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  1. #1
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    Default Power Vent Exhaust To Direct Vent Furnace Intake Clearance

    Many of the power vent water heater installation manuals I have reviewed call for the power vent exhaust termination to be 3' above any forced air inlet within 10' horizontally.

    My question is - would the combustion air intake for a direct vent furnace be defined as "a forced air inlet"?

    And if not...what are some examples of "forced air inlets"?

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    Dave Tontarski
    Act in haste....repent in leisure

  2. #2
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    Default Re: Power Vent Exhaust To Direct Vent Furnace Intake Clearance

    Quote Originally Posted by David Tontarski View Post
    Many of the power vent water heater installation manuals I have reviewed call for the power vent exhaust termination to be 3' above any forced air inlet within 10' horizontally.

    My question is - would the combustion air intake for a direct vent furnace be defined as "a forced air inlet"?

    And if not...what are some examples of "forced air inlets"?
    The combustion air intake is not a fresh air intake. A fresh air intake would be something like an HRV, which sucks in fresh air from the outside. This is when the 3/10 rule would apply.
    Healthy Climate Heat Recovery Ventilator (HRV) | Lennox Residential

    Scott Patterson, ACI
    Spring Hill, TN
    www.traceinspections.com

  3. #3
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    Default Re: Power Vent Exhaust To Direct Vent Furnace Intake Clearance

    Quote Originally Posted by Scott Patterson View Post
    The combustion air intake is not a fresh air intake. A fresh air intake would be something like an HRV, which sucks in fresh air from the outside. This is when the 3/10 rule would apply.
    Healthy Climate Heat Recovery Ventilator (HRV) | Lennox Residential
    My question is - would the combustion air intake for a direct vent furnace be defined as "a forced air inlet"?

    The room needs adequate combustion air. The system you are talking about is most probably in the mechanical room. even if not, the room needs combustion air for the appliance.
    Any household appliance thats feed is flammable gas, liquid or liquid under pressure needs combustion air. There would be a direct vent feeding the room or adequate space and the room vented.

    I personally have never seen a direct combustion air feed directly to the appliance at the source of ignition and burn.
    I can imagine many reasons why it is not done that way. Just the intake venting would be a nightmare and space is at a premium in a home. Any blockage restricting air could be damaging and a safety risk. I may be wrong mind you.
    I hope that helps.

    In short the above is a heat recovery system.
    The acronym HRV (Heat Recovery Ventilation) systems was new Peter.
    Thanks.
    I have seen many and refer to the in full text. HRV from now on.

    Last edited by ROBERT YOUNG; 01-27-2014 at 05:21 AM.
    Robert Young's Montreal Home Inspection Services Inc.
    Call (514) 489-1887 or (514) 441-3732
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  4. #4
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    Ormond Beach, Florida
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    Default Re: Power Vent Exhaust To Direct Vent Furnace Intake Clearance

    Quote Originally Posted by ROBERT YOUNG View Post
    My question is - would the combustion air intake for a direct vent furnace be defined as "a forced air inlet"?
    Read the instructions more carefully and I suspect you will read something similar to this from the code: (bold and underlining is mine)
    - Air exhaust openings shall terminate not less than 3 feet (914 mm) from property lines; 3 feet (914 mm) from operable and nonoperable openings into the building and 10 feet (3048 mm) from mechanical air intakes except where the opening is located 3 feet (914 mm) above the air intake.

    A direct vented appliance does not have its combustion air go "into the building" other than being contained in a fully enclosed and sealed duct. Bob Harper can probably state that better.

    Thus the "openings into the building" would not be applicable.

    The second part regarding "mechanical air intakes" is, I believe, intended to indicate 'mechanical air intakes into the building's environmental air', not just a 'mechanical air intake to mechanical equipment for combustion purposes only'.

    If there is a possibility of that air being mixed with the environmental air within the building, then the clearances would apply, however, if the ducts were sealed and the air only went to the mechanical equipment for combustion air and then went back outdoors by way of a sealed exhaust system ... I started to say 'that should be okay', however, even that could affect the combustion of the appliance if the combustion air was gradually but constantly degraded by co-mingling the combustion byproducts with the combustion air ... so I am ending up saying 'the clearances should be maintained'.

    Anyone think of a reason that the clearances would not need to be maintained?

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

  5. #5
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    Default Re: Power Vent Exhaust To Direct Vent Furnace Intake Clearance

    I was mistaken in my interpretation of the question that started the thread. Sorry.

    A direct vented appliance does not have its combustion air go "into the building" other than being contained in a fully enclosed and sealed duct.





    Robert Young's Montreal Home Inspection Services Inc.
    Call (514) 489-1887 or (514) 441-3732
    Our Motto; Putting information where you need it most, "In your hands.

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