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  1. #1
    Join Date
    Aug 2001
    Location
    NJ
    Posts
    38

    Hmm

    I have a customer that calls me every season to service the unit (5 ton common central unit)
    The unit is doing a good job but the metal duct is 11" wide by 4" deep and to me I think thats to small.
    She has no air upstairs to speak of and Shes blocking off all the vents to try to force more air up stares.
    I checked all the duct work and everything is all metal and just about no leaks to be concerned about but I did tape the seams anyway.
    The biggest problem is She doesn't want a fan installed because the noise travels into the room and keeps her awake.'
    Last year She paid me to install a fan in the duct and I also installed a sail switch but to much noise for her.
    So now i'm thinking of installing a fan over the vent and have it PULL air rather then have a fan in the duct force air.
    Also the vent closest to the unit does not impressed me with the flow so at this time I like to increase the efficiency and then see what happens.
    Home is a large split level with 3 rooms above and the main bed room above the garage.
    Right now i'm lost on this one.
    Any suggestions?
    Vegas/

  2. #2
    Join Date
    Sep 2004
    Posts
    3,157
    Have a professional come out and do a manual "J" and a manual " D" and install new duct work that has been properly sized for the unit / home

  3. #3
    Join Date
    Mar 2005
    Location
    NC
    Posts
    224
    Your ductwork is way under sized. I'd pull a load calculation on the whole house to check and see if the unit is sized correctly. Your ductwork should start around a 20x15.

  4. #4
    Join Date
    Apr 2004
    Posts
    201
    You're not going to help anything by adding a fan. The lack of airflow is due to turbulence and restriction in your(or her)under-sized ducts and trying to push more air (or pull it) through there is just going to make things worse by increasing static pressure and turbulence and noise. Most times these kind of things can be fixed without replacing all the ductwork though. It's the fittings at the unit that make the biggest impact on flow through the system. I say "most times" cause 11X4" trunk is awfully under-sized and you may just have to rip it all out to fix this one. You really need a duct man to look at it to know. Someone with manual D and J training like was already suggested.
    ...SHEEESH!!!

  5. #5

    Frown

    my idea is:
    if you have space,you need not rid out of the 11x4 duct,you can plus an other duct parallel the 11x4 duct.
    the first thing is that you'd better knowing the correct size duct you need .

  6. #6
    Join Date
    Nov 2000
    Location
    Waco, Texas, USA
    Posts
    6,153
    Are you sure it is lack of air flow and not a controls problem? Which level is the thermostat located?
    "And remember my sentimental friend......that a heart is not judged by how much you love, but by how much you are loved by others" - Wizard of Oz.

  7. #7
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983
    You need TEN INCHES of water column to cram 2000 cfm into that duct. (that is IF it don't have any liner)

    You dont' need a duct fan....You need this





    There's no way the unit could have really done anything with that small of duct. Were you actually saying the duct feeds 3 bedrooms and a master bedroom over a garage?
    If so, its still not big enough. 11x4 duct will only be big enough to feed one room by itself.... but thats ONLY if the duct feeding it is OK.


    Extend to others the grace that God has given you.

  8. #8
    Join Date
    Jan 2005
    Location
    daytona florida
    Posts
    76
    You're not going to help anything by adding a fan. The lack of airflow is due to turbulence and restriction in your(or her)under-sized ducts and trying to push more air (or pull it) through there is just going to make things worse by increasing static pressure and turbulence and noise. Most times these kind of things can be fixed without replacing all the ductwork though. It's the fittings at the unit that make the biggest impact on flow through the system. I say "most times" cause 11X4" trunk is awfully under-sized and you may just have to rip it all out to fix this one. You really need a duct man to look at it to know. Someone with manual D and J training like was already suggested.
    __________________
    ...SHEEESH!!!bodhisatva




    04-03-2005 12:02 PM
    oh my god what is the deal with people these days this one is correct you are not going to accomplish anything with a fan waste of time

  9. #9
    Join Date
    Mar 2005
    Posts
    12
    Some how you have to get the ducts sized correctly. Who ever you hire to do this must perform a room-by-room load calculation. It is the only way to determine proper duct size. Tell her to not to through any more money out the window on fans and substitute quick fix experiments.

  10. #10
    Join Date
    Sep 2004
    Posts
    3,157
    I have a customer that calls me every season to service the unit (5 ton common central unit)
    The unit is doing a good job but the metal duct is 11" wide by 4" deep and to me I think thats to small.
    She has no air upstairs to speak of and Shes blocking off all the vents to try to force more air up stares.

    translation:

    he bought a 5 ton unit and he is trying to fit it in the place of his old 2 1/2 ton

    he has no air upstairs to speak of and hes blocking off all the vents to try to force more air up stares.
    (stairs)
    and although he is a licenced HVAC contractor "working on a customers system, he has never heard of manual J-D- rule of thum -ductulator or any other method of sizing ductwork

  11. #11
    Join Date
    Aug 2001
    Location
    NJ
    Posts
    38

    Lack of air up stares

    Thanks to all who responded.
    Last season when I went under the craw space I saw the problem.
    Also the 5 ton unit did not replace a smaller unit.
    This is an original install when the home was built 25 years ago but She knows more the me:-)
    She feels that if it was built with the home then the duct work is correct.
    I tried to explain to her that the air moves faster in the center on the duct but i'm wasting my time with her.
    I do some HVAC in a loca hospital and I had the plant engineer speck to her with no results.
    Now She wants me to relocate the unit to the other side of the house to keep it out of sight:-)
    I suggester a small window unit and She said no.
    I suggested a fat to blow the cooler air below up the stares and She says no
    I have a tin knocker going there today and look things over and give her an estimate.
    Thank sto all who responded.
    I appreciate all the input
    Vegas/

  12. #12
    Join Date
    Sep 2004
    Posts
    3,157
    so am I to understand that the solution to this is going to be to simply add ducts to the upstairs rooms?

    What size ducts is your "tinknocker" going to add to increase air flow to these rooms.

    What were the results of your manual J and manual D calculations?

    This system has been in place and working fine for 25 years? and now you are having airflow problems?

  13. #13
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983
    Vegas,

    I believe knowledge of proper load calculations and air distribution is the most valuable tool you will have
    as a technician.

    It sounds like the approach you are taking to the problem is....
    A. Lets try this.
    B. That didn't work. Lets try this.
    C. That didn't work either. Lets try this.
    It sounds like a guessing game and no real diagnostics involved.

    The best approach to a prob with a room or section of house that is not comfortable is.
    A. Check duct system for air leaks or crushed pipe (plumbers, termite men, etc sometimes crush pipe to get into tight spots).
    Is the prob a 'new' prob or an 'old' prob?

    B. Load calculation on the house
    A good place to start (as mentioned by others)
    is ACCA Manual J. You will be able to determine how much air you really need.

    C. Check for proper / sufficient air distribution system.
    ACCA Manual D is a good place to start with that.
    There is a member of our sight..... NormChris that is
    a trainer for Bacharach, he has some books he suggests also that will give you a good knowledge of air distribution among other things. Here's a link...
    http://www.bacharach-training.com/norm/recommended.htm

    After performing B and C... you should have a real good direction on where to go to next without it being a guessing game.

    I understand it sounds like your customer is also wanting to do things her way and diagnose the stuff herself from the sounds of things. I know thats a tricky situation and
    one that will be hard to get to come out on a good foot.
    It sounds like you may have actually lost credibility with the customer due to not having a good evaluation and diagnostic procedure.
    One other resource I can give you to help with customer relations and becoming a profitable technician...
    http://www.hvacprofitboosters.com/DVD/Page_1.htm
    Its a little cheezy but there is alot of great info in there.

    Here's another peice of advice....
    You might want to put something in your sig line
    saying you are a tech in training or something to that
    extent. Other guys on this board are going to assume you
    are a tech that should know what you are talking about, and if they smell something fishy.... they'll eat you for breakfast.




    [Edited by wormy on 04-04-2005 at 08:18 PM]
    Extend to others the grace that God has given you.

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