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  1. #1
    Join Date
    Dec 2007
    Posts
    4

    gas vent termination height?

    My question concerns the termination height above the roof (4/12 in this case) of a 5" BW vent. There are no walls, vertical or otherwise, on this roof.

    I read the code to say the minumum height is 1 ft.

    My HVAC guy reads this "Gas vents 12 inches (305 mm) in size or smaller with listed caps shall be permitted to be terminated in accordance with Figure G2427.6.5, provided that such vents are at least 8 feet (2438 mm) from a vertical wall or similar obstruction.", to mean I need 8 feet horizontally from the roof surface as it's a "similar obstruction".

    As far as I know he's right about everything else. Is he right about this?

    Thanks.

  2. #2
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,754
    3' minimum thru roof, 2' higher than anything within 10'

  3. #3
    Join Date
    Dec 2007
    Posts
    4
    Hmmm.... I must be reading this incorrectly, or reading in the wrong place?

    UMC 802.6.2 says Type B < 12 in diameter min 1 ft above roof up to 6/12 slope.

    Doesn't apply in my case, or I don't understand it?

    Thanks again.

  4. #4
    Join Date
    Apr 2004
    Posts
    7,680
    2' above anything with in 10'.

    I would have to probably do the math but if you have a 6/12 slope (45 degrees).... Nevermind, my brain is fried, but it's safe to say Chimney's dont vent as well as they used to because they are blocked from wind too often when cosmetics become more important than the heating system.

  5. #5
    Join Date
    Sep 2002
    Location
    Boise Idaho
    Posts
    1,032
    you need to be 12" above the roof as long as the pitch is less then a 6/12. also must be clear of windows and overhangs above it .

    matt

  6. #6
    Join Date
    Dec 2007
    Posts
    4
    No problem with cosmetics here, I'm just trying to understand the code!

    I see chimneys and single wall vents listed as needing to be 10 feet from the building, but not Type B? My thinking was, if you need to be 8--or 10--feet horizontally from the building, what's the point of the table IRC F2427.6.5 or UMC F8-2? Wouldn't the numbers in those tables be meaningless?

    Thanks.

  7. #7
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,225

    Cool

    You go by the mfr's lised instructions. The 3ft through the roof requirement is for "chimneys"-not vents. You said "BW" vent first now "B" vent, which is it? BW is listed for wall furnaces only. Round vent is B vent. Still, get the mfrs. manual and follow it.

    Generally, the codes and listings will call for a min. of 12" through the roof. However, if in the snow belt, you may need much more. Then, you measure to see if within 8 feet of an adjoining structure. This is typically where the vent exits a lower roof that approximates the second floor of the home. If it is within 8 feet, then it must extend 2 feet above any point within 10 feet. Once you get over 5 ft above the roofline, it must be properly supported.

    Now, you must check your local codes. They may have an ordinance that exceeds these stds. You always go by the most restrictive codes.

    HTH,
    Hearthman

  8. #8
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    No truer words were wvrt spoken.

    I live in an upscale neighbor hood and some of the brick chimneys were built too short and the furnaces they served had a great deal of difficulty venting properly.

    They took the el cheapo way out and added three feet of 20ga galvanized fabricated to flue size outlet.

    Man does it look cheesey. There is even monster brick bar b que inone back yard that could handle a whole side of beef. The bar b que is a masonary work of art but when they fired that baby up and cooked, the smoke was so thick it blinded traffic on a busy mainstreet.

    That flue was short by 8 ft. They used galvanized again and ruined the looks of the bar b que.

    Just thought that would be of intrest to whomever.

  9. #9
    Join Date
    Dec 2007
    Posts
    4
    I checked the manufacturers literature: "Minimum height from roof to lowest discharge" at pitch less than 7/12 is 1 foot.

    It also states "...terminating a sufficient distance from the roof so that no discharge opening is less than 2 feet horizontally from the roof surface.....".

    Both those statements are in accordance with the way I read the code.

    I'm still confused by the widely varying answers here, and from my HVAC guy--who as I said, I think really knows his stuff. Is this more complicated than it seems? What am I missing?

    Thanks again.
    (It was type B, not BW--sorry--though I think the code treats them the same as far as height above roof.)

  10. #10
    Join Date
    Jan 2007
    Location
    N.E. Ok.
    Posts
    1,370
    Follow the mfg.'s install instructions, they are tested and will override general code rules.(in most locations)
    This is hart and cooley product,(B-vent) fairly simple. http://www.hartandcooley.com/vent/si...on%20guide.pdf

  11. #11

    Hmm

    2 ft. higher than anything within 10 ft. can't go wrong. scrimping is never a goood idea.

  12. #12
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    i ave always gone by 2ft above the ten foot plane of the roof

    this alows the exhause to raise above the roof and be taken away

    i have seen some a few feet out the roof and the wind just blowing it back down along the roof

    not worth cheaping out. You want the exhaust to go up and away

  13. #13
    Join Date
    Nov 2007
    Location
    Chicago
    Posts
    76
    Quote Originally Posted by tab a View Post
    No problem with cosmetics here, I'm just trying to understand the code!

    I see chimneys and single wall vents listed as needing to be 10 feet from the building, but not Type B? My thinking was, if you need to be 8--or 10--feet horizontally from the building, what's the point of the table IRC F2427.6.5 or UMC F8-2? Wouldn't the numbers in those tables be meaningless?

    Thanks.
    I don't know where you get 8 or 10 feet. You can't exhaust within 10' of the property line or within 10' [or 12 or 15 depending on the local code] of a fresh air intake.

    The vent must terminate a minimum of 2' above any part of the roof within 10'. Depending on location, you also want to make sure that it is above the possible snow drift accumulation line.

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