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Concentric vent termination

JL_2
JL_2 Member Posts: 17
Can anyone help with a problem I have never ran into. I am adding a direct vent appliance to an addition and they want the flue to be terminated in a flue/chimney chase next to an existing 8" B-vent for the existing boiler. I want to use a concentric vent and I know all the manuals say you can terminate two concentrics side by side 8" on center and then the next set of two has to be 3 feet away. What if one of those is 8" B-vent? Height and center codes? Thanks for the help!

Comments

  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669
    venting

    Since only one is concentric - Run the new vent pipe up next to the existing 8" B vent. Install another B vent pipe (only at the top), run the new PVC pipe through the new B Vent pipe and out the top of the B vent cap, ( cut a hole in it) terminate the PVC pipe at the same height as the 8" B Vent top. I would make sure that the new B vent cap is at least 18 inches lower than both terminations. Now install another pipe into the chimney chaseway and use the chimney chaseway as your combustion air intake. I have done this before with the local inspectors approval beforehand. Worked great. The new B vent must be at least 1 inch larger that the OD of the PVC vent pipe because the combustion air will be drawn in through the new vent cap and down the chimney chaseway. The bottom of the chimney chaseway needs to be sealed so all of the combustion air comes from outside.
  • Tim McElwain
    Tim McElwain Member Posts: 4,612
    You can't use

    the chimney chase way for combustion air especially with a "B" vent in the chase. "B" vent is not sealed tight and could leak giving you contaminated air.



    Whoever the inspector who approved such a thing is he does not know the code book. If someone dies I wonder if he will show up. I would get him to sign off on such a venture. Or better yet DO NOT GET AIR FOR COMBUSTION EVER FROM A CHIMNEY EVEN IF IT IS NOT BEING USED AS A CHIMNEY ANYMORE!.
  • zacmobile
    zacmobile Member Posts: 211
    concentric

    I don't think he is intending to use the chimney as a combustion air duct, he is using concentric venting which has sealed combustion air in the outer pipe in the same space as a B-vent from another appliance.



    I don't know about the US but in Canada you would need to terminate it 6ft. from any mechanical air inlet to the building, and that includes a vent from any atmospheric appliance.
  • Henry
    Henry Member Posts: 998
    Combustion air etc

    Certain boiler manufacturers allow the installer to use the area around a vent for combusiton air with certain specific drawings in their certified I & O manuals. B149.1 will allow that In Canada. I have passed an amendements for a clause, that does not allow say a Cat1 appliance to vent in the space of the chimney when a Cat 2 or 4 vents through it. It is in the B149.10 code. Basicaly, we don't want cross contamination nor do we want a plastic vent in a Cat 1 chimney. As well one cannot use a chase to vent several apliances. each apliance needs to have its own chase!  
  • Tim McElwain
    Tim McElwain Member Posts: 4,612
    I think I read it correctly:

    Now install another pipe into the chimney chaseway and use the chimney chaseway as your combustion air intake. I have done this before with the local inspectors approval beforehand. Worked great. The new B vent must be at least 1 inch larger that the OD of the PVC vent pipe because the combustion air will be drawn in through the new vent cap and down the chimney chaseway. The bottom of the chimney chaseway needs to be sealed so all of the combustion air comes from outside.

    He is using the air in the chimney/chaseway now as his air for combustion if that is the case you can't do that as there is the potential for cross contamination.



    I would be surprised if the equipment manufacturer allows this on their equipment. I do not always trust the judgement of inspectors as i often have proved them wrong on many code interpretations. 
  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669
    Venting

    B vent is NOT under positive pressure - it is designed to be used in a negative pressure venting only.  You would be sealing the chimney at the bottom and it is a closed combustion appliance. It is legal to use the chimney as a chaseway for the sealed combustion airflow. You can use a vertical chaseway ( chimney ) for multiple venting ducts as long as the chimney is no longer used for venting of unducted gasses.
  • Tim McElwain
    Tim McElwain Member Posts: 4,612
    Steve

    What code is allowing this and what OEM? The fact that the B vent is not a sealed system makes for a potential problem if you lose draft on the B vent and flue gases leak into the chase.



    I am open to learn just need to see code approval and OEM allowing such a HOOK UP.



    EVERY ONE I HAVE SEEN THAT TRIED TO DO THIS IN RI AND MASS WAS NOT APPROVED BY THE INSPECTOR.
  • Tim McElwain
    Tim McElwain Member Posts: 4,612
    Here are my references from

    two different codes.



    National Fuel Gas Code NFPA 54/ANSI Z223.1



     

    12.6.8 Space Surrounding Lining or Vent.

     

     

    12.6.8.1 The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic pipmg installed within a masonry chimney shall not be used to vent another appliance.



     

    Exception: The insertion of  another liner or vent  within the chimney as provided in this code and the liner or vent manufacturer’s instructions.



     

    12.6.8.2 The remaining space surrounding a chimney liner, gas vent, special gas vent, or plastic piping installed within masonry, metal, or factory-built chimney flue shall not be used to supply combustion air.





     

    Exception: Direct vent appliances designed for installation in a solid  fuel-burning fireplace where installed in accordance with the manufacturer’s installation instructions.



     

     

    International Fuel Gas Code





     

    503.5.10 Space surrounding lining or vent. The remain­ing space surrounding a chimney liner, gas vent, special gas vent or plastic piping installed within a masonry chimney flue shall not be used to vent another appliance. The inser­tion of another liner or vent within the chimney as provided in this code and the liner or vent manufacturer's instructions shall not be prohibited. The remaining space surrounding a chimney liner, gas vent, special gas vent or plastic piping installed within masonry, metal or factory-built chimney shall not be used to supply combustion air. Such space shall not be prohibited from supplying combustion air to direct-vent appliances designed for installation in a solid fuel-burning fireplace and installed in accordance with the manufacturer's instal­lation instructions.
  • JL_2
    JL_2 Member Posts: 17
    Response

    Are you saying it is against code to run two or three b-vents in the same chase. On some of these house there might be a huge chimney chase on multiple wings of the house. They are usual five six feet long and two or three feet wide. Sometimes they put a bird cage on top so you don't see the flues. This is just a chase on top of the roof for nothing but looks. I'm not going to pull combustion from inside the chase. The problem here is I want to use a concentric vent due to our cold winters. Two pipe installations fail at this altitude. So how does everyone feel about stubbing out the b-vent 24" above the top of the chase and the concentric 16" above the top of the chase giving it a 8" separation in height. The center to center measurement will be about 15". I am about ready to ditch the concentric and stub out a two pipe, one on top and one on the side of the chase. I talk to the manufacturer and they seemed to only be concerned about PVC and b-vent in the same chase. The radiation from the b-vent could make the PVC brittle over time they said. I just thought I'd check with the pros at heating help. Thanks for everyone's input.
  • Steve Whitbeck
    Steve Whitbeck Member Posts: 669
    edited May 2012
    Tim

    You might want to check the install manuall for Weil McLain boilers. CGs

    the codes don't mean a thing IF the installation manual says it is OK to do something and vice versa.



    Also - How would gasses get into the building if the OTHER appliance is closed combustion.

    If you don't want to use the space around the B vent as a duct for the combustion air then run both PVC pipes up to the top of the chimney and do a concentric vent.
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