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Thread: Manual J ?

  1. #1
    Join Date
    Jan 2008
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    78

    Manual J ?

    folks--tech is finally making back to my house today..

    quick ?..when doing a man J calc, should you take into account halways & closets & baths? we have center hall colonial with very wide hallways..wondering how that impacts man J

    Also, would the calc change much if rather than measuring each room, I measure the overall dimensions (as long as all the windows were properly figured in)?

  2. #2
    Join Date
    Jan 2004
    Location
    PA
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    The hallway has a ceiling and floor doesn't it. Its part of the houses load.

    A wole house load calc is ok to size the equipment.
    Won't tell you CFM to teh rooms though.
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  3. #3
    Join Date
    Jun 2001
    Location
    DFW
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    684
    The room by room measurements are to determine the load for each room - which will help determine how much air flow each room needs.

    The whole house measurments give you a quicker way to determine the output you need from your HVAC equipment.

  4. #4
    Join Date
    Jan 2008
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    78
    thanks so much for you help over the past few weeks guys...

    my wife told me yesterday that we did get some form from the installer for our rebate....low and behold a manual J calc...according the calc, the total sq ft of our house is 1600....I just did an overall measurement...2100+...think that might be impacting my system...lol

    one last ?....at least for today.

    with a zoned system (upper and lower) with one a/h, shouldn't the speed of the a/h change based on whether 1 or both are calling for air--otherwise if only 1 zone is calling for air, you get 2x the flow. or in my case, probably 2.5-3 since the upper sq footage is not the same as the lower..

  5. #5
    Join Date
    Jan 2004
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    PA
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    Depends on your duct system.
    First stage could still be more air then one zone needs.
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  6. #6
    Join Date
    Jan 2008
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    right now, the first stage isn't working, so it goes right to second stage...when both zones are calling for air, we can sleep at night..if only the upper is calling, jet engine..

    when they cranked up the airspeed, it helped with the downstairs temp, but caused the problem at night...

  7. #7
    Join Date
    Jan 2004
    Location
    PA
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    Until they get it wired right, your hosed.
    And, you not doing your VS blower any favors either.
    Running a VS at real high static pressures, decreases their life span.
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  8. #8
    Join Date
    Jan 2008
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    Beenthere....when are you opening an office in Northern NJ?

  9. #9
    Join Date
    Jan 2004
    Location
    PA
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    LOL..

    There are some good guys from this site in NJ.

    If I was going to relocate, I think it would be Alaska, I like cold weather.
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  10. #10
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
    Posts
    1,051
    What brand of zone system do you have? Is there a by-pass installed to deal with the extra air? As stated you need to get the stages working.
    Its a good Life!

  11. #11
    Join Date
    Jan 2008
    Posts
    78
    there is a by-pass (or so I'm told)...the A/h & unit are Trane, xl16i....the quote doesn't specify the zone panel, but I can check when I get home tnt.

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