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Thread: Line set sizing

  1. #1

    Line set sizing

    OK so I have found a decent deal on a Heat pump + install.

    The only issue I have is that this contractor is recommending a 3 ton unit versus others that recommended a 2.5 ton, however this is the company who has been installing the HVAC for my particular builders homes for the last 4 years so he is very familiar with my exact model home and its requirements, so I'll trust his judgement on that.

    The issue is with the line set that was installed during the construction of the home. It has a 3/4" Suction line and 3/8" liquid line. According to the specs for the heat pump he's installing it requires a 7/8" suction line. Is the 1/8" smaller diameter suction line a real issue? Should I have him redo my line set? Maybe trade on mine? or will it be fine to go ahead with everything as is? Or should I go for a 2.5 ton unit, which was suggested by about 75% of the quotes I got and matches my line set?

  2. #2
    Join Date
    Dec 2006
    Location
    Northern VA
    Posts
    389
    Get a heat load calc done and you will answer the question otherwise it's all just a guess.

  3. #3
    Join Date
    Apr 2008
    Posts
    65
    Nick,

    A heat pump can be over sized up to 25% over the cooling load to give better heat in the winter. A load calculation by room is still important to get the ducting right as well as to size the heat pump correctly.

    An over sized heat pump may not dehumidify as well as the smaller size. Is it humid in the summer where you are? There would not be a problem in Arizona, but a big problem could exist in Florida or Houston.

    The eighth of an inch reduction on the suction line will reduce efficiency slightly, but the manufacturer's data on the reduction should be consulted. The reduction may or may not be allowed. If it is allowed it might reduce efficiency 3-5%, but who knows till the manufacturer's data is consulted.

    Bill

  4. #4
    Excellent reply MrMcGoo, very helpfull.

    I consulted with the contractor and he assured me that under 60 ft of Line set there is no issue, and a change is not required.

    As for the tonnage, all load calculators and rule of thumb estimates put my need at 2.8 tons. Most recommended undersizing that, but a few did recommend 3 ton. This contractor also has many years experience dealing with my exact model home, so I'll take his word on it and go with a 3 ton.

    Yes we live in a humid climat, but northern (Montreal, Canada) where heat + humidity are an issue for a short time in the summer. The heat pump will surely be heating more than cooling in our home.

  5. #5
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by NickDarios View Post
    Excellent reply MrMcGoo, very helpfull.

    I consulted with the contractor and he assured me that under 60 ft of Line set there is no issue, and a change is not required.

    As for the tonnage, all load calculators and rule of thumb estimates put my need at 2.8 tons. Most recommended undersizing that, but a few did recommend 3 ton. This contractor also has many years experience dealing with my exact model home, so I'll take his word on it and go with a 3 ton.

    Yes we live in a humid climat, but northern (Montreal, Canada) where heat + humidity are an issue for a short time in the summer. The heat pump will surely be heating more than cooling in our home.

    for proper cooling and heating, i wonder why any contractor would even consider undersizing a system

    these days there are v.s. motors to get rid of extra humidity!



    .



    .

  6. #6
    They all said it's preferable to undersize to avoid short cycling, but honestly from a need of 2.8 to an actual 3.0 it's pretty damn close!

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,824
    The line set might cut you back to the 2.8 ton. Then you'll be sized just right.

    Line set shouldn't be a problem.
    Contractor locator map

    How-to-apply-for-Professional

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

  8. #8
    Thanks beenthere....now I feel even more comfortable with my decision.


    The heat pump is an Amana ASZ140361 (http://www.amana-hac.com/Home/Produc...1/Default.aspx). Do you have any comments about this machine? I know it's not high end on but the warranty is pretty good!

  9. #9
    Join Date
    Apr 2007
    Posts
    6,285
    3 ton @ 75 ft and 3/4" pipe there is a .9 capacity multiplier....@ 50 ft it's .93

    With 7/8" it's .96 and @ 50 ft it's .98

  10. #10
    It's only around 40' of pipe....

    Would that mean that you multiply the capacity 3 ton * .9 = 2.7 ton?

    And it 40' what is the multiplier?

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,824
    Its a good unit. Has a good warranty, don't for get to register it.
    Contractor locator map

    How-to-apply-for-Professional

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

  12. #12
    Join Date
    Apr 2007
    Posts
    6,285
    Quote Originally Posted by NickDarios View Post
    It's only around 40' of pipe....

    Would that mean that you multiply the capacity 3 ton * .9 = 2.7 ton?

    And it 40' what is the multiplier?
    I revised my OP for 50 ft also....I got confused with another thread. It only starts @ 50 ft so I would think it would be slightly higher with only 40 ft than @ the 50 ft capacity multiplier.


    LOL about what been there said exactly.

  13. #13
    OK thanks...and I won't forget to register it...that's for sure!

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