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Tips for insulating and sealing around mini-split flare connections?

BenWilson | Posted in Green Building Techniques on

Any tips for how best to seal and insulate around the flare connections off the indoor unit? For wall-mounted units both lines are usually run by the manufacturer though a shared insulation sleeve that is split near the end to make the flare connections. From there the linesets are individually insulated. I’ve always had trouble sealing and insulating this transition from shared insulation to individual insulation. I usually just wrap a ton of insulating tape around the whole area, but this always winds up looking sloppy and it still sometimes fails with air sneaking in and condensing.

Anyone out there have a better way?

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  1. Expert Member
    BILL WICHERS | | #1

    If you sleeve the wall first, so that the lines are passing through a short piece of pipe and not just going through the wall unprotected, you can use canned foam. Wrap some good electrical tape (the 3M stuff that comes in the little plastic cans for around $2-3 per roll) sticky side out around each pipe separately through the entire distance that will pass through the sleeve. Make a cardboard or thin wooden plate to temporarily cover the end of the sleeve, and put a sheet of waxed paper over that. The easiest way to make the cover plate is to cut it big enough to completely cover the end of the sleeve, then drill holes where the two refrigerant lines are. Cut the plate in half through the center of both holes so that it can be placed over the end of the sleeve with the lines in place.

    Once this is done, fill the sleeve with canned foam while the cover plate is tightly fastened over the indoor end of the sleeve. The cover plate will ensure a flat finished indoor surface to the canned foam to make a permanent cover easier to install. The wax paper makes the temporary cover plate releasable so that you can easily remove it after the canned foam has set. The “sticky side out” electrical tape will allow you to cleanly remove the canned foam from the line set in the future if you ever have to do that (you’d still have to chip the canned foam out of the sleeve, but the tape will prevent it from adhering to the line set so you won’t have a have any issues with cleaning the lines off in the future).


  2. Expert Member
    Akos | | #2

    This is not an easy connection on wall mounts. It doesn't take much to have it drip there.

    Make sure the tandem sleeve covers at least a couple of inches over the insulation on the lineset. Tape the slit of tandem sleeve closed then spray a bit of canned foam into the gap at the transition. Continue to wrap the tape past over this section and onto the lineset. The tape will contain the expanding foam allowing it to seal the transition.

    Make sure to use closed cell foam tape, some of the fiberglass insulation tapes don't have a proper vapor barrier.

  3. 1869farmhouse | | #3

    I agree with Akos, the smallest gap will drip. I generally do the same thing and run the line set through pvc/fill with canned foam. The only thing I add is capping the outside end with duct seal compound. Canned foam can be an iffy air seal, but the clay type duct seal is 100% and provides a solid “stop” for the foam.

  4. BenWilson | | #4

    Thanks guys. I've had luck using foam and duct seal for the through-wall penetration, usually through pvc (i've tried the telescoping sleeves too). The part where I have had trouble is on the outside of the wall where the lines split from tandem insulation to individual insulation. I'll try Akos' suggestion to spray foam the transition area inside the tandem insulation; my read is that this treats the taped tandem insulation kind of like a sleeve itself that you fill with the foam.

    I realize that condensation on the outside of the wall isn't always too big of a deal. But I still worry that condensation here might:
    1. Degrade the insulating value of the pipe insulation
    2. Degrade the copper and flares over time (I usually get the green/blue staining when I find condensation problems)
    3. I've had some installs where the indoor unit is hung against a garage wall and the lineset passes through a garage before going outside. In these cases the condensation could occur in the garage and cause dripping problems for the homeowner.


  5. Expert Member
    BILL WICHERS | | #5

    Note that duct seal dries and hardens over time, so you need to check it periodically. In my experience, it's good for around 10-20 years or so before the seal starts to fail and you need to replace the material when used outdoors.

    The condensation shouldn't be a problem for the copper pipe. Some slight discoloration isn't usually a big deal. I have seen decades old line sets (on conventional air conditioners) with split or missing insulation and discolored pipe but no damage or noticeable thinning of the copper tubing.

    In the telecom world, where we have lines that might cause condensation issues that we can do nothing about, we put a tray underneath to catch any drips and safely drain them away. You can retrofit some vinyl rain gutter of the "U" style for this purpose. It's a bit of a kludge, but it keeps the drips from causing problems with finished surfaces.


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