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  1. #1
    Jerome W. Young's Avatar
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    Default gas water heater in sealed garage closet

    The gas water heater was installed in a weather stripped closet located in the garage. The closet is supplied with an a/c vent and a fresh air intake- running through the attic to the soffit. Can you have the a/c supply and the gas water heater and fresh air intake in the same room?

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  2. #2
    A.D. Miller's Avatar
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    Default Re: gas water heater in sealed garage closet

    Quote Originally Posted by Jerome W. Young View Post
    The gas water heater was installed in a weather stripped closet located in the garage. The closet is supplied with an a/c vent and a fresh air intake- running through the attic to the soffit. Can you have the a/c supply and the gas water heater and fresh air intake in the same room?
    JY: Are you certain that the supply register was actually connected to a duct? Often I see these used in place of proper sheet metal ducts, which are not in evidence on this installation.


  3. #3
    Jerome W. Young's Avatar
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    Default Re: gas water heater in sealed garage closet

    the supply duct was connected to the a/c duct work and the fresh air intake was vented to the exterior soffit.


  4. #4
    A.D. Miller's Avatar
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    Default Re: gas water heater in sealed garage closet

    Quote Originally Posted by Jerome W. Young View Post
    the supply duct was connected to the a/c duct work and the fresh air intake was vented to the exterior soffit.
    JY: My opinion, and I am certain it will be summarily overturned by the resident forum deities, there is no prohibition to the presence of the supply register, though a pointless installation, perhaps even counterproductive.

    If that is the only combustion air opening you have adjacent to it, it certainly does not have sufficient net-free area necessary to satisfy the demand of the unit.


  5. #5
    Jerry Peck's Avatar
    Jerry Peck is online now Member
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    Default Re: gas water heater in sealed garage closet

    Jerome,

    Here are a few of the problems as I see them:
    - There is no prohibition to having that supply in that room.
    - HOWEVER ... every room with a supply also needs a return. Which is (thankfully) not installed.
    - The supply air without a return will pressurize that small room.
    - The combustion air vent now simply becomes an exhaust path for the pressurized conditioned air to go directly to the outdoors.
    - The supply pressurizing that small room may well create drafting problems for that water heater.
    - When the a/c system is *not* operating that supply duct now become an air duct passage for transferring air back-and-forth between that room and the rest of the house.
    - The required combustion air *IS NOT* provided for in that one duct to the exterior.

    That is a start of the concerns I would have.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  6. #6
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    Default Re: gas water heater in sealed garage closet

    I'd look REAL close before calling that problem. You REALLY need to be sure that the supply grill was actually connected to the ductwork.

    I often see water heaters in small closets with what looks like a supply register on the ceiling and a 6 inch pipe down to near the floor area.

    When I look at these in the attic, both of them have six inch pipes coming up thru the insulation and stopping.

    The register is just the high vent and the six inch pipe near the floor the low vent.

    You'd have to have a dork of an HVAC installer, or an "unaware" homeowner to connect a duct to that register.

    Just be sure of what you actually saw in the attic over that closet.


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  7. #7
    Bob Harper's Avatar
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    Cool Re: gas water heater in sealed garage closet

    Good points by all (yes, including you Aaron!)

    To follow up on Jerry's point about pressurization:

    IF and I mean IF that supply is indeed connected then several things to consider. The room is a box with one hole in under pressure and two holes out under passive exfiltration. Now, at the velocities and CFM of a typical branch supply, it can far exceed the WH exhaust. So, where does it all go? Path of least resistance. Some will try to squeeze out that passive MUA intake back towards the soffit and some through the draft hood. If that happens, you get:
    -inadequate MUA
    -curtain effect at the draft hood in effect blocking exhaust of the WH. It can vent out the bottom then shoot out the MUA intake or vent. Only due to the rapidly reducing 02 supply, you get incomplete combustion and CO. Now, I see what appears to be some sort of open panel in the wall. Since the walls are not hermetically sealed, some products of combustion will be forced into the adjoining spaces.

    This is wrong on so many levels it's like where to start. Heck, if you supply into a room, it needs a return ( except kitchens and bathrooms) as JP pointed out. That means an imbalance in the duct system. You are sucking air out of one space, pumping it into another with no return so the spaces with returns can depressurize. Now, at these sizes, it may not have that much effect or it might----you need testing to tell. You should see it in the ESP and return SP. Of course, this effects of TD of the furnace/ AC, too. More cause and effect. I would also want to test that supply with a flow hood to know exactly what's coming into that closet. If you inspect the seams of the walls, you'll see dust bunnies collecting at exfiltration points to indicate pressurization and paths of least resistance. I'm sure that weatherstripping has some breaches in it.

    Is that WH on an 18" platform or FVIR?

    Any other support for that B-vent? I know how stiff those listed slinkies are but still, if the firestop support gives way, you're toast.

    That register simply causes the supply to derate 25%.

    Keep the fire in the fireplace.

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