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Venting a Mod Con

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Getting very close to changing out the old boiler for the new. Side venting is not an option. My hope is to use the existing 7" diameter b-vent as a chase for both the vent and intake, but obviously this is a close fit for 3" PVC.

If they both fit down the old chimney, is it OK if they are in contact with each other and the old chimney? My new Knight and I want to know. Concerns would be expansion and contraction noises and any code concerns.

Thanks,

Larry

Comments

  • hot_rod
    hot_rod Member Posts: 22,144
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    Do you need 3\"?

    The new Knight wall hung 50, 80, and 105K vent with 2".

    Two 3" inside a 7 will be a tight fit. Hope there aren't any offsets or screws sticking in :)

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    no offsets

    but I'm sure that any screws sticking in will be in the worst spots! If the wall mounts vent with 2", do you think the factory will allow 2" for a floor model (80M)? Unfortunately, I don't have a good wall space for one. Are they even out yet.

    Thanks,

    Larry
  • hot_rod
    hot_rod Member Posts: 22,144
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    Maybe

    but it probably has more to do with with their listing and approvalsl.

    I know HTP once had a table for combining a pair of 1-1/2" together. This allowed you to replace hydro pulses with Munchkin.

    The actual connection on the Knight intake side is 2". They use a 2X3 increaser fitting at the boiler.

    hot rod
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Dr Pepper
    Dr Pepper Member Posts: 38
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    Press the factory for info...

    the installation guide should have that information but to many do not. W-M has a separate booklet, sometimes it's like pulling teeth. Boiler or furnace their is a length in feet and each elbow counts as so-many feet. Most will also list a maximum number of elbows. Also, you want to know exactly what the discharge configuration is, (example: flue straight up 10"+ above the CAI which requires 2 elbows,and must be installed within 4' of each other.)
    Good luck...
  • Floyd_43
    Floyd_43 Member Posts: 5
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    2\" all the way...

    will probably work just derates the boiler which may not be a bad thing.

    Floyd
  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    thank you

    Floyd, Hot Rod and Dr. Pepper, thank you for the perspectives. I hope to hear from the factory with some options, but considering how the boiler is listed and approved, they may be reluctant to step outside of those listings.

    In any event, I'm quite anxious to get this puppy up and running. Before and after pics will follow eventually.

    Larry
  • Tom Hopkins
    Tom Hopkins Member Posts: 554
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    What size boiler?

    Just remember, that the exhaust passing through 2" tubing will be much more audible than with 3" and the boiler itself will be very quiet. This exhaust noise is all dependent on what your real heat loss load is of course. I'm not sure is a 50 is quieter on 3" than 2" at the lower end. You certainly don't want to be hearing it when your indirect is calling, then again maybe you'll like the sound? ;-)

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  • Larry (from OSHA)
    Larry (from OSHA) Member Posts: 717
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    good point

    Robert, that is an interesting tidbit. The boiler is an 80 and I had not really given any thought to that. It may be a moot point, if the factory won't put their blessing on using the 2 inch. I'm hoping to keep the install as easy as possible, but if we need to rip out the existing chimney, I suspect that my contractor will be able to.

    The last I heard from the factory was a suggestion to use cpvc all the way up. I've suggested a few alternatives for them to consider and we'll see what they say.

    Thanks for your thoughts.

    Larry
  • Mitch_5
    Mitch_5 Member Posts: 102
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    I was talking to WM once about a similar project

    they said they were coming up with spec for running a 3" up the chimney and using the chimney itself t pull the combustion air down. Just talk then I have seen no official spec but it is a thought.

    Mitch S.

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  • Perry_3
    Perry_3 Member Posts: 498
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    Vitodens Cocentric Vent...

    Solved this problem long ago...

    I should also note; that for side venting I had to run the vent up into a closet on the first floor and then vent out the side of the house in order to be above normal heavy snow in this area (2 ft above normal snow line).

    I note that I believe I have one of the few houses in the area with a retrofit that actually meets this code requirment.

    Perry
  • Perry_3
    Perry_3 Member Posts: 498
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    Vitodens Cocentric Vent...

    Opps! Double post. Double post.

    :(

    I've deleted text.

    Please disregard.


    Perry
This discussion has been closed.