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  1. #1
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    Default Flue pipe turned downward

    Gas furnace flue pipe turns downward before entering chimney. Unit has a combustion blower and is located in the crawlspace. I would think that this would not be allowed.

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  2. #2
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    Default Re: Flue pipe turned downward

    Quote Originally Posted by Trent Tarter View Post
    Gas furnace flue pipe turns downward before entering chimney. Unit has a combustion blower and is located in the crawlspace. I would think that this would not be allowed.
    Needs to have a positive rise from start to end. Is there a metal flue pipe in that chimney as well?

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

  3. #3
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    Default Re: Flue pipe turned downward

    That's what I thought just wanted to make shure, and yes the flue pipe goes all the way up chimney.


  4. #4
    A.D. Miller's Avatar
    A.D. Miller Guest

    Default Re: Flue pipe turned downward

    Quote Originally Posted by Trent Tarter View Post
    Gas furnace flue pipe turns downward before entering chimney. Unit has a combustion blower and is located in the crawlspace. I would think that this would not be allowed.
    TT: From Duravent:

    6. Slope.
    If the venting system contains
    lateral (horizontal) components, they shall be
    positioned so they have an upwards slope
    away from the appliance of not less than
    1/4-inch rise per foot of run. (Horizontal
    vent installed in attics, unconditioned area, or

    between floors have further restrictions, please
    consult your local building codes for specific
    limitations.)

    From IRC:
    G2427.10.8 (503.10.8) Slope.
    A vent connector shall be
    installed without dips or sags and shall slope upward toward
    the vent or chimney at least
    1/4 inch per foot (21 mm/m).

    Exception:
    Vent connectors attached to a mechanical draft
    system installed in accordance with the manufacturers’
    instructions.

    The ideal chimney or vent configuration is a totally vertical
    system, even though it is not always practical.
    This section requires all portions of a chimney or vent
    connector to rise vertically a minimum of a
    1/4 inch per
    each foot (21 mm/m) of its horizontal length. The connector
    slope is intended to induce the flow of flue
    gases using the natural buoyancy of the hot gases.
    Connector slope can promote the priming of a cold
    venting system and can partially compensate for short
    connector vertical rise. Low points, dips and sags
    could also trap condensate and accelerate corrosion
    of the connector. The exception allows connectors
    without slope where connected to mechanical draft
    systems because the connector is on the negative
    pressure (inlet) side of the exhauster and slope would
    provide no benefit.




  5. #5
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    Default Re: Flue pipe turned downward

    Isn't that single-wall? If so, not allowed in crawlspace, right?
    It also doesn't appear to be properly supported.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
    www.ArnoldHomeInspections.com

  6. #6
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    Default Re: Flue pipe turned downward

    Not to mention the clearance to combustible and being supported by a rock...


  7. #7
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    Default Re: Flue pipe turned downward

    Quote Originally Posted by John Arnold View Post
    Isn't that single-wall? If so, not allowed in crawlspace, right?
    It also doesn't appear to be properly supported.
    Quote Originally Posted by neal lewis View Post
    Not to mention the clearance to combustible and being supported by a rock...
    All the above, and ANY gravity flow vent is required to be sloped UPward at 1/4" per foot slope - as Aaron noted for Type B Gas Vent, applies to ALL gravity flow vents.

    To my limited knowledge on power vents and direct vents, even those PVC vents are required to be vertical or horizontal sections sloped 1/4" per foot UPward.

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

  8. #8
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    Default Re: Flue pipe turned downward

    Quote Originally Posted by Jerry Peck View Post
    ...
    To my limited knowledge on power vents and direct vents, even those PVC vents are required to be vertical or horizontal sections sloped 1/4" per foot UPward.
    Yes, although for a different reason. It's to get the nasty condensate to drain back to the unit rather than drip outside on the family dog.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
    www.ArnoldHomeInspections.com

  9. #9
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    Default Re: Flue pipe turned downward

    Quote Originally Posted by John Arnold View Post
    Yes, although for a different reason. It's to get the nasty condensate to drain back to the unit rather than drip outside on the family dog.
    I was sure that was the reason (except the dog part ), but I was not 100% sure that applicable to all, just r-e-a-l sure it was.

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

  10. #10
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    Default Re: Flue pipe turned downward

    If that furnace has a fan assisted exhaust does the pitch still play in?

    Mike Schulz License 393
    Affordable Home Inspections
    www.houseinspections.com

  11. #11
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    Default Re: Flue pipe turned downward

    With fan assisted there would be positive pressure in the vent - a vent that is not sealed/ designed against leakage.

    Eric Barker, ACI
    Lake Barrington, IL

  12. #12
    ed ferraioli's Avatar
    ed ferraioli Guest

    Default Re: Flue pipe turned downward

    The vent appears to be to long of a run with 2 elbow -- 30 ft max -each elbow acounts for 10 ft


  13. #13
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    Default Re: Flue pipe turned downward

    Quote Originally Posted by ed ferraioli View Post
    The vent appears to be to long of a run with 2 elbow -- 30 ft max -each elbow acounts for 10 ft
    Ed,

    Do you have documentation which states the above?

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

  14. #14
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    Default Re: Flue pipe turned downward

    Quote Originally Posted by John Arnold View Post
    Yes, although for a different reason. It's to get the nasty condensate to drain back to the unit rather than drip outside on the family dog.
    Reason I have heard was to prevent ice blockage at the end of the vent opening. Probably not good for the dog either!


  15. #15
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    Default Re: Flue pipe turned downward

    Quote Originally Posted by Vern Heiler View Post
    Reason I have heard was to prevent ice blockage at the end of the vent opening. Probably not good for the dog either!
    Yes, although for a different reason. It's to get the nasty condensate to drain back to the unit rather than drip outside on the family dog.
    And it runs back to the unit into a condensate pump or gravity 3/4 pvc and plumbed back outside again for that dog...........

    Mike Schulz License 393
    Affordable Home Inspections
    www.houseinspections.com

  16. #16
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    Cool more Smart Smoke venting

    Cat IV is usually listed with the vent pitched to drain back towards the appliance. Pitching it towards the termination invited ice blockages as does a flat spot. On long horizontal runs in cold regions, this can really become a problem.

    Actually, a fan assisted cat. I gas furnace is still considered negative vent pressure venting. Sure, when it first cycles on there is a short term pressurization of the portion of the vent closest to the appliance collar. But, after a minute, there *should* be enough heat in the stack to generate lift and create a draft or neg. vent pressure. That's why single walled connector and B-vent as still approved with these appliances. The joke is, these appliances are tested with a 5ft vent in the lab.

    If you have leaks in pvc venting, you'll usually see a divot in the concrete where the concentrated acidic condensate is eating up the concrete floor. You can also test joints with a chemical smoke puffer and combustion analyzer.

    To the pics from the OP: why didn't the installer punch through the right hand side of this chimney higher up, use B-vent for a 1" clearance with proper slope and req. in unconditioned space, properly supported? I know, rhetorical question.....

    Trent, I'd be careful with your terminology. A 'combustion blower' might describe a positive pressure combustion chamber. FYI, you cannot power vent out Cat I gas & oil but you can power suck it out at the wall to maintain negative vent pressure.

    Bob

    Keep the fire in the fireplace.

  17. #17
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    Default Re: Flue pipe turned downward

    FYI, you cannot power vent out Cat I gas & oil but you can power suck it out at the wall to maintain negative vent pressure.
    Had one on mine that was mounted to suck it out at the foundation wall made by Field Controls. Never gave a thought why it was that way. Good post Bob.... Thanks

    Mike Schulz License 393
    Affordable Home Inspections
    www.houseinspections.com

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