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    Return air question

    Return air question

    New postby Marc M on Sun Aug 25, 2013 1:35 am

    Hey Jerry,
    just need clarification. Does this below exception underlined, say that you "can" have a return air near a fireplace etc...?

    2010 CMC 311.3 Prohibited Source. Outside or return air for a heating
    or cooling air system shall not be taken from the following
    locations:


    Exception: Such openings when used for a heating or
    cooling air system in a dwelling unit shall be permitted
    to be reduced to not less than 50 percent of the required area, provided the balance of the required return air is taken from a room or hall having not less than three (3) doors leading to other rooms served by the furnace.
    (5) A closet, bathroom, toilet room, or kitchen.
    (6) From rooms or spaces containing a fuel-burning appliance
    therein.Where such room or space serves as source
    of return air.
    Exceptions:
    (1) This shall not apply to fireplaces, fireplace appliance,
    residential cooking appliance, direct vent
    appliance, enclosed furnaces, and domestic-type
    clothes dryers installed within the room or space
    .
    Marc M
     
    Posts: 173
    Joined: Sat May 09, 2009 10:24 am

    Re: Return air question

    New postby Jerry Peck - Codeman on Sun Aug 25, 2013 11:10 am

    Marc,

    That is an exception to the exception - i.e. Return air is not permitted to be taken from a room or space containing a fuel-burning appliance where the room or space serves as ["a"] source of return air ... unless ...
    - unless the fuel-burning appliance is a direct-vent appliance (makes sense as a direct vent appliance gets all combustion air from outdoors and all combustion by-products are discharged outdoors)
    - unless the fuel-burning appliance is a gravity-type or listed (listed to what?) heating or cooling wall unit (makes sense if it was additionally specified that the 'wall unit was located in that same room or space' and was not allowed to be in some other room - this is 'implied' but not stated)
    - unless the fuel-burning appliance is a blower-type which meets ["all"] the following (makes sense because the room or space exceeds the volume required to make it not confined space; that 75% or more of the supply air is put back in the same room, which indicates that up to 25% of the return air is being replaced by air from outside that room or space; and that the return is located at least 10 ft from the firebox or draft hood)
    - - where the room or space volume exceeds 1 cf for each 10 Btu/h input rating, ["and"]
    - - where the not less than 75% of the supply air is put back in the same room or space the return air was taken from, ["and"]
    - - where return air inlets are not within 10 ft of the appliance firebox or draft diverter in that room or space

    From the 2010 CMC:
    - 311.3 Prohibited Source. Outside or return air for a heating or cooling air system shall not be taken from the following locations:
    - - 1. Closer than ten (10) feet (3,048 mm) from an appliance vent outlet, a vent opening of a plumbing drainage system, or the discharge outlet of an exhaust fan, unless the outlet is three (3) feet (914 mm) above the outside-air-inlet.
    - - 2. Where it is less than ten (10) feet above the surface of any abutting public way, driveway, sidewalk, street, alley or driveway.
    - - 3. A hazardous or insanitary location or a refrigeration machinery room as defined in this code.
    - - 4. From an area, the volume of which is less than 25 percent of the entire volume served by such system, unless there is a permanent opening to an area the volume of which is equal to 25 percent of the entire volume served. 44
    - - - Exception: Such openings when used for a heating or cooling air system in a dwelling unit shall be permitted to be reduced to not less than 50 percent of the required area, provided the balance of the required return air is taken from a room or hall having not less than three (3) doors leading to other rooms served by the furnace.
    - - 5. A closet, bathroom, toilet room, or kitchen.
    - - 6. From rooms or spaces containing a fuel-burning appliance therein. Where such room or space serves as source of return air.
    - - - Exceptions:
    - - - - 1. This shall not apply to fireplaces, fireplace appliance, residential cooking appliance, direct vent appliance, enclosed furnaces, and domestic-type clothes dryers installed within the room or space.
    - - - - 2. This shall not apply to a gravity-type or listed vented wall heating or cooling air system.
    - - - - 3. This shall not apply to a blower-type heating or cooling air system complying with the following requirements:
    - - - - - a. Where the return air is taken from a room or space having a volume exceeding one (1) cubic foot for each ten (10) Btu/h (2.93 W) fuel input rating of all fuel-burning appliances therein.
    - - - - - b. Not less than 75 percent of the supply air is discharged back into the same room or space.
    - - - - - c. Return-air inlets shall not be located within ten (10) feet (3,048 mm) from any appliance firebox or draft diverter in the same enclosed room or confined space.

    Does this below exception underlined, say that you "can" have a return air near a fireplace etc...?


    That exception says 'Yes, you can, but ... only if you meet the requirements listed - which are quite limiting.
    Jerry Peck - CodeMan
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    Re: Return air question

    New postby Marc M on Sun Aug 25, 2013 11:23 am

    Go it, that will work. Detailed as usual...thanks for the help Jerry.
    Marc M
     
    Posts: 173
    Joined: Sat May 09, 2009 10:24 am


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