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Thread: Ducting

  1. #1
    Join Date
    Aug 2008
    Location
    Houston,TX
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    18

    Ducting

    The more I read this forum the more I appreciate this line of work and enjoying learning about it.

    I have a question about the different types of ducting. In particular, I was informed that my 16 SEER unit would not actually reach that level b/c of the type of ducting I have (builders grade, I think he said R5?).

    Would someone be able to provide the different types of ducting material and how it relates to achieving the stated SEER rating of a particular system? If there are specific details which seperate the different types what are they? My assumption is that they provide better insulation and possibly even provide a different material which makes up the inner shape?

  2. #2
    Join Date
    Dec 2007
    Location
    Cedar Grove, Wi-Sheboygan
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    1,582
    The type of material used for your ducting doesn't determine how well your HP or AC unit performs, having the proper size ducting is one of the reason your HP/AC unit will or will not perform as rated along with the proper size indoor coil and proper charge of the system is directly related to how well your system perfroms. The type of air handler, forced air furnace also detemines how well the HP/Ac will perform as well, it will also depend on if you have a varible or single speed blower in your air handler/forced air furnace too. When you have all the proper componets e.g right size ducting, proper size HP/AC, the proper indoor coil and charge and the right type of furnace/air handler blower (single speed, 2 stage, or varible) will if done correctly will give you in your case a 16 seer rating and in some cases maybe a point higher and possibly a point lower in seer. So having the hard duct or flex duct doesn't determine over all performance of a 16 seer AC/HP.

  3. #3
    Join Date
    Jan 2004
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    Lancaster PA
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    He may have been refering to the fact that if your duct is in an unconditioned attic. With only R5 insulation value, you will lose some of the efficiency your paying for.

    I would get a second opinion though.

    Some companies don't like 2 stage equipment, and will come up with excuses not to install it.
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  4. #4
    Join Date
    Feb 2008
    Location
    Waffleville
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    depending on local codes, R-8 is about the highes insulation value for duct systems

    also making sure the system is sealed well and not allowing your conditioned air to leak out or allowing non-conditioned air to leak into the duct system will make a larger difference in performance than the difference between R-5 and R-8 how old is your duct system? if it is over ten years old i deffinately consider replacement, and make sure that i found a contractor that reall knows what he is talking about most Co's give free estimates
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  5. #5
    Join Date
    Aug 2008
    Location
    Houston,TX
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    My ducting was installed in 2001. I had someone come by who thought I shouldn't go with a 16 SEER two stage and instead go with a single stage 14. I was told the two stage systems have a lot more things to go wrong which are more costly to repair.

    BT, you were correct, I was wondering what is the difference in the R-5 and R-8? How much better (quantified possibly in degrees lost over time?) do these differences make? Maybe I'm taking this a bit far but I am gathering it's not just diameter but thermal capability being the difference?

    Also Dan, I have a Honeywell IAQ 9421 and a two stage 16 SEER, now considering the 14SEER single, both with a v/s furnace.

  6. #6
    Join Date
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    R5 duct transfers about .08 more BTUs per sq ft per °F difference then R8.

    Or, if your attic is 125°, and the air in the duct is 50°, then about 6 BTUs more per sq ft then R8 insulated duct.
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