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  1. #1
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    Question HVAV proximity to furnace venting

    Attachment 23571Can anyone tell me the proximity of intake/exhaust of a condensing furnace from HVAC?

    I cant find a code for this......

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  2. #2
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    Default Re: HVAV proximity to furnace venting

    I recently had one that terminated over the AC unit and this is what I used. I don't think it applies in your situation but it will give you starting point.
    Look in the IRC at the same para numbers.

    MI Res Code 2006:

    G2427.8(503.8) Venting system termination location. The

    locationof venting system terminations shall comply with the

    following(see Appendix C):

    .

    3.The vent terminal of a direct-vent appliance with an

    inputof 10,000 Btu per hour (3 kW) or less shall be

    locatedat least 6 inches (152 mm) from any air opening

    intoa building, and such an appliance with an input over

    10,000Btu per hour (3 kW) but not over 50,000 Btu per

    hour(14.7 kW) shall be installed with a 9-inch (230 mm)

    venttermination clearance, and an appliance with an

    inputover 50,000 Btu/h (14.7 kW) shall have at least a

    12-inch (305 mm) vent termination clearance. The bottom

    ofthe vent terminal and the air intake shall be

    locatedat least 12 inches (305 mm) above grade.


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  3. #3
    Darrel Hood's Avatar
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    Default Re: HVAV proximity to furnace venting

    Why does it matter? They won't be operating simultaneously.


  4. #4
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    Default Re: HVAC proximity to furnace venting

    Different question:
    - What kind of wiring is that to/from the disconnects?

    Looks like old cloth covered NM cable ... and it is outside, and the clamps at the bottom of the disconnects look like NM cable clamps.

    Add to that the disconnects appear to be behind the a/c condenser unit, which is blocking the required safe working space in front of the disconnects.

    Jerry Peck, Construction / Litigation Consultant
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  5. #5
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    Default Re: HVAV proximity to furnace venting

    Another consideration is that the exhaust gases from the combustion unit will be corrosive and may affect the cooling fins of the a/c unit.


  6. #6
    Darrel Hood's Avatar
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    Default Re: HVAV proximity to furnace venting

    Rick,
    That code reference is for clearance for an air inlet to the building. An air conditioning condenser unit is not an air inlet.


  7. #7
    Robert Schenck's Avatar
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    Default Re: HVAV proximity to furnace venting

    Quote: Why does it matter? They won't be operating simultaneously.

    Darrel (Hood), .... correct me if I'm wrong and if I am wrong, please (anyone) explain to me how a condensing furnace input / output air does not operate simultaneously ? A furnace needs constant air input for combustion ,,, that is a fact as I know it. Now - with constant air input, there is a constant exhaust being produced ( as long is there is a need for it - per the thermostat). Constant Air In + Constant Air Out = Simultaneous. That's my story and I'm sticking to it


  8. #8
    Robert Schenck's Avatar
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    Default Re: HVAV proximity to furnace venting

    Darrel - Never mind. I read Barry's post the wrong way. I thought you meant the intake / output of the furnace would not operate at the same time. Duh me


  9. #9
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    Red face Re: HVAV proximity to furnace venting

    The furnace is LP gas. The LP tanks are the required 10 feet + from the HVAC. One unit is a heat pump, the other is A/C. The Heat pump and furnace will operate simultaneously during the heating season.

    I don't know if there is a code requirement for for clearance.

    Theoretically the gas furnace will consume ALL the LP before the combustion by products are mechanically vented.

    However is there the possibility of incomplete combustion expelling some amount of LP that might be ignited by the electrical components of the HVAC units?


  10. #10
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    Cool Re: HVAV proximity to furnace venting

    Jerry,

    NM cable NOT cloth covered. House built in 2004.

    Improper box location noted in report with the box NOT having the appropriate clearance side to side and proper front clearance.

    I write almost every one in our area. Techs here set the boxes and put the units directly in front. I guess they are not worried about being electrocuted.....

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  11. #11
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    Default Re: HVAC proximity to furnace venting

    Quote Originally Posted by Barry Lewis View Post
    NM cable NOT cloth covered. House built in 2004.

    And the dryer vent right back there too.

    NM cable is not allowed to be used outside.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
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  12. #12
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    Default Re: HVAV proximity to furnace venting

    Yep, dryer vent right there to clog up the back side of the condenser coil. More revenue for the HVAC tech.

    UF nm cable is allowed outside here for these installations. Almost NEVER see water tight flex conduit installations.

    As a matter of fact, if protected from the elements, regular nm is allowed with certain height restrictions on exterior installations.

    I don't argue with the code enforcement officials here.


  13. #13
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    Default Re: HVAC proximity to furnace venting

    Quote Originally Posted by Barry Lewis View Post
    UF nm cable is allowed outside here for these installations.
    UF and NM are two different animals ... somewhat related to each other, but not closely related, more like distant cousins at best.

    As a matter of fact, if protected from the elements, regular nm is allowed with certain height restrictions on exterior installations.
    Nope.

    Not supposed to be used outside at all. NM cable can come through the wall and terminate in a junction box, but don't try to push it past there as it is not supposed to be run outside or even in conduit outside ... not at any height.

    Jerry Peck, Construction / Litigation Consultant
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  14. #14
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    Default Re: HVAV proximity to furnace venting

    Jerry, non-metalic shielded cable and underground feeder cable are not the same thing. Yes I kinda know that.

    As for the nm run outside....maybe the NEC does not allow it but in some cases it is allowed here. At least my master electrician, with 45 years of experience in residential and commercial work in Virginia and West Virginia, says it is compliant in certain applications. He knows the codes that apply in our area. I do trust his opinion. If I have an electrical question he is my go to guy.

    Whenever I see nm outside I recommend it be shielded by a conduit retrofit.


  15. #15
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    Default Re: HVAC proximity to furnace venting

    Quote Originally Posted by Barry Lewis View Post
    As for the nm run outside....maybe the NEC does not allow it but in some cases it is allowed here. At least my master electrician, with 45 years of experience in residential and commercial work in Virginia and West Virginia, says it is compliant in certain applications. He knows the codes that apply in our area. I do trust his opinion. If I have an electrical question he is my go to guy.
    Find out if the NEC is applicable in your area, and, if so, are there any amendments to it. If no amendments, your electrician is wrong (we all make mistakes).

    If there are amendments which allow for NM cable to be used outside, have him give you the code which allows for it (remember, we all make mistakes ).

    I am eagerly awaiting that code section which allows NM cable to be used outside.

    By the way, NM cable is nonmetallic sheathed cable, not nonmetallic shielded cable.

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