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Community and Q&A

Inadvertent trap in minisplit line set?

DIYJester | Posted in Mechanicals on

I’m finishing the installation of my mini split line sets and realized I may have introduce a “trap” into the line set due to the way I had to route it.

The main line set runs from the compressor to the branch box in the attic. From the branch box, the line sets run down into one stud bay, in a 180 degree bend, through a stud, and pointing back up into another stud bay. This 180 degree bend is my concern.

This was ran like this for multiple reasons. One, I have slab on grade construction where 4/5 heads were installed so I have to run the linesets from the top down. The mini splits are also mounted 8″ from the top of the wall in 3 areas so I would have to bend the line set up and have to ensure it was cut low enough so the flared connection wasn’t in the double top plate. Instead of this I just routed it out slightly then down with the condensate drain.

Would a vertical U shaped loop between the head and branch box cause any issues?

Thank you,

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  1. GBA Editor
    Martin Holladay | | #1

    Good question. I consulted a few installation instructions for ductless minisplits, and I couldn't find any warnings about traps or bends, so your installation may be fine.

    That said, I'd like to hear from GBA readers experienced at minisplit installations for more information on this issue.

    1. Harr1z | | #3

      Hey Martin, I am about to perform an install that will need a 180 bend right out of the indoor unit to run the line in the knee wall area of the attic, which is right above where I want to hang the indoor unit. Have you learned anything new on this problem set? ~Mike

  2. DIYJester | | #2

    Thank you for chiming in Martin. That was the same thing I have come up with as well so far. I would just hate to have to re-run the lines if I burnt up a $2000 compressor because the oil ended up in the loops.

  3. this_page_left_blank | | #4

    A trap like this is actually required for line sets beyond a certain length. It's hard to imagine how it could be required in that case but somehow not be allowed with a shorter line. I could see a problem if the trap was very close to the bottom of the line, but that doesn't sound like the case for you.

    1. Harr1z | | #5

      What about at the indoor unit itself, which will be the lowest point. The line set needs to go up into the attic and run to a condenser on the roof. The line initially flows downward out of the unit and would need a 180 turn to head up from the unit. The other option would be to lower the condenser below the height of the indoor unit, so the 180 wont be the lowest point overall, but will be the lowest point near the indoor unit. thoughts?

  4. willymo | | #6

    My installer routed the line set under a window, then up to the unit. The 'trap" is then at the lowest point.

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