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  1. #1
    Join Date
    Mar 2009
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    Montana
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    10

    Excessive blow-by air in Zone 1 when only Zone 2 called.

    I had a 2 Stage-2 Zone Trane heat pump/furnace system installed about 6 months ago. Except for the main trunk to Zone 1, the duct runs from the basement to the existing upper floor duct work were reconfigured and dampers added to give us 2 zones, one for each of 2 upper floors, about 1000sf each. Overall the system works pretty well, except for the continuing problem of excessive blow-by through the main Zone 1 vent when only Zone 2 is called. There is only negligible passive air seeping through the other Zone 1 vents at the same time. To try to minimize the blow-by, the HVAC contractor installed a by-pass from the main Zone 1 trunk and replaced 6" runs with 8" runs to the Zone 2 ducts to reduce air-flow resistance. Those measures helped a bit. Now Zone 1 heats to two degrees less than the temp set for Zone 2 when only Zone 2 is called. It used to be 2-3 degrees hotter in Zone 1 when only Zone 2 was called. The tech was here last week and we measured the blow-by air blowing out the main Zone 1 vent when only Zone 2 is called. It registered as 8 cfms(?) at both heat pump stages and 15 and 20 respectively at furnace Stages 1 and 2. This is after the above measures were taken. Consequently, we are not getting the cost benefits of having 2 zones.

    Questions:

    1) Is there an industry standard for the maximum blow-by that should come out of the "off" zone vents when only the other zone is called?

    2) It has been suggested that a second damper in the large main trunk would catch the air blowing through the first damper when it is closed. Would that help?

    3) Would it help if they reduced the size of that main trunk?

    4) Any other suggestions?

    All advice is appreciated. Thanks a million!

  2. #2
    Join Date
    Jan 2004
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    Lancaster PA
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    Probably used the wrong size zone damper.
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  3. #3
    Join Date
    Mar 2009
    Location
    Montana
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    They already replaced a smaller damper with the largest one that fits the non-standard duct. I was told it still left about 1" open around it, which they foamed to fill it in. I still need to know how much blow-by in acceptable, so I know when they have reasonably solved the problem.

    Thanks

  4. #4
    Join Date
    Jan 2004
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    Less the 10%.

    They should have special ordered the correct size for that duct work.
    Not just used standard stocked sizes.
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  5. #5
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    Mar 2009
    Location
    Montana
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    Beenthere, thank you. What should I insist they do to solve the problem? Special order new one? Is adding a second damper a reasonable thing for them to do?

  6. #6
    Join Date
    Jan 2004
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    Lancaster PA
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    No, a second damper is a band aid, to cover up an improper install.

    They can order a damper to fit your duct.

    if its a truely odd ball size( 91/8", as an example ), yea, they won't be able to get that.

    I don't think I've ever had more then 5% leakage.
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  7. #7
    Join Date
    Mar 2009
    Location
    Montana
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    The external measurements of the trunk/duct is 24"W x 7.25"H. Are there different types of dampers, some that close more tightly than others?

  8. #8
    Join Date
    Oct 2003
    Location
    Washington
    Posts
    7,405
    You know it's touchy with zone dampers.

    A lot of variables, from how much care the guys took installing them, to what brand they installed.

    I tend to favor the Honeywell Zone dampers as they tend to have a low leak rate.

  9. #9
    Join Date
    Jan 2004
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    Quote Originally Posted by wildflower View Post
    The external measurements of the trunk/duct is 24"W x 7.25"H. Are there different types of dampers, some that close more tightly than others?
    In cases like that, I get the damper in the 8" height, and make a transition for it.

    Sounds like a Salesman Oooops. he didn't measure the duct when he sold you the zone system.
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  10. #10
    Join Date
    Mar 2009
    Location
    Montana
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    It's a Honeywell damper. The Damper actuator reads 24VAC 60Hz 6W. Is that the size 24"L, 6"W? What should they have installed?

    GO BOLTZ - Lived in SD 11 years, moving back in couple years.

  11. #11
    Join Date
    Mar 2009
    Location
    Montana
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    Hmm

    Quote Originally Posted by beenthere View Post
    In cases like that, I get the damper in the 8" height, and make a transition for it.

    Sounds like a Salesman Oooops. he didn't measure the duct when he sold you the zone system.
    What is a transition? And, what do you mean salesman ooops? Can we not do zones effectively because of the duct size? The salesman was the owner of the company.

    Forgive my naivete, but I am so out of my element and trying to self-educate so I can have an intelligent, informed discussion and get what I paid for.

    Thanks for you patience.

  12. #12
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    I mean the salesman should have measured up the duct to order the correct size dampers, when he was there.
    Then he would have seen that the duct was not a standard size.
    And could have included the cost of a transition piece for the damper.

    In your case, it would have been, transition pieces, and a sleeve for the damper.
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  13. #13
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    Quote Originally Posted by wildflower View Post
    It's a Honeywell damper. The Damper actuator reads 24VAC 60Hz 6W. Is that the size 24"L, 6"W? What should they have installed?

    .
    No, that the motor ratings.
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