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Thread: One duct in, Eight ducts out

  1. #1
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    One duct in, Eight ducts out

    Zoned system and customer was complaining upstairs doesn't have good airflow. Of course it doesn't... 14" duct goes into this ductboard box and then 8 ducts distribute out. They should have just setup a reducing trunkline with round pipe... how much more work would that have been... OMG
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    wHen I diE I hOpe gOd haS mErcy oN my SiNful LifE

  2. #2
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    Zoning distribution box... done dozens and dozens of those...
    As long as the air VOLUME going in is sufficient... then the flow out the spider will be fine.
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
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    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *The value of comfort, over the long term; leave economic choices behind!
    Choose your contractor wisely!

  3. #3
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    Thread Starter
    Well it's a 14" flex in but I think there's a mixer of 6" and 8" ducts in the box... I don't think there is enough air velocity to fed all those ducts.

  4. #4
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    Might be enough air going into the distribution box, may not be... have to calculate it.

    Personal opinion: be extra careful of installing the 14" duct carefully: stretched, corners gradual, etc... for good airflow TO the distribution box.
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *The value of comfort, over the long term; leave economic choices behind!
    Choose your contractor wisely!

  5. #5
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    I prefer the term distribution facilitator's

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  7. #6
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    Its a shiny spider!

    14" is about 1000 cfm, so maybe 6 - 6's and 2 - 8's, but your still starved with that setup, unless maybe there's dampers

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  9. #7
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    Quote Originally Posted by RMSG01 View Post
    Its a shiny spider!

    14" is about 1000 cfm, so maybe 6 - 6's and 2 - 8's, but your still starved with that setup, unless maybe there's dampers
    You should also see how long they ran the flex ducts...some sagging... well over the 25 ft... I think they merged in some 2 together. I should have taken a pic of the duct runs.
    wHen I diE I hOpe gOd haS mErcy oN my SiNful LifE

  10. #8
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    Hmmm...

    14", at .5 static, is more like 650-750 CFM's...

    Which does not really leave a lot of air for more than a handful of ducts.

    Assuming that pic has 2 more ducts on the back (total of 8)... then yeah... too many runs off the box.

    ALWAYS do the calculations...
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *The value of comfort, over the long term; leave economic choices behind!
    Choose your contractor wisely!

  11. #9
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    Quote Originally Posted by ga-hvac-tech View Post
    Hmmm...

    14", at .5 static, is more like 650-750 CFM's...

    Which does not really leave a lot of air for more than a handful of ducts.

    Assuming that pic has 2 more ducts on the back (total of 8)... then yeah... too many runs off the box.

    ALWAYS do the calculations...
    Yeah, I was going off the .10 measurement(recommended for residential), but I am sure flex is less, which definitely makes it less efficient. I was also told, by a guy more savvy than I, if your running less than 25' of flex, go ahead and use the .10 rather than the .05 on the duct calculator, or go somewhere in the middle or a little less than the .10, which left me confused to say the least LOL. but I rarely run flex, so I am accustomed to the metal measurements an sizes anyway. Man after looking at the .05 it is under sized to say the least.

  12. #10
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    Quote Originally Posted by mofotech View Post
    You should also see how long they ran the flex ducts...some sagging... well over the 25 ft... I think they merged in some 2 together. I should have taken a pic of the duct runs.
    I've ran one flex over 25' in my entire career, I went from an 8" to a 6" and it used almost both boxes and seemed to do the trick, but I also ask before doing the run what would be the best way to achieve the outcome wanted.

  13. #11
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    Quote Originally Posted by RMSG01 View Post
    Yeah, I was going off the .10 measurement(recommended for residential), but I am sure flex is less, which definitely makes it less efficient. I was also told, by a guy more savvy than I, if your running less than 25' of flex, go ahead and use the .10 rather than the .05 on the duct calculator, or go somewhere in the middle or a little less than the .10, which left me confused to say the least LOL. but I rarely run flex, so I am accustomed to the metal measurements an sizes anyway. Man after looking at the .05 it is under sized to say the least.
    Quote Originally Posted by RMSG01 View Post
    I've ran one flex over 25' in my entire career, I went from an 8" to a 6" and it used almost both boxes and seemed to do the trick, but I also ask before doing the run what would be the best way to achieve the outcome wanted.
    As I remember... ductulators tend to be rated for 100' runs... so less than one box/tube of flex... is less critical.

    I remember doing that also... 40-something foot run... ran a box of 8", then downsized to 6" for the rest of the run...
    Air velocity at the vent was about the same as the rest of the house... so it worked.
    Another one: boot/register was for a 7" duct... ran 35 ft of 8" flex... corner bedroom... airflow velocity was a little high (not noisy)... and the heat/cooling in that room was seriously improved!

    Airflow... probably the least understood, yet most important thing... in heating and AC.
    GA-HVAC-Tech

    Your comfort, Your way, Everyday!

    GA's basic rules of home heating and AC upgrades:
    *Installation is more important than the brand of equipment
    *The duct system keeps the house comfortable; the equipment only heats and cools (and dehumidifies)
    *The value of comfort, over the long term; leave economic choices behind!
    Choose your contractor wisely!

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