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Community and Q&A

Mitsubishi HyperHeat Install – Line set extension

DoradoRenovate | Posted in Mechanicals on

I am installing a 30k Mini-split Mitsubishi Hyperheat system in a wood framed condominium as part of a remodel.  The challenge I am facing is the distance from the ceiling cassettes (3 of them) has increased due accomodating an obstruction in the routing path.  I have already purchased the line sets and the distance beyond the length of the linesets is approx 6 (six) feet.  I am interested to get input on if it is permissable(code) and/or advisable to extend the current linesets with an additional short section of line set piping connected utlizing flared fitting connections.  ie…one added flared fitting connection to each line set.  I am well under the maximum allowable line set lengths.  One run is approximately 56′, the other two (2) are in the range of 42′ in length each.  Climate zone is 4C

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  1. [email protected] | | #1

    A pro would braze here. Flare couplings raise your risk of a leak but can work. I'd make sure the couplings remain accessible for service, use beefy refrigeration flare nuts (not the lighter gauge ones for lower pressure applications), use an orbital action flare tool, lubricate the nuts and flares with nylog, use a torque wrench according to specs, and wrap the joints in pipe insulation.

    Also make smooth tubing bends, follow install instructions on nitrogen pressure testing, evacuation, and weighing in additional charge and you should be fine.

  2. DoradoRenovate | | #2

    Thank you for input, very much appreciated. I just want to be sure to do it right the first time.

  3. Jon_Harrod | | #3

    Agreeing 100% with Norman's comments. Brazing (while flowing nitrogen to prevent oxidation) is definitely preferable. If you do end up using flare couplings to extend the linesets, and the linesets run some distance on the outside of the house, put the couplings there, where they'll be easier to access.

  4. DoradoRenovate | | #4

    thank you Jon for your advice. As I am learning more regarding this subject, if you use a coupling other than brazing, is it just good practice to locate the coupling where it is permanently accessible ( to crawl space or exterior) or behind an access panel if within a finished space, or does code specifically require the accessiblilty?

    1. Jon_Harrod | | #6

      I believe either of those would be acceptable by code. But as Akos mentions, you would be doubling the number of flare connections for those linesets, hence doubling the chances of leakage. When you add in the extra costs of fittings and possibly an access panel, plus the increased likelihood of callback, the overall math favors brazing/replacing over flare couplers. Clean, properly stored linesets can be sold or used on another job.

  5. Expert Member
    Akos | | #5

    You are installing probably around $5k of equipment. The cost of the proper length line set, even with today's high copper price is small compared to the issue with refrigerant leaks. Multi splits are very sensitive to refrigerant volume, it doesn't take much loss for the efficiency to start nosedive.

    The extensions double the number of flare connections, since all flare connections leaks (even when well installed and torqued), you are just asking to have trouble with low refrigerant down the road.

    Now is the time to get it right, either get the correct length line set or braze.

  6. 1869farmhouse | | #7

    I have to disagree with some of the above comments. Mitsubishi specs call for flares, not brazing. Mini-Splits are a whole different animal. Use the flares with the flare nuts provided and torque to specs - you’ll be golden.

    1. Expert Member
      BILL WICHERS | | #8

      Their specs are likely assuming you're making the connections to the units. If you're making a splice in the lineset somewhere, brazing is really the proper way to do it. Mitsi's specs are not going to be concerned with a splice somewhere along the line, they're only going to be concerned with how you connect to their units.

      There has been an upward trend in refrigerant prices for some time. I have lots of equipment using R22, for example, and that has gotten VERY expensive. Saving money with a potentially leaky splice could very well cost you a lot more in the long run when refrigerant recharge is needed.


      1. 1869farmhouse | | #9

        From what I understand, and I’ve installed multiple Mits minis now, the concern and the reason they specifically advise utilizing the flare fitting instead of brazing is the concern for contamination. Even with proper nitrogen use, these units are just so much more sensitive to the tiniest contaminants I personally don’t think the risk outweighs what would be gained.

  7. joshdurston | | #10

    I have to agree with Akos that the right thing would be to just get the proper length linesets, and skirt the issue entirely.

    IMHO, if I had to extend I would braze keeping in mind the risks with not doing it properly.

    Take careful measurements, so you aren't guessing in the future.

  8. DoradoRenovate | | #11

    Many thanks to everyone whom has provided their expertise/experiences and just as important their opinions. I sincerely appreciate the sharing of your knowledge.

    I have one additional question regarding installation and accessibility of the line sets (gas/liquid) in a finished wall or ceiling assembly. In simple terms, does anyone have some words of advice/wisdom/"tricks" of the trade regarding linesets et al installed in wood framed wall/ceiling assemblies.

    I will be installing servicing/maintenance panels as per Mitsubishi's specs at the ceiling cassessettes, as well as, careful line set routing to assure proper radius of the copper tubing, drain slope, etc...

    The installation I am undertaking is a remodel so the routing is thru numerous interior finished areas (the ceiling is 2x12 joists for the second floor above and the walls are 2x4 if that helps illustrate the environment) before I can reach the crawl space. Therefore, I will be opening up the ceiling and walls to run the line-sets, condensation drains and associated electrical/communication. In my situation, an exterior wall penetration is not possible until I reach the condensor unit. Again, many thanks to everyone for their posts.

    1. Expert Member
      BILL WICHERS | | #12

      Be very careful anywhere you rigidly attach the line sets near any part of the system that vibrates. I have seen rubber covered P clamps gradually wear through a copper refrigerant line and cause failures before. Once the line gets farther away from any powered parts of the system this shouldn't be a problem. DO NOT use excessive clamping force on the lines, you don't want to damage them. I like the rubber lined P clamps for this purpose, or two hole pipe stamps and a piece of 1/8" thick EPDM rubber sheet to protect the lines inside the clamp.

      If you do use flare fittings to couple the lines together, make sure you put that coupling someplace accessible so that you can leak check it periodically.

      It is sometimes advantageous to run a conduit sleeve and run the linesets through that sleeve instead of running the linesets through holes by themselves. The sleeves offer physically protection, make any future replacement easier, and often make it easier to get a good air seal too.

      Absolutely make sure the outdoor unit is mounted on a stand away from any bedrooms! There have been numerous threads on here about people going crazy because of the vibrational noise. A stand on a small concrete pad and a loop in the refrigerant lines before then enter the structure will drastically reduce the amount of vibrational noise transferred to the structure.


  9. Expert Member
    Akos | | #13

    Make sure both lines are fully insulated without. Any exposed copper will sweat inside your wall and cause a lot of issues.

    The lines also expend and contract a fair bit especially when going into defrost. Make sure the lines are sleeved when they go through any studs/bottom plates and also add the occasional jog for any long straight runs. By jog I mean say you have a 40' horizontal run. Run the first 20', easy 90 bend up about 6" to 10", easy 90 back to horizontal to continue.

    Condensate pumps are quiet but not silent. If the unit is in a bedroom, go for gravity drain only.

    Make sure the unit is charged properly and account for line length. Low refrigerant on these can significantly increase electricity use.

    Make sure the filter grill if well sealed to the unit. These are a pain to clean and without a decent fit the unit will get dirty quickly. Even then it is something that needs to be done every 4 to 6 years, PIA.

    The 30k hyper heat unit has a 3:1 modulation (~11k min when heating). This can be an issue if you have any 6k or 9k heads on it as it will need to bypass some of refrigerant through the rest of the zones when only one head is calling for heat/cool. This hurts your efficiency and sometimes overheats the zones not calling for heat.

    A better setup for most installs is a single slim ducted air handler for all the bedrooms instead of a ceiling cassette in each.

  10. Expert Member
    BILL WICHERS | | #14

    Akos mentioned expansion loops in the linesets. I just thought a picture would help show what these look like. Sometimes pictures are better than words :-) This is just a random pic I found with Google, but it shows the general idea.


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