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Community and Q&A

Is there a risk of mini split line sets sweating / condensing when run through an attic?

michaelbluejay | Posted in Green Building Techniques on

(1) Should I be concerned about sweating / condensing of insulated mini split line sets buried in loose cellulose insulation run through an attic?  An attic is the last place you want loose water.

(2) Either way, can I simply run the line sets through PVC pipe to eliminate the risk?

I’m planning a DIY install of a 5-head mini split in CZ-2.  I’d prefer to run the line sets through the attic, because running them outside the house will triple the line length, and they’d look ugly as sin on the house.  I could mitigate the ugliness by running them straight to the ground and burying them for the run around the perimeter of the house, but I’d still have the problem of a super-long run.

The line sets will be wrapped with pipe insulation, and then buried under many inches of loose-fill cellulose, but I don’t know if that’s enough to eliminate condensation risks.

Seems like I could just run the line sets through the attic in PVC pipe, and eliminate the risk of condensation.


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  1. gusfhb | | #1

    Insulation should prevent it

    I wouldn't install a multi head unit on a bet. Too many downsides with professional installs, no less DIY

    1. michaelbluejay | | #2

      You convinced me. I checked and the price penalty for 5+5 compared to 5+1 isn't that great. Also, with 5 condensers, if one breaks down, then 4/5 of the house still has heating and cooling. I didn't want ugly condensers on the front of the house, but I'll just build an attractive wall in front of them and then it'll look fine.

      1. gusfhb | | #3

        I would read the commentary here about multi splits
        Consider ducted split units

        1. Expert Member
          Michael Maines | | #4

          I've had several conversations with knowledgeable HVAC pros lately about the multi-split issue, and all seem to think that multi-splits can still be a good choice, as long as the indoor heads are serving rooms with similar loads. It's when the indoor heads are serving rooms with different loads that efficiency drops off. I'm not sure they're correct, it's just what I've heard.

          1. Expert Member
            Akos | | #5

            Interesting tidbit one of the posters here mentioned is that some of the multi splits (ie Daikin) have the option of derating the outdoor unit through jumper settings, this can at least get it closer to actual load for 5 rooms.

            This should get better operation of the multi but still won't solve the indoor head oversizing issue or problems with refrigerant bypass if only one or two heads are calling for heat/cool.

            Overall, a slim ducted unit with short ducts to each room is the much better option. Cheaper BOM cost, higher efficiency, WAY less maintance but it is a more complicated install. Putting in 5 wall mounts is no simple job either.

            If this feels like too much work, some of the 4 way ceiling cassette units can have jumper ducts installed. You could mount one in the hallway ceiling and run the ducts to each bedroom.

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