Shortening main duct run
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  1. #1
    Question: My main duct running from my HVAC unit runs right up to the bottom of my stairs. I want to shorten it so people don't have to duck when walking down the stairs to my finished basement.

    Ok, I took the end piece off, no problem. Yet, looks like I'll have to do some bends to get it back on once I shorten the rectangular piece. Is there a special tool to do bend the end piece so I can put the cap back on?

    Thanks

  2. #2
    Join Date
    Mar 2004
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    SE Michigan
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    Use your teeth.
    "Politicians are the lowest form of life on Earth. Liberal Democrats are the lowest form of politician"

    - General George S. Patton

  3. #3
    Join Date
    Apr 2004
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    yeah, there is. Its a folding tool and tongs. Together they cost as much as just calling a local contractor to do it.

    You might want to know, there is a reason the duct extends past the last run. Messing with that may just mess up the duct static.

  4. #4
    Shortening it 5 inches will cause a 'static' problem?? If a non professional can't do this, then there is nothing they can do.

    The extra 5 inches will be a world of difference for the stairs.

  5. #5
    Join Date
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    Office and warehouse in both Crystal River & New Port Richey ,FL
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    Originally posted by bucks_2002
    Shortening it 5 inches will cause a 'static' problem?? If a non professional can't do this, then there is nothing they can do.

    The extra 5 inches will be a world of difference for the stairs.

    How many inches from the current end of the duct back to the last branch run??

  6. #6
    About 8 inches to the next run.

  7. #7
    Join Date
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    Originally posted by bucks_2002
    About 8 inches to the next run.

    Next run or last run?


    Is this correct?From the last run/branch ,to the end of the trunk, was 8" and you want to reduce it to 3".

    [Edited by dash on 04-04-2005 at 02:40 PM]

  8. #8
    Last run. New house. Furnace is 2 years old.

  9. #9
    Yes, I want to reduce the main duct by 5" and leave a couple of inches from the last run.

    Yea, na

  10. #10
    Join Date
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    Many here will disagree,but it may not be a problem.

    It's common practice,to have the trunk extend well beyond the last branch,and many believe this is needed to turn the air ,reduce static(resistance to air flow),prevent too much air flow in the last branch,I've heard all these opinions.

    It was the way I was taught in the field early on,but I've never heard it in a classroom.

    I find nothing to support this in Manual D,The Authority residential duct design.In fact drawing in Man. D often show the last branch very close to the end of the trunk.

    So at the least be aware,their is a possibilty that the current air flow to the last branch may be effected.You could remove the end cap,and "plug" the duct,at the point you plan to cut it,and test the air flow(feel) for yourself.

  11. #11
    Ok thanks. Good suggestion on the test. If it is a problem, my father in law will just have to bend down when enetering the man room.

    Where can I get the tool to put the cap back on? The tool to bend the ends so the cap will slip back on. The dudes at Home Depot are clueless.

  12. #12
    Join Date
    Apr 2004
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    7,680
    Its not that it will affect the last run, it will affect total system static. The last run in this case may actually see an increase in airflow but the total system static may drop as a result which may affect airflow to other runs. There is no promise that it will affect it like adding a run out of the end of the duct would but as Dash said, try it by blocking it back for a few days. I just thought I would point it out.

    And BTW, a professional would be able to move the last run if he needed to.

    I said it May.... Dash said it May not... No telling without looking at it. (May is not diffinative)

  13. #13
    Join Date
    Jan 2005
    Posts
    152
    Here's a PIC of the end of one of my duct runs.

    I know there's do DIY here, but I'm just stating what I've done. I've cut the end off this run, and I'm putting in a 45-degree bend from the main line, to the line dissapearing off the top of the picture. The small 5" round going to the left will be cut off & capped; it goes to a tiny bathroom.

    I'm counting on this providing MUCH more airflow to the 15' of duct that connects to the line that dissapears off the top of the pic. I suffer from v. poor airflow in this room; not meeting CFM requirements..
    -Alex

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