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Thread: Fresh Air Intake Obstruction

  1. #1
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    Confused Fresh Air Intake Obstruction

    Hello!
    I am a retired mechanical engineer and now a part time Handyman.

    I have a residential client that is complaining about a cold spot on their first floor kitchen approximately 6 feet from an exterior wall. Big house.
    Beneath that floor space is a fresh air intake for the utility room. The intake is 7 inches in diameter, flexible, and is insulated.

    I agreed to take a look at their vents and noted two items:

    1. The air intake has a significant restriction in it of about 50 percent as it enters the ceiling joist space from the furnace / utility room.
    2. There appears to be a second strange connection and restriction within about 6 feet of the exterior wall. It appears that the air intake was broken / interrupted by a ceiling joist that blocks over half of the 7 inch diameter. Please see attached picture.

    Is this against code? If so, what code? Is it safe?
    Should the homeowner take corrective action?

    Thanks very much for your inputs folks. Very much appreciated!
    Attached Images Attached Images  

  2. #2
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    As a tech, please ask your questions here in the "Tech to Tech Chat- Residential" forum. The "AOP Residential HVAC" forum is for homeowners to ask questions.

    Please take note of this new location as the "Moved" icon in the other forum will only last a day.
    Instead of learning the tricks of the trade, learn the trade.

  3. #3
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    Quote Originally Posted by ChanHandyman View Post

    Is this against code? If so, what code? Is it safe?
    Should the homeowner take corrective action?

    Thanks very much for your inputs folks. Very much appreciated!
    Is this a "combustion air" pipe for a mechanical room due to the fact the room is a "confined space" (too small for the appliances within the room)?
    Instead of learning the tricks of the trade, learn the trade.

  4. #4
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    Thread Starter
    Hi Rundawg,
    Thank you for answering my question. Sorry for wrong post area. New to site.

    Yes, the intake runs to a mechanical room shared by a furnace and water heater.

    Best,
    ChanHandyman

  5. #5
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    Quote Originally Posted by ChanHandyman View Post
    Yes, the intake runs to a mechanical room shared by a furnace and water heater.
    An Unconfined Space is one where you have a minimum volume of 50 cubic feet (cf) per 1000 btuh input of all appliances in the space.

    A Confined Space is one in which the volume is less than 50 cf per 1000 btuh input.

    The national code states, that if you have confined space, you will need to bring air into the space via 2 permanent openings between another space within the structure, or outdoors.

    These openings should have a free area of 1 sq in per 1000 btuh if using inside air, or 1 sq in per 4000 btuh if using outside air.

    Be sure to check local codes for any variations in these guidelines (99.9% of the time, they are the same).

    Now lets move away from the written “Code” and talk the realities of combustion. You can have all the space in the world, and if that space has a negative pressure, you may not have enough combustion air to allow for proper and safe combustion of the appliances within that space.

    This is where a technician trained in combustion analysis, can test the operating appliances under varying conditions to determine not only if there is enough combustion air, but that the appliance is venting properly.
    Instead of learning the tricks of the trade, learn the trade.

  6. #6
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    Thread Starter
    Thank you Rundawg.
    I appreciate your comments.
    Kind Regards.

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