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Thread: Seeking alternative to wall breakout and line set replacement

  1. #1
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    Seeking alternative to wall breakout and line set replacement

    Residential installation.
    Retiring my R22 system and upgrading to R410A. Increasing from 2-ton 13 SEER to 3-ton 14 Seer. Compressor on roof, Evap. is subfloor. 25' line length. Existing suction is 3/4" tube, new suction spec. is 7/8".
    Question: Will this work? I want to leave the existing (13' length) 3/4" tube vapor line in the wall, and adapt to 1-1/8" tube in the subfloor, length as needed, to give me an equivalent volumetric area calculated to match a 25' length of 7/8" tube. My reasoning is that the increased friction of the existing undersized 3/4" tube will be offset by the reduced friction of the oversized 1-1/8" tube.
    Robert S.

  2. #2
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    The refrigerant line set should be fine. The bigger problem is how a 3 ton unit will work on 2 ton duct system.

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  4. #3
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    How are you going to increase the ducts 50% too match the new equipment?

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  6. #4
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    Quote Originally Posted by rske View Post
    Residential installation.
    Retiring my R22 system and upgrading to R410A. Increasing from 2-ton 13 SEER to 3-ton 14 Seer. Compressor on roof, Evap. is subfloor. 25' line length. Existing suction is 3/4" tube, new suction spec. is 7/8".
    Question: Will this work? I want to leave the existing (13' length) 3/4" tube vapor line in the wall, and adapt to 1-1/8" tube in the subfloor, length as needed, to give me an equivalent volumetric area calculated to match a 25' length of 7/8" tube. My reasoning is that the increased friction of the existing undersized 3/4" tube will be offset by the reduced friction of the oversized 1-1/8" tube.
    Robert S.
    Answer: No it will not work.

    Sent from my SM-G965W using Tapatalk

  7. #5
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    Thread Starter
    Thanks for the quick response. 3 response so far, 1 says: No won't work. 1 says: Should be fine. 1 says: Duct size? The air duct system is oversized, good for more than 3-tons. I guess I'm looking for a response with some science behind it as to why it will work or won't work.
    Robert S

  8. #6
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    What brand? I have not seen a 3T that takes 7/8" until you get excessively long. 25' is not long.

    If 2T has done fine why the increase in size?

    And my guess is the duct work is not good for 3T. Most duct systems are not good for the size that is on them.

    Did they do a load calc or did he just say you need a 3T. This whole scenario sounds like a big upsell where you spend more than you need to and end up with worse comfort that they can't figure out.

    Did I read that right the unit is going on the roof and the coil is in the crawlspace /basement? Why not set it on the ground where it will carry less noise in the house and they can easily run new lines of the necessary size without the lift associated with your current set up.

    At this point I would say keep looking.

  9. #7
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    Your scheme about oversizing one section of suction line will not work. Basically putting in a big oil trap.

    Who says your ducts are adequately sized for a three ton? What are the sizes? How many supplies and returns and their sizes? What is the static pressure on the current system?

    The one who said it would be fine was telling you to leave the lineset sizing as is...
    Quote Originally Posted by rske View Post
    Thanks for the quick response. 3 response so far, 1 says: No won't work. 1 says: Should be fine. 1 says: Duct size? The air duct system is oversized, good for more than 3-tons. I guess I'm looking for a response with some science behind it as to why it will work or won't work.
    Robert S
    Sent from my SM-G965W using Tapatalk

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  11. #8
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    Keep the 3/4” what size is the liquid line? Why 3 ton and not maybe 2.5 ton?

    What does the install guide of the outdoor unit recommend for different tonnage and length of run and lift course once you figure out the load calculations.

  12. #9
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    Quote Originally Posted by rske View Post
    Thanks for the quick response. 3 response so far, 1 says: No won't work. 1 says: Should be fine. 1 says: Duct size? The air duct system is oversized, good for more than 3-tons. I guess I'm looking for a response with some science behind it as to why it will work or won't work.
    Robert S
    Who said that BS!

    I’ve never seen duct work oversized, it MUST be matched to the airflow the equipment attached to it!

  13. #10
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    What 3 ton unit do you have with a 7/8" line? Most are 3/4", which should be fine. Don't do the 1-1/8" thing, as was pointed out it'll just trap oil and cause you problems.

    Also, what drive size is your furnace/indoor unit? Is it large enough to accomodate 3 tons? A 3 ton unit hooked to a furnace wirh a 2 ton drive will never work properly. If it is large enough, do you have enough ductwork (especially return)?

    It sounds like you're just slapping in a bigger one because the 2 ton didn't cool like you wanted. I'd suggest having someone do a load calculation and size the unit properly, and then verify your ductwork is properly sized or how many runs you need to add.

    If you just slam it in you'll have even more problems and it still won't cool right. You're spending a lot of money, spend a tad more and get someone who knows what they're doing to help you.
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    Statements made by me are strictly my opinions and do not reflect the opinions of my employer. I am not authorized to make any official statements on behalf of my employer.
    Any technical advice offered by me is for educational purposes only, all HVAC related repairs should only be attempted by qualified personnel.

  14. #11
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    Thread Starter
    THANKS FOR ALL THE HELP

  15. #12
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    Most of the time a size lower is a minimal loss of efficiency, like less than 5%.

    Changing from one size to another and back is unnecessary in almost ALL situations in residential split systems.

    As for the ductwork, it needs to be measured and not just eyeballed/assumed to be okay.
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