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  1. #14
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    Jan 2004
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    Quote Originally Posted by Thebil Illpay View Post
    Here's one of them. After I get back from the store I'll post some others. I really hope one of you answers them.

    I have sheetmetal @8" round ductwork in the attic supplying the upstairs bedrooms. Right now, I definitely have major airflow issues so I'm going to do something about it. Would I be better off having the existing ductwork cleaned and sealed, and reinsulated as necessary ,or, buying new ductwork which will most likely be flex duct because that is what it seems many guys want to install.
    Be better off having a company find out what the problem is.
    Don't just through money at guess work.
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  2. #15
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    Quote Originally Posted by Thebil Illpay View Post
    Trane split from American Standard in about 2006. Prior to that, was the engineering and quality control similar?
    ?????
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  3. #16
    Join Date
    Oct 2005
    Location
    MN
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    133
    My Ruud mod is probably oversized one size, but it's zoned. It's set up to only run at 40% on the two smaller zones and the third (large) zone modulates. The smaller zones are a perfect match for the heat loss at the 40% fire at 15-20 degree OAT. Extremely comfortable! Temp never varies by 1/2 degree.

  4. #17
    Join Date
    Apr 2008
    Location
    Alberta Canada
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    2,246

    Not trying to Hi jack

    [QUOTE=beenthere;2765722] York use to rate by output, instead of input like most everyone else.


    How do they do that. what about high alt? output in you city is different than mine. We get less.
    Do it right the first time.

  5. #18
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    They just did.

    Derate works the same weather its rated by input or output though.

    They rate them by input now though.
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  6. #19
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    Apr 2008
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    Alberta Canada
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    Not saying that just makes less sense

    Quote Originally Posted by beenthere View Post
    They just did.

    Derate works the same weather its rated by input or output though.

    They rate them by input now though.



    I size by output and know I have to derate in high Alt, just makes more math.
    Do it right the first time.

  7. #20
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    Jan 2004
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    PA
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    I'm at rough 460 foot above sea level. I don't have to do that derate stuff.
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  8. #21
    Join Date
    Feb 2007
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    999
    Quote Originally Posted by beenthere View Post



    ........EG: 70,000 90% 65 rise, 897CFM, 90,000 65 rise, 1153CFM.
    Been, I've noticed that you frequently quote CFMs for various temperature rises, etc. Is there a convenient formula for doing that or are you reading off of a chart?

    Amp

  9. #22
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    Jan 2004
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    Quote Originally Posted by ampulman View Post
    Been, I've noticed that you frequently quote CFMs for various temperature rises, etc. Is there a convenient formula for doing that or are you reading off of a chart?

    Amp
    There is a formula.

    But I use a spread sheet.
    Its easier, then me doing the math. And less chance of me screwing the math up.
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  10. #23
    Join Date
    Nov 2004
    Location
    SW FL
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    6,428

    Thumbs up Simply ... at / close to sea level

    Quote Originally Posted by ampulman View Post
    Been, I've noticed that you frequently quote CFMs for various temperature rises, etc. Is there a convenient formula for doing that or are you reading off of a chart?

    Amp
    Heat Output / [ CFM * 1.08 ] = 'F

    I.E.
    90,000 * .9 = 81,000
    81,000/ ( 1,153 *1.08) = 65'

    1153 * 1.08 = 1245.24 =
    65.047
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  11. #24
    Join Date
    Nov 2004
    Location
    SW FL
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    Question REAL Needs ?

    Quote Originally Posted by noobs View Post
    OK, that seems to make sense. There is general reluctance in the industry (at least in my area) to do Manual J calculations. My current set up is as follows:

    York
    Condenser: H1RA048S06D
    Coil: G1UA048S17B
    Furnace: P4UB16N06401A

    In the summer, the AC runs almost constantly during the hottest and will not keep up in the afternoon if there are many people in the house. Temperature creeps up.

    In the winter, on cold, windy days, the furnace runs non stop and it “feels” a little chilly. Recovery time from a set back is almost not possible. Maintenance of temperature only. I have to turn the gas fireplace on as a supplement.

    One contractor commented that it was odd to have a 64,000 BTU furnace matched with a 1600 cfm blower and 4 ton coil and AC. I was also told that with older furnaces, the 64,000 was output spec and that input is 80,000 BTU at 80% AFUE.

    So as a starting point, is this far off?

    4 ton 2 stage AC with matching coil
    100,000 BTU (input) modulating furnace

    Since the modulating furnace draws combustion air directly from outside, I was also planning to close the 6” fresh air intake that goes into the cold air return.

    I’m still working on finding someone to do the manual J and will try to buy the HVAC calc program to do it myself as a check.

    Would those specs be that out of whack?
    100,000 @ 90% might handle ~ 3,000+ Sq. Ft residence in a cold climate

    Need REAListIc sizing ... see my profile.

    Windows and infiltration/tightness need to be well defined for
    results to match actual operation.

    Guess that open 6" outside air duct may provide as much as 140 CFM.
    140 CFM * ( 120'F - 20'F) * 1.08 =
    15,120 BTUh Minimum
    120 Delivered
    - 20 Outside
    100 Difference
    * 140
    14,000
    *1.08
    15,120

    In other words, the 6" duct should at least have a damper to restrict air to 1/3 to 1/2 ... 50 to 70 CFM
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  12. #25
    Join Date
    Jan 2009
    Posts
    386
    Quote Originally Posted by dan sw fl View Post
    Heat Output / [ CFM * 1.08 ] = 'F

    I.E.
    90,000 * .9 = 81,000
    81,000/ ( 1,153 *1.08) = 65'

    1153 * 1.08 = 1245.24 =
    65.047
    I've seen this formula quoted several times on this forum, and I'm guessing it's what beenthere has in his spreadsheet. The thing to note about it is the multiplier 1.08 is highly dependent on altitude. The following table shows what should be used instead of 1.08 (unless you're at, or near, sea level - 0 ft. altitude):



    (the source of that image can be found here)

    So, if you live in Denver, CO (alt. of 5298 feet), the numbers would work out to be:

    90,000 BTU/H * 0.9 = 81,000 BTU/H
    81,000 / (1408 CFM * 0.885) = 65 degree rise

    So, the difference in altitude means a difference in CFM needed to move the BTUs (1408 CFM needed, instead of 1153). Altitude should definitely be taken into consideration when using that formula.

  13. #26
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    PA
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    That is the formula in the spread sheet.

    I'm at rough 460 foot above sea level, so I'm safe with out correcting for density.
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