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  1. #1
    Join Date
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    Default Yet another return air question

    This just looks wrong to me, so it must be.
    Do all the sections in IRC M1601 (Ducts) apply to Return Air vents?

    I opened up the cover of a Return Air vent in a wall that formed the side of a stairway. Inside the staircase was an opening in the floor for a return duct - no ducting between the hole in the floor and the vent opening in the wall (the walls under the stairway were pretty well sealed as most return air ducts are, therefore making the entire space part of the duct.

    Oh, did I mention that there was a Kingsman direct vent gas fireplace a few feet away from the air return vent? What scared the bejuice out of me was that this same space under the stairway is open to the back side of the direct vent gas fireplace.

    Now I know that the fireplace is essentially a sealed unit, the gas lines are all inside the manufacture fireplace assembly, and the exhaust duct should be sealed. So in theory no gas or combustion fumes should escape. However, what IF there ever was a leak?

    IF I was to quote code (which of course I don't), which is the best?

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  2. #2
    Join Date
    Mar 2007
    Location
    Columbus GA
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    Default Re: Yet another return air question

    Almost to many to list
    Electric wires in plenum
    Underside of stairs are unprotected


    In reality that closet is where the return air comes from


    M1602.2 Prohibited sources.
    Outdoor and return air for a
    forced-air heating or cooling system shall not be taken from the
    following locations:
    1.
    2.
    3. A room or space, the volume of which is less than 25 percent
    of the entire volume served by such system. Where
    connected by a permanent opening having an area sized
    in accordance with ACCA Manual D, adjoining rooms
    or spaces shall be considered as a single room or space
    for the purpose of determining the volume of such rooms
    or spaces.
    4. A closet, bathroom, toilet room, kitchen, garage,


    mechanical room, furnace room or other dwelling unit.
    5. A room or space containing a fuel-burning appliance
    where such room or space serves as the sole source of
    return air.
    2.3. Return-air inlets shall not be located
    within 10 feet (3048 mm) of any appliance
    firebox or draft hood in the same

    room or space.
    3. Rooms or spaces containing solid-fuel burning
    appliances, provided that return-air inlets are
    located not less than 10 feet (3048 mm) from

    the firebox of such appliances.



    Last edited by Rick Cantrell; 01-22-2010 at 05:53 AM.
    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

  3. #3
    Join Date
    Mar 2007
    Location
    Western Montana
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    261

    Default Re: Yet another return air question

    Maybe I didn't describe it well enough.

    By my reading, the return vent opening in the living room is within 3-4 ft of a fireplace, but it is a direct vent fireplace.
    M1602.2.2 - 5: Exceptions: The fuel-burning appliance or an appliance not requiring a vent in accordance with Section M1801.1 or Chapter 24.

    This is not a closet (M1602.2 - 1, or 4), but the interior (concealed) wall space under a stairway. Essentially, an oversized stud wall cavity (which is allowed for return vents).

    Unless I am missing a section somewhere, I don't see any requirement for a firewall behind the direct vent fireplace, since in theory, the factory made fireplace is itself a sealed enclosure.

    I did not mention it before, but from my limited view of the exhaust vent from the back of the fireplace, it is very likely that there is NO firestop where the exhaust vent passes up through the floor joists of the 2nd floor of the house to a chase on the 2nd floor. So there are problems there, but that is related to a different set of codes involving the lack of fire stops between floors, not the actual codes that describe the proximity of the fireplace to the furnace return air duct.

    Therefore, because of lack of fire stop between the floors, the applicable code is
    M1601.1.1 - 7.3. Stud wall cavaties shall noat convey air from more than one floor level.
    M1601.1.1 - 7.4. Stud wall cavities and joist-space plenums shall be isolated from adjacent concealed spaces by tight-fitting fire blocking in accordance with Section R602.8.

    But I am certainly open to other arguements.

    Terry


  4. #4
    Join Date
    Mar 2007
    Location
    Columbus GA
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    Default Re: Yet another return air question

    M1602.2 Prohibited sources.

    Outdoor and return air for a
    forced-air heating or cooling system shall not be taken from the
    following locations:
    1.
    2.
    3. A room or space, the volume of which is less than 25 percent
    of the entire volume served by such system.
    STOP You do not need to go any futher
    Where connected by a permanent opening having an area sized
    in accordance with ACCA Manual D, adjoining rooms
    or spaces shall be considered as a single room or space
    for the purpose of determining the volume of such rooms
    or spaces.

    5. A room or space containing a fuel-burning appliance
    where such room or space serves as the sole source of
    return air.
    Exceptions:
    1. The fuel-burning appliance is a direct-vent
    appliance or an appliance not requiring a vent in
    accordance with Section M1801.1 or Chapter 24.
    (NOTE) Definition
    DIRECT-VENT APPLIANCE.
    A fuel-burning appliance
    with a sealed combustion system that draws all air for combustion
    from the outside atmosphere and discharges all flue gases
    to the outside atmosphere.

    (I don't think a FP has a sealed combustion system.)

    2. The room or space complies with the following
    requirements:
    2.1. The return air shall be taken from a
    room or space having a volume exceeding
    exceeding 1 cubic foot for each 10 Btu/h (9.6
    L/W) of combined input rating of all
    fuel-burning appliances therein.
    2.2. The volume of supply air discharged
    back into the same space shall be
    approximately equal to the volume of
    return air taken from the space.
    2.3. Return-air inlets shall not be located
    within 10 feet (3048 mm) of any appliance
    firebox or draft hood in the same
    room or space.
    3. Rooms or spaces containing solid-fuel burning
    appliances, provided that return-air inlets are
    located not less than 10 feet (3048 mm) from
    the firebox of such appliances.


    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

  5. #5
    Join Date
    Mar 2007
    Location
    Western Montana
    Posts
    261

    Default Re: Yet another return air question

    Small point for clarification to avoid confusion.
    Return air is being drawn from the living room through the vent opening in the stairway wall. I took the previously attached pic after I crawled through the return vent opening into the wall cavity under the staircase.

    The fireplace is a direct vent appliance. The exhaust vent also supplies the combustion air supply. http://www.fireplacesnow.com/pdf/ZDV...s_Kingsman.pdf.


  6. #6
    ray jackson's Avatar
    ray jackson Guest

    Default Re: Yet another return air question

    If the fireplace uses type B vent, then it cannot pass through any part of the duct system. I would call that cavity the return air can myself.


  7. #7
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
    Posts
    26,252

    Default Re: Yet another return air question

    Way too many things wrong in that photo to begin to list (Rick duly listed some of them), but let's just say that installing a duct from that hole for the duct to the other hole for the return, properly connected and sealed of course, will ONLY solve those issues related to being in a return air plenum (which is MANY issues, but I say ONLY as that correct will not address the protection of the underside of the stairs, the fireblocking at the stair stringers, etc.).

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

  8. #8
    Join Date
    Jul 2009
    Location
    Cincinnati area
    Posts
    34

    Default Re: Yet another return air question

    I am going to come at this from a different angle. The installation is poor to begin with, as are so many return air systems. The original intent, as I read the post, was to pull air from the next room, rather than from this "plenum". With this installation, who knows where the return air is coming from. The return air duct puts the whole "plenum" under negative pressure, which means that air would be pulled in from wherever, unless every leak in the plenum is sealed. The design sacrifices the efficiency of the heating and air conditioning system because only a portion of the air would come from where it was intended. Basically, the installer was trying to save a few bucks. Rather than installing an extra length of ductwork to the return grille in the wall. Who would ever know, right? You could call it just from that standpoint.


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