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PVC Concentric Vent Termination

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in THE MAIN WALL
The instructions for several mod-con boilers say to install the combustion air elbow in a PVC concentric vent facing up in a horizontal side wall termination.  The instructions that come with the concentric vent itself, however, say to install the combustion air elbow facing downwards.  Both set of instructions say it is important to follow their installation instructions.  Does anyone know the reason for installing a concentric vent in a particular orientation?  I really do not see where it would make a difference. I feel that it would make sence to orientate the concentric vent to reduce the PVC fittings required.

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  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Really ?!?

    I guess it has been a while since I've had an opportunity to read the installation instructions on a concentric vent.



    Let's think this through.



    If I am in a cold environment, and I put a down turned elbow on ANY exhaust vent, do I create the potential of a HUGE ice sicle hanging off the end of the vent termination? And if I am on an upper floor, with a walk area anywhere around the vent terminus, do I expose myself and all concerned with a potential law suit from said glacier falling off of the vent when it warms up in the spring? To say nothing of the possibility of flue gas recycling...



    If I point it straight up, do I create (again) the possibility of ice forming on the structure and doing the same thing previously pointed out, along with destroying the structure from moisture impingement and acidification of the finished surfaces?



    For me and my money, I and thinking a 45 degree fitting, pointed upward will potentially avoid both of the situations previously addressed.



    I just checked my installation manual for Lochinvar Knight, and I see nothing about up and or down, unless you are referring to the WYE branch that provides combustion air, in which case I would defer to the boiler manufacturers requirements, and I have seen it called out both ways.



    Now that I've re-read your post, I realize you ARE talking combustion air, but your use of the term elbow threw me off. The reason for having it up is to avoid pulling in rain into the combustion vestibule of the appliance. Sorry for the long diatribe, but I do have some serious issues with the ice that forms on these terminuses.



    HTH



    ME

    There was an error rendering this rich post.

  • Devan
    Devan Member Posts: 138
    edited December 2009
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    concentric

    I'm confused by what you mean and not understanding the question.If not using a concentric , then you are using elbows with two seperate terminations, of which a manual may tell you to put a elbow facing down.A concentric would be one of those pipes within a pipe kits, and can be install straight up or horizontal, with a hood attached, no way to put an elbow on at termination.
  • TomS
    TomS Member Posts: 62
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    PVC Concentric Vent Termination

    Thanks for the replies.  Thats great that you showed a picture of the concentric vent.  This is the same picture that comes with the instructions for the concentric vent.  My concern is with the left side of the concentric vent where it shows the leg for the intake air facing downward.  In the instructions for the Knight they show the leg for the intake air facing upwards.  There is also a note that says: "IMPORTANT:  Intake leg must be facing up" This is shown on page 23 of the Knight installation and operation manual.  My question is why does it make a difference, and why are there two different instructions given for the same thing.
  • HDE_2
    HDE_2 Member Posts: 140
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    Oh yes the controversy

    The idea of having the 45 degree fresh air intake angled up is to protect the appliance from being the receiving end of moisture draining back to it from condensation and melting snow or rain drawn in. However if turned up and the concentric unit is pitched backwards, the concentric vent assembly collector becomes a collector trapping the moisture.

    Both arguments have been around and I don't think the sole-source manufacturer of the units communicates well with all the OEM's.

    My take is to leave the FA intake 45'd wye turned down,and assure that the concentric vent assembly pitches back towards the outside to allow proper draining.
  • Rich_L
    Rich_L Member Posts: 81
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    Up or Down?

    OK, playing devil's advocate here, if we should have the wye pointing upwards to prevent moisture from being drawn as some have advocated, what prevents this moisture from entering the boiler on a vertical vent termination?

    Merry Christmas to all,

    Rich L
  • TomS
    TomS Member Posts: 62
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    Up or Down

    Good point.  Then too it does not have to be either up or down - the vent can be rotated at any angle between up or down.  I think that the orientation of the vent may make more sense to position it to reduce the fittings necessary for installation. The main problem of course is that two complete opposite instructions are given.  So much for following directions!
  • HDE_2
    HDE_2 Member Posts: 140
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    Rich

    While snowdust will still be a small issue, fortunately it doesnt rain up yet.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    Follow the boiler manufacturers instructions...

    THey are the ones holding the bag of liability in this situation. And they are also the ones backing the warranty.



    I can see arguments both ways regarding pitch. If it is pitched outward, above the Mason-Dixon line, you are guaranteed to have major ice buildup below the vent termination...



    Arguments both ways, but bottom line, follow the boiler manufacturers instructions if you want to maintain a warranty.



    ME

    There was an error rendering this rich post.

  • TomS
    TomS Member Posts: 62
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    Mark

    Mark, I hear you, but this is directly from the instructions of the Concentric vent:

    "Follow the furnace installation instructions for locating the furnace, clearances, operation and safety procedures. Use these instructions for installation of the concentric vent termination kit"
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
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    If in doubt...

    Call the appliance manufacturer and run it by them.



    The building official is going to defer to the boiler manufacturers instructions. They are the ones providing it as an "approved" methodology to their equipment.



    Remember, most boiler manufacturers have a staff of lawyers on hand reviewing all technical data prior to its being released to the public. For good reason.



    ME

    There was an error rendering this rich post.

  • rich pickering
    rich pickering Member Posts: 277
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    problems with concentrics

    One problem with concentrics depends on your climate.  If you have an appliance firing at less than about 30,000 btuh, and an outdoor temp of less than -26, and no wind, you get recirculation of the exhaust because the ventor doesn't provide enough velocity for the gases.

    Thaw out the frost, and it will run back to the boiler, or collect in the pipe and turn to ice.

    Had a 500,000 boiler vented as a 2 pipe with about 2 feet of seperation.  On minimum fire, the 3" intake frosted over in less than 2 hours. 
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