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  1. #1
    Jeff Eastman's Avatar
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    Default Combustion air venting location

    Last edited by Jeff Eastman; 12-19-2007 at 02:43 PM.
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  2. #2
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    Default Re: Combustion air venting location

    should be within the upper and lower 12" per section 702 of the uniform mech code.


  3. #3
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    Default Re: Combustion air venting location

    Quote Originally Posted by brian schmitt View Post
    should be within the upper and lower 12" per section 702 of the uniform mech code.
    They are.

    Jeff was asking if the entire vent had to be.

    The answer is 'No.'.

    As long as at least the top of the top vent is at or within 12" of the ceiling, that is okay.

    Likewise, as long as at least the bottom of the bottom vent is at or within 12" of the floor, that is okay.

    The entire vent opening does not have to be within that 12".

    One could conceivably make a 12" square opening, turn it on the diamond with one corner up, and, as long as that one corner up was at or within 12" of the ceiling, that installation would be acceptable.

    The idea between the two vents is to get air circulation in the room, the appliance then draws its combustion air from that circulating air.

    Jerry Peck, Construction / Litigation Consultant
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    Talking Re: Combustion air venting location

    jeff,
    jerry is wrong this time. the code explicitly states within the upper and lower 12'. it does not say "starting within". has to do with equilizing pressure. manuals to the mechanical codes clearly depict the proper locations. email a fax# and i'll shoot you a copy.


  5. #5
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    Default Re: Combustion air venting location

    2006 IRC illustration M1703.2(2) shows the two vents and outlines the space between the top of the top vent and the ceiling, and the space between the bottom of the bottom vent and the floor, and for both of them it says less than or equal to 12 inches. So the top of the top vent can be a maximum of 12 inches from the ceiling and same for the bottom vent and the floor, so, in fact, the entire vent(s) can be just outside of the 12 inch space. At least, that's how it looks to me.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
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    Default Re: Combustion air venting location

    You can find the illustration I mentioned at
    Seattle Residential Code .
    Click on Chapter 17, Combustion Air over on the left, then scroll down about half way and you'll see it on the left.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
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  7. #7
    Bob White's Avatar
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    Default Re: Combustion air venting location

    Here's the illustration John was writing about. (I think -- if I uploaded the pic correctly)

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    Default Re: Combustion air venting location

    Quote Originally Posted by brian schmitt View Post
    jeff,
    jerry is wrong this time.
    Brian,

    I've been wrong before, many times, and will be wrong again, many times.

    But not this time.

    I get this information not only from the courses I've taken presented by others, but presented by the ICC themselves, and, when I have questions and call the ICC to ask for clarification.

    What I stated in my previous post is what I have been told by the ICC.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Combustion air venting location

    Bob - Yep. That's the one.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
    www.ArnoldHomeInspections.com

  10. #10
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    Talking The "opening" question

    M1703.3 "One opening shall be within 12 inches of the top of the enclosure and one within 12 inches of the bottom of the enclosure".

    Now compare with IFGC 304 uses the phrase " commencing within 12 inches of the ....." Notice it did not say "reside entirely" or similar language. Compare this to the sections on emergency ingress and egress where it gives a reference point-- the sill height 44" above the floor. If it was that critical, they would have been more specific but this is intended to be an approximation. The air does not carry a ruler or go/ no-go gauge with it: Nope, I ain't going in there, the measurements aren't to spec. Air doesn't belong to the unions yet.

    Guys, I think you're trying to pick fly poop out of black pepper here. If the opening starts within 12 inches of the floor or ceiling, it's cool. If it's within 14 inches, I'm not bitching. If its 2 feet away, I'd probably call it out. You gotta be reasonable here. The 12 inch thing has to do with not only room pressures but the natural convection patterns usually seen in heated homes.

    If you stand in the middle of the room and rotate your arms in big circles like a helicopter, apply this motion to air flows. As room air hits the cool outer walls, it becomes denser so it falls to the floor. Warm room air rises up, hits the ceiling then mushrooms out to the walls, down, cools and completes this cycle. Smoke does the same thing during a fire. That's why the instructions tell you to place smoke and CO alarms about 18" from ceilings and walls. This phenomenon is known as the "cold corner effect". Very little air travels tight into the corners. Therefore, if you want to join in the room air, you have to have your entrance and exit ramps far enough away from the corners so traffic can flow smoothly, so to speak.

    HTH

    Keep the fire in the fireplace.

  11. #11
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    Default Re: Combustion air venting location

    i like the illustrations! looks like one of them can support the not within 12" opinion. the others clearly support the wording in the code. the written word of the code trumps the picture book in the code enforcement business. the code officials can interpret info and make an alternate decision based on the written word. this is like barbequing beans=some fall thru the grill. i would not lose sleep over minor erroes. the purpose of the upper opening is to ventilate heat build up from the appliance enclosure.as the air surrounding the equipment is heated,it rises to the top of the enclosure and is at a slightly higher pressure. unless the pressure is relieved, it will continue to build and can prevent the inward flow of combustion air to the lower opening, thus witin 12" of the top and bottom. i am new here and appreciate the sharp minds and spirited debates! fun place!


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    Default Re: Combustion air venting location

    I will frequently find this - almost right!

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    Eric Barker, ACI
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    Default Re: Combustion air venting location

    Quote Originally Posted by Eric Barker View Post
    I will frequently find this - almost right!
    Except that because it has a metal grill on it, it now needs to be at least 144 square inches instead of 100 square inches to allow for the blockage caused by the metal louvers. How high is the ceiling on the other side where the water heater is? even with this lower ceiling, or higher? If higher (at 8 feet), then its ... close but no seegar.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Combustion air venting location

    Well actually this main issue with this was that the grills share the same stud cavity - they basically cancel each other out. Have to have separate sources.

    Eric Barker, ACI
    Lake Barrington, IL

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    Default Re: Combustion air venting location

    Quote Originally Posted by Eric Barker View Post
    Well actually this main issue with this was that the grills share the same stud cavity - they basically cancel each other out. Have to have separate sources.
    Okay, you got me on that one, I figured the openings were wrapped within the stud cavity and went through to the other side of the wall, allowing one confined space room to communicate with the space on the side in your photo.

    Jerry Peck, Construction / Litigation Consultant
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