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  1. #1
    Join Date
    Mar 2011
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    Seattle
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    7

    Control zones via return air?

    Sorry if this has been covered before, but I did do a search on the forum and found nothing related. I think I know the answer to this, but I can't rule it out until I get a sanity check. My home could really benefit from zoning to manage different levels of the house. The trouble is that the supply duct work is too intertwined between the floors to separate. Redesign & replace of supply duct work means ripping out ceiling and wall sheet rock – not going to happen. The return air, however, is cleanly separated between floors and would require just two control dampers. I've never heard of this being done, so can I assume that it is unwise to pursue that approach? Ineffective? Cost prohibitive? Unlikely to find contractor experienced in such an approach? If it matters, one floor uses a round duct (about 12”) and the other is rectangle (estimate 10x16).

  2. #2
    Join Date
    Feb 2007
    Posts
    999
    WAG: NO. I'll let the PROs elaborate.

    Amp

  3. #3
    Join Date
    Apr 2004
    Location
    MN
    Posts
    1,838
    Not recommended at all. Air is harder to pull than it is to push. You will end up starving the system of air, causing premature blower motor, heat exchanger and compressor failure. Plus, you will still be blowing conditioned air into all the rooms you don't necessarily need it in. Plus, if your doors are slightly undercut, this makes a perfect return air path to the nearest return air grille, which will negate any attempts you have made at zoning the return anyhow. Hope this helps.

    You could try running your fan continuously so the air in the house does not have a chance to stratify.
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  4. #4
    Join Date
    Jan 2004
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    PA
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    There are zone systems out that use dampers/bladders installed at each register to control zoning. No messing with separating the supply ducts then.

    Forget about trying to control it with the return ducts.
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  5. #5
    Join Date
    May 2011
    Location
    NV, NOT Las Vegas
    Posts
    66
    beenthere, thats funny you bring that up, I actually saw a guy do this on one of the hgtv or diy shows. he had a method of blowing string through the supply ducts with a 'parachute' and pulling back a series of tubes to the main blower/furnace, each connected to a bladder and hooked up to an air source of some type. Each room had a t-stat that controlled the air source to open or shut the supply register off. Pretty cool idea, no demolition of walls and not a ton of labor costs.

  6. #6
    Join Date
    Mar 2008
    Location
    Long Beach, CA
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    3,730
    Quote Originally Posted by beenthere View Post
    There are zone systems out that use dampers/bladders installed at each register to control zoning. No messing with separating the supply ducts then.
    Isn’t zoning or blocking half the supply registers as harmful to the heat exchanger and coils as blocking half the return air?

  7. #7
    Join Date
    Jan 2004
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    PA
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    Quote Originally Posted by Brian GC View Post
    Isn’t zoning or blocking half the supply registers as harmful to the heat exchanger and coils as blocking half the return air?
    Its a communicating system. It open other zones to maintain set temp even if that zone isn't calling, to prevent short cycling. So most of the time, other zones will still be partially open. Along with it using a modulating bypass to maintain air flow through the unit.
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  8. #8
    Join Date
    Dec 2010
    Location
    The Quad-Cities area (midwest).
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    2,744
    First, don't try to zone the return air.

    Can you get to most of the supply ductwork? Zoning the supply may be able to be accomplished.

    As B.T. said, there are differant methods available.

  9. #9
    Join Date
    Mar 2011
    Location
    Seattle
    Posts
    7
    Thanks all for taking the time to answer my question. I will heed the wisdom and not consider using return air for control. As far as controlling the supply air, the sprawling duct work would force me to use individual vent dampers – all 22 of them!

  10. #10
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
    Posts
    1,787
    I've even seen home made zoning registers (using cheap model style servo motors). As for cutting down too much air, if there is that many dampers cut back, it should be cycling the system off at that point.

  11. #11
    Join Date
    Aug 2009
    Location
    Jurupa Valley, CA
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    Something I see often is people actually IGNORING return when installing a zoned system. Zoning off half the house's supply ducts is great, but if you leave the return ducts wide open, you defeat half the purpose.

  12. #12
    Join Date
    Dec 2010
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    The Quad-Cities area (midwest).
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    Quote Originally Posted by Bitrate View Post
    Thanks all for taking the time to answer my question. I will heed the wisdom and not consider using return air for control. As far as controlling the supply air, the sprawling duct work would force me to use individual vent dampers – all 22 of them!
    If you can get to the ductwork it can be done (easily) with individual dampers.

    You may be surprised, it may not take 22 dampers. I normally will suggest manually dampering basement supplies if there are not that many.

  13. #13
    Join Date
    Mar 2008
    Location
    Long Beach, CA
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    3,730
    Quote Originally Posted by CraziFuzzy View Post
    Something I see often is people actually IGNORING return when installing a zoned system. Zoning off half the house's supply ducts is great, but if you leave the return ducts wide open, you defeat half the purpose.
    Most vocal pros on this forum feel that the return air location has absolutely no effect on the performance of an AC or heating system as long it is unrestricted. I feel they are incorrect and it is a major oversight on their part but will not argue the point anymore.

    If you are aware of the fact that the return air removes the sum total of all supply air and that it should be located where it removes “bad air” first, you are on the right track to fine tuning your system. But do not expect many pros here to understand what you are talking about.

    So, if you are hinting at having switchable or zoned return air ducting along with a zoned system you are ahead of the curve, IMO.

    PS - I mistook you for the OP, but my comments still stand.
    Last edited by Brian GC; 05-13-2011 at 05:55 PM. Reason: clarification

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