Chimney cap, one large, or three small ones ?

Discussion in 'Remodel Forum & Blog' started by GG_Mass, Sep 8, 2013.

  1. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    Hello,
    I don't have any chimney caps on my 3 chimneys. They all climb up the same space. One is for the oil fired water boiler, one for the basement fireplace, and one for the living room fireplace (that one has a damper installed).
    Does it make a difference, to the performance of the chimneys, and to other aspects that amateur like myself may not be aware of, - If I'll install one large cap to cover all three chimneys, or an individual sized cover for each one of them ?
    Thank you.
  2. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
    Cave Creek, Arizona
    Whichever is cheaper and looks better.
  3. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    I see,
    Thank you.
  4. Dana

    Dana In the trades

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    2,924
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    01609
    The cap for the oil-burner would rightly be a purpose made terminal for the stainless flue liner, and NOT a general purpose rain-hat type of chimney cap. Oil exhaust is highly acidic, and the condensate can eat up many metal chimney caps, and any condensate that dripped on to the masonry chimney will degrade the concrete chimney top & brick mortar in short years. A single large over-arching rain-hat type would increase both the likelihood and amount of condensate dripping on the masonry, which is not a good idea.

    The fireplaces deserve top-sealing dampers. According to my buddies with the blower-door test equipment the gasketed Top Lock versions seal far better than any hinged version (lightyears ahead of anything installed at the top of the fire-box in the fireplace itself), and becomes essentially it's own chimney cap:

    [​IMG]
  5. GG_Mass

    GG_Mass Member

    Messages:
    49
    Location:
    Massachusetts
    On (sort of) the same subject:
    One of the three flues is for the basement fireplace, which is disabled (wooden boards are hammered on the top of the fireplace). Is there a 'smart' method of sealing the flue on the top of the chimney (where the cap would go) , without spending the $ needed for a cap/damper ? - Being that I don't plan to use the fireplace in the basement.
    Thank you.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,835
    Location:
    Cave Creek, Arizona
    quote; The fireplaces deserve top-sealing dampers.

    NOT if the fireplace has a gas log burner in it.
  7. Dana

    Dana In the trades

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    Mortaring on or silcone-cementing/caulking a concrete patio-paver to the top of the flue liner works. The function is two-fold, limiting the direct rain wetting of the interior of the masonry chimney, and lowering the 24/365 stack-effect infiltration factor. At the bottom end of the that flue at the fireplace it may be worth fitting in a fiber-cement board or wallboard air-barrier at the top of the unused fire-box to limit air infiltration too. Both would be easily removable for inspecting or re-commissioning the flue, and both can be made reasonably air-tight.
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