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  1. #1
    Join Date
    Mar 2017
    Houston, Tx
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    Question Balancing a Pre Existing System

    Just got through with ACCA Manual D online course and I'm wondering what the work flow looks like when you walk into a customers house to do duct balancing?

    When you are the one that is installing a system, you've done a Manual J and room by room load calculations, the Manual D duct design, chosen the proper equipment/ducts to supply the necessary air flow. You know that information because you did all the work.

    But what do you do when you walk into a situation where you haven't done any of that and are concerned the air flow might not be balanced well in the house?

    Do you start from scratch with a load calculation and duct design?

    What if the installed equipment/ducts aren't right and you are trying to help the customer by working with what is currently there?
    (Thinking in terms of a customer that bought a system within a few years and not ready to shell out a bunch of money for a new system.)

  2. #2
    Join Date
    Feb 2016
    Louisburg Kansas
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    Unless the branch ducts have dampers or unless you have manual zone dampers balancing residential is a stop gap solution. Face dampers are often adjusted by the residents by accident or on purpose and accidentally. If you want to work with what is there you have two things to work with plus intuition. Make sure the filters are clean and the fan is producing the maximum amount of air possible. Measure the total airflow and the square feet of floor space in each conditioned space. Proportion the air according to the area of each space evenly. The intuition part is that from there you add a little air or subtract a little according to expected heat load due to sun exposure etc. On multi story houses you need main duct dampers for the floors with winter/summer set points.
    That may sound like hit or miss but it is quick and affordable. After you do a few it works well.

  3. #3
    Join Date
    Sep 2008
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    Is this not an exercise in futility???

    I typically suggest the homeowner add or increase a return because 99% of residential systems are underfed. Not to mention filters are not serviced as frequently as they should be.

    Restricting air should only be done if there is enough of air to begin with. That would be an easy check by checking available static pressure. If you're already over mfg. suggested .5"wc then just be careful not to go too much higher. Once you exceed .75 your volume is likely going to suffer with a PSC, or your efficiency with an ECM. If there is not enough available, which is typically the case, I would suggest adding supply air volume to the rooms that are not comfortable.

    Where there is enough volume, I like trying cheese cloth or supply diffuser filters first. This reduces air flow without adding the noise typically accompanied by using the grille damper to restrict the flow. The homeowner must be instructed the filters do need to be cleaned or replaced, just like the return air filters.
    "The only true wisdom is in knowing you know nothing" Socrates

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