Masonry chimney
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Thread: Masonry chimney

  1. #1

    Masonry chimney

    I am getting prices for a replacement gas hot air furnace. My existing chimney is exterior with 12" x 8" clay flue venting my 125,0000 BTU furnace 6" flue and 125,000 btu max instantaneous water heater 5" flue.

    So if I go with a new high efficiency furnace that is a direct vent, that leaves the water heater as the sole user of the chimney. Are there any firm rules on whether this can be left as is?

  2. #2
    Join Date
    Mar 2004
    Location
    SE Michigan
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    17,778
    Unless you want to rebuild that chimney, youre going to need a liner kit for the WH, especially if the chimney has 3 sides exposed. It may be difficult for that WH to keep the chimney warm enough to geta good draft.
    "Politicians are the lowest form of life on Earth. Liberal Democrats are the lowest form of politician"

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  3. #3
    Join Date
    Jun 2004
    Location
    Howell, Michigan
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    16,168
    and it won't meet code either.......................!

  4. #4
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    33,829
    Is the WH a natural draft, no inducer motor?

    Simply, code says the flow area of the chimney cannot be more than 7 times the area of the drafthood outlet. If I did it right 5" round is 19.6 square inches. 12x8=96 sq inch chimney. 19.6 x 7 = 137 sq inches. Since the 96 sq inch chimney is smaller, Natual Fuel Gas Code says OK. Local codes might disagree.

    If there is a draft inducer involved, line the chimney period.

  5. #5
    Join Date
    Jun 2004
    Location
    Howell, Michigan
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    16,168
    Quote Originally Posted by BaldLoonie View Post
    Is the WH a natural draft, no inducer motor?

    Simply, code says the flow area of the chimney cannot be more than 7 times the area of the drafthood outlet. If I did it right 5" round is 19.6 square inches. 12x8=96 sq inch chimney. 19.6 x 7 = 137 sq inches. Since the 96 sq inch chimney is smaller, Natual Fuel Gas Code says OK. Local codes might disagree.

    If there is a draft inducer involved, line the chimney period.
    Our local inspector isn't smart enough to be able to figure that one out............LOL! Around here he needs a liner.

  6. #6
    Join Date
    Aug 2004
    Location
    S.E. Pa
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    6,128

    Cool orphanned water heater

    You need a Level II inspection first. That will determine what else in addition to the liner must be done. The liner is required to meet the class of service. It is sized per the gas codes and manufacturer's listed instructions. Once relined, it will contain the flue gases, have a stronger draft and be less prone to flue gas spillage.
    HTH,
    Hearthman

  7. #7
    Quote Originally Posted by BaldLoonie View Post
    Is the WH a natural draft, no inducer motor?

    Simply, code says the flow area of the chimney cannot be more than 7 times the area of the drafthood outlet. If I did it right 5" round is 19.6 square inches. 12x8=96 sq inch chimney. 19.6 x 7 = 137 sq inches. Since the 96 sq inch chimney is smaller, Natual Fuel Gas Code says OK. Local codes might disagree.

    If there is a draft inducer involved, line the chimney period.


    Natural draft for the water heater and present furnace (vintage 1958).

    B vent into chimney. 12 X 8 chimney internal area is defined as 63.6 sq in per Table G-1. Table 11-3 5" flue with 25 foot tall chimney is within natural flow limit. 1996 gas handbook says that Tables 11-11, 12 and 13 are to be ignored for water heaters. My obsolete gas code handbook is from 1996. Just wonering if anything has changed in this code area since 1996.

    Anyhow, I did talk to the gas inspector (MA). He indicated that if the unit does vent properly when he tests it, then it should pass inspection.



    It looks like I have to add 4 CO detectors to the house if I go direct vent furnace. Can't pass inspection without them!

  8. #8
    Join Date
    Nov 2007
    Location
    Westlock, Alberta, Canada
    Posts
    57
    Every area has different standards, always best to talk to the inspector

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