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  1. #1
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    Default Single or double wall flue pipe?

    I am having one of those days! I am reviewing pictures from an inspection I performed yesterday.
    I am looking at this one and wondering why I took it.
    It looks like it is single wall pipe coming off the furnace, but I am not sure. Can anyone tell by looking at the picture. Does type b flue always have the thick seam at the ends?
    Also, is the 180 bend permitted. On down the line, the pipe turns 90 degrees up and through the roof.
    This is a newer gas rheem furnace located in an attic.

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  2. #2
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    Default Re: Single or double wall flue pipe?

    Looks like single wall to me. That insulated refrigerant line looks too close to the vent.
    And I'd also be leery of the 180 bend. I've never seen that done.

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  3. #3
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    Default Re: Single or double wall flue pipe?

    You are in WV where the Winter Design Temperature is below 32 degrees F, thus, single wall vents are not allowed outdoors (outside the thermal envelope).

    Additionally, single wall metal pipe vent is not allowed in the attic.

    To my knowledge, that elbow would be permitted in the correct installation, but this is not a correct installation (first and foremost because it is single wall vent and is in the attic and outside the thermal envelope.

    From the 2006 IRC. (underlining is mine)

    - G2427.7.2 (503.7.2) Cold climate. Uninsulated single-wall metal pipe shall not be used outdoors for venting appliances in regions where the 99-percent winter design temperature is below 32ºF (0ºC).

    - G2427.7.6 (503.7.6) Installation.Single-wall metal pipe shall not originate in any unoccupied attic or concealed space and shall not pass through any attic, inside wall, concealed space, or floor. The installation of a single-wall metal pipe through an exterior combustible wall shall comply with Section G2427.10.15. Single-wall metal pipe used for venting an incinerator shall be exposed and readily examinable for its full length and shall have suitable clearances maintained.

    Plus, as John said, that insulation is too close too the vent - single wall vent requires 6" clearance to combustible material.

    Jerry Peck, Construction / Litigation Consultant
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  4. #4
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    Default Re: Single or double wall flue pipe?

    Thanks for your input. I am aware of the requirements and limitations of using single wall pipe. My question was really concerning the indentification of single wall pipe. (by looking at the picture only). This was a very large house (8,000 sq ft) and I had taken lots of pictures and notes and when I was reviewing this particular picture I was trying to remember why I took it. I then questioned whether or not the pipe was single or double wall and was asking if you can always identify double wall pipe by the ends of the pipe.
    Greg

    Greg Jenkins

  5. #5
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    Default Re: Single or double wall flue pipe?

    Yes you can. The dbl wall pipe has an indention that looks like a depressed ring around it! That is where they twist and lock together.




  6. #6
    adkjac's Avatar
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    Default Re: Single or double wall flue pipe?

    if that is the flue, no way is that right.'
    aj


  7. #7
    RANDY NICHOLAS's Avatar
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    Default Re: Single or double wall flue pipe?

    Isn't a 180 bend just a straight pipe or is the new math enforced in 2009 along with the metric system?


  8. #8
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    Default Re: Single or double wall flue pipe?

    Quote Originally Posted by RANDY NICHOLAS View Post
    Isn't a 180 bend just a straight pipe or is the new math ...
    .

    That "new math".

    You know that "new math" stuff where you are going in one direction and make a 'U' turn and go in the other direction?

    Yep, 180 degree turn.

    (I think you are thinking of a 360 degree bend. However, a 360 degree bend is still not a "straight pipe", it just has a loop in it. )

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  9. #9
    Inspector 3500's Avatar
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    Default Re: Single or double wall flue pipe?

    What is the orange cord at the top of the picture?


  10. #10
    Jim Weyenberg's Avatar
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    Default Re: Single or double wall flue pipe?

    Greg,
    Is it possible that 180 bend is for combustion intake air?

    Jim Weyenberg
    HouseMaster Inc.
    WI.


  11. #11
    adkjac's Avatar
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    Default Re: Single or double wall flue pipe?

    Quote Originally Posted by Jim Weyenberg View Post
    Greg,
    Is it possible that 180 bend is for combustion intake air?

    Jim Weyenberg
    HouseMaster Inc.
    WI.
    I second Jim's motion...
    aj


  12. #12
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    Default Re: Single or double wall flue pipe?

    Quote Originally Posted by adkjac View Post
    I second Jim's motion...
    aj

    That looks like a standard Cat 1 appliance. I doubt there's a dedicated combustion air intake for that furnace.


  13. #13
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    Default Re: Single or double wall flue pipe?

    Quote Originally Posted by neal lewis View Post
    That looks like a standard Cat 1 appliance. I doubt there's a dedicated combustion air intake for that furnace.
    Not being a gas furnace guy (I did not see many gas furnaces in South Florida), is a dedicated combustion air intake required for a Cat 1 furnace installed in an attic, which is already considered 'outside the thermal envelope' and which is considered to contain 'outdoor air' because of its ventilation to the outdoors?

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  14. #14
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    Default Re: Single or double wall flue pipe?

    The elbow I see is a 90 Degree In my area a single wall flue is allowed as long as there is 6" from a combustionable material. Insualtion on the sunction line for the condenser may qualify as combustionable material


  15. #15
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    Default Re: Single or double wall flue pipe?

    Quote Originally Posted by Chuck Melocco View Post
    In my area a single wall flue is allowed as long as there is 6" from a combustionable material.

    Even in an attic?

    Jerry Peck, Construction / Litigation Consultant
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  16. #16
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    Default Re: Single or double wall flue pipe?

    Ran across this elsewhere (not an HI board), but felt it was a true classic:



    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  17. #17
    Chuck Jones's Avatar
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    Default Re: Single or double wall flue pipe?

    The furnace is an induced draft 80% efficient unit. The pipe is question is the flue pipe. Combustion air would be brought in via vents in the roof or a gable wall. The picture indicates a single wall pipe as there are no twist lock rings.


  18. #18
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    Default Re: Single or double wall flue pipe?



    (c) Chuck Jones Enterprises

    Meanwhile, I got curious about if/how you patch that properly, and Simpson DuraVent sent me this:

    Attached Files Attached Files
    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  19. #19
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    Default Re: Single or double wall flue pipe?

    Well.... I followed up further with Simpson DuraVent, and was told:

    "If the hole is for any other purpose or size than to test the draft with a probe then the hole is not allowed."

    Likely, every B-Vent manufacturer is going to say something similar, so there is a good chance that if you want to be in compliance with the manufacture's requirements (and thus with code, which incorporated these) that section of B-Vent would have to be replaced.

    Michael Thomas
    Paragon Property Services Inc., Chicago IL
    http://paragoninspects.com

  20. #20
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    Default Re: Single or double wall flue pipe?

    Quote Originally Posted by Greg Jenkins View Post
    Does type b flue always have the thick seam at the ends?
    No. I have some pics from today's inspection. It is a B-vent, but the big seam is not present. This is from the early '70s.

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  21. #21
    Craig Ervin's Avatar
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    Default Re: Single or double wall flue pipe?

    Quote Originally Posted by Inspector 3500 View Post
    What is the orange cord at the top of the picture?
    Looks to be t-stat wire. I also noticed the secondary A-coil drain is pluged.

    To me it looks like the A/C line was run and later they did the furnace vent so that force them to mount like so. The vent should have 90 up and then less then 90 to go back over the furnace and not in front of the access panel


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