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  1. #1
    Join Date
    Feb 2007
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    999

    air flow question

    I have a typical 2 story, 4 bedroom house, which is served by a single HVAC system.

    Air flow upstairs is reasonable with the exception of one bedroom, which is my computer/radio room and serves as a spare bedroom.

    That bedroom and a next door bathroom are each provided with a single 6" run/register. The run to the bedroom is approximately 24' longer than the other. The bathroom has plenty of air and no adjustment of the damper seems to help.

    The runs originate 2' (bedroom) and 3' (bathroom) from the trunk/plenum junction. So far, I haven't been able to find the 'sweet spot' by adjusting the two dampers. I would have thought that the bedroom being first in line, would have the greater air flow. Wrong?

    Might one of those squirel cage duct fans help? Any other suggestions?

    Thanks.

    AM

  2. #2
    Join Date
    Jan 2004
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    Lancaster PA
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    68,090
    Depends on how turbulant the air is where the bedroom taps into the trunk.

    I think before I had a contractor install a booster fan, I would have them switch the bath and bedroom on the takeoffs, to see if that gave more air.
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  3. #3
    Join Date
    Feb 2007
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    999
    Quote Originally Posted by beenthere View Post
    Depends on how turbulant the air is where the bedroom taps into the trunk.
    The 'bedroom' is upstream of the 'bathroom'. As they are close together, wouldn't the air be more turbulent entering the 'bathroom'?

    I think before I had a contractor install a booster fan, I would have them switch the bath and bedroom on the takeoffs, to see if that gave more air.
    I'm trying to visualize how this would go. Would probably have to add a couple of elbows (45's anyway) to those already convoluted runs.

    AM

  4. #4
    Join Date
    Jan 2004
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    Lancaster PA
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    Air tends to move as it wants, not as we think it should.

    Could always have them increase the size going to that bedroom.
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  5. #5
    Join Date
    Jun 2005
    Location
    SW Wisconsin
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    4,989
    Quote Originally Posted by ampulman View Post
    I have a typical 2 story, 4 bedroom house, which is served by a single HVAC system.

    Air flow upstairs is reasonable with the exception of one bedroom, which is my computer/radio room and serves as a spare bedroom.

    That bedroom and a next door bathroom are each provided with a single 6" run/register. The run to the bedroom is approximately 24' longer than the other. The bathroom has plenty of air and no adjustment of the damper seems to help.

    The runs originate 2' (bedroom) and 3' (bathroom) from the trunk/plenum junction. So far, I haven't been able to find the 'sweet spot' by adjusting the two dampers. I would have thought that the bedroom being first in line, would have the greater air flow. Wrong?

    Might one of those squirrel cage duct fans help? Any other suggestions?

    Thanks. AM
    What Return-Air paths do the bedroom & bath on one 6" supply have?

    Are the boot & diffuser combo sized to handle the required airflow.

    Is it a 90-ell 6" top trunk take-off? Some of those types have a pressure drop with an equivalent length of 50' feet.
    Use a large take-off flange on the main trunk that provides a large entry area providing funneling into a 7" duct. A Take-off that will only have an equivalent length of 15' feet, Vs 50' feet.

    If you go with a 7" take-off & 7" rd duct, at least for part of the way, the boot an double diffuser should to be changed to handle the increased amount of CFM.

    The Main Trunk Take-off equivalent lengths, are important to effect efficient airflow.

    Make certain there are ample Return Air paths for those rooms!

  6. #6
    Join Date
    Feb 2007
    Posts
    999
    Quote Originally Posted by udarrell View Post
    What Return-Air paths do the bedroom & bath on one 6" supply have?

    Are the boot & diffuser combo sized to handle the required airflow.
    Both are 'returned' via the central hall single return. I doubt it. Judging by the overall quality of the ductwork (one size fits all).

    Is it a 90-ell 6" top trunk take-off? Some of those types have a pressure drop with an equivalent length of 50' feet.
    Yes

    Use a large take-off flange on the main trunk that provides a large entry area providing funneling into a 7" duct. A Take-off that will only have an equivalent length of 15' feet, Vs 50' feet.
    Will look into it.

    If you go with a 7" take-off & 7" rd duct, at least for part of the way, the boot an double diffuser should to be changed to handle the increased amount of CFM.
    O.K.

    The Main Trunk Take-off equivalent lengths, are important to effect efficient airflow.

    Make certain there are ample Return Air paths for those rooms![/QUOTE]

    thanks.

    AM

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