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Thread: Lineset Sizing

  1. #1
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    Lineset Sizing

    I have a customer looking to replace his 3.5 ton 22 year old Lennox A/C and coil with a 13 SEER system. He currently has a 3/4 X 5/16 line set @ 30' long. I told him we needed to install a 7/8 X 3/8. All other contractors told him he was OK with what he has. Where can I get some information to back me up, or am I wrong here?

    Thanks!
    In the land of the blind the one eyed man is King! semper fi

  2. #2
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    Assuming four long radius 90 bends in the 30' line set, AS/Trane's refrigerant line sizing software recommends 3/4 x 3/8, but 3/4 x 5/16 and 7/8 x 3/8 are both ok too.
    The difference between a 3/4 x 5/16 line set and a 7/8 x 3/8 is a about 430 btuh of capacity, roughly 1%.
    It isn't worth the cost of replacing the lines to get that 1%.

    The smaller lines will potentially result in a more reliable system, due to lower total refrigerant volume, and better oil return.
    If more government is the answer, then it's a really stupid question.

  3. #3
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    Mark,

    Which Trane software do you use? The engineering toolbox?

  4. #4
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    Quote Originally Posted by Brent Ridley View Post
    Mark,

    Which Trane software do you use? The engineering toolbox?
    The Adtec software.
    It is the software you get if you order the piping software Publication 32-3312-0 listed in the outdoor unit service facts on AS/Trane residential equipment.
    I don't know what the cost of it is now, but a few years ago it was around $160.
    If more government is the answer, then it's a really stupid question.

  5. #5
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    Quote Originally Posted by hvac4u View Post
    I have a customer looking to replace his 3.5 ton 22 year old Lennox A/C and coil with a 13 SEER system. He currently has a 3/4 X 5/16 line set @ 30' long. I told him we needed to install a 7/8 X 3/8. All other contractors told him he was OK with what he has. Where can I get some information to back me up, or am I wrong here?

    Thanks!
    Mark is 100% correct. How hard would it be to just replace the 5/16 line only? I have found on many jobs the bigger line isn't worth the trouble but sometimes the liquid line can be changed without to much trouble.

    Mark what does your software say if this were a 15 seer system out of curiosity?

  6. #6
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    Quote Originally Posted by Barrettservices View Post
    Mark what does your software say if this were a 15 seer system out of curiosity?
    SEER is not a variable taken into account in refrigerant pipe sizing.
    If more government is the answer, then it's a really stupid question.

  7. #7
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    With running 5/16th on the liquid line instead of 3/8th there will be a higher head pressure. By under sizing the liquid line you would think the extended head pressure would hurt a compressor some.

  8. #8
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    Quote Originally Posted by mark beiser View Post
    Assuming four long radius 90 bends in the 30' line set, AS/Trane's refrigerant line sizing software recommends 3/4 x 3/8, but 3/4 x 5/16 and 7/8 x 3/8 are both ok too.
    The difference between a 3/4 x 5/16 line set and a 7/8 x 3/8 is a about 430 btuh of capacity, roughly 1%.
    It isn't worth the cost of replacing the lines to get that 1%.

    The smaller lines will potentially result in a more reliable system, due to lower total refrigerant volume, and better oil return.
    Need to know if the indoor is higher then the condenser, and if so by how much.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  9. #9
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    Good info!

    Quote Originally Posted by Baycienda View Post
    With running 5/16th on the liquid line instead of 3/8th there will be a higher head pressure. By under sizing the liquid line you would think the extended head pressure would hurt a compressor some.
    this is a ranch on a slab, lineset @ 30', coil 12' above compressor


    Thank you for your input. I have leaned something here
    In the land of the blind the one eyed man is King! semper fi

  10. #10
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    I'm surprised the R410a system requires larger lines than a R22 system.

  11. #11
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    Quote Originally Posted by 54regcab View Post
    I'm surprised the R410a system requires larger lines than a R22 system.
    It doesn't.
    If more government is the answer, then it's a really stupid question.

  12. #12
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    Quote Originally Posted by mark beiser View Post
    It doesn't.
    Is it the 13 SEER that's requiring the larger lineset?

  13. #13
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    Quote Originally Posted by 54regcab View Post
    Is it the 13 SEER that's requiring the larger lineset?
    I just had a rheem 3-ton 13 seer 410a install today that spec. 7/8" @ the condenser but the same 3ton 15 seer only spec 3/4" @ condenser. why is this?

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