SuperTech
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,575
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    If your net stack temp stays above 330 you should be ok.
  • Big Ed_4
    Big Ed_4 Member Posts: 2,798
    edited November 2023
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    Scotch Marine boiler is very efficient ... The original owner knew and paid for it .

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  • Blackoakbob
    Blackoakbob Member Posts: 252
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    It is in a commercial  building and a commercial grade prefab chimney  sorry I  didn't  elaborate  more and a wet back scotch style boiler 
  • Blackoakbob
    Blackoakbob Member Posts: 252
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    This new burner is the type that tunes it's  combustion by O2 varying gas and combustion air independently and modulates from high to low output by steam pressure my concern is too efficient (83%) for the old equipment chimney and boiler

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,575
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    @Blackoakbob 83% should be fine in a normal chimney especially with steam
    Blackoakbob
  • Big Ed_4
    Big Ed_4 Member Posts: 2,798
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    Do you mean the burner controls the proper O2 for level of combustion ? That's cool

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