I was looking to do a diy dual mini split unit one condenser 27k BTU 22 seer. Two heads 12 & 18k. One head will be in the garage next to the electrical panel and the run for that is less than 10ft. As the condenser will be on opposite side of the wall. The second head would be about a 60ft run from the condenser. Are line set runs that long a no no? I don’t know if I should do two separate condensers. I’ll then need my electrician to run two disconnects vs one and I’ll have another condenser on the opposite side of the house.

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    – isherwood
    Aug 2, 2022 at 14:43
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    Is your AHJ requiring a separate disconnect for the inside units? The only true DIY that I have seen is a single head. what brand and model is your DIY? You will need to check what the precharged line set max is. Normally 25’ ea head total of 50 you have 70 so a top up of refrigerant would be needed for most systems to function with that much of a line set, long line sets reduce efficiency but if well insulated they work.
    – Ed Beal
    Aug 2, 2022 at 14:54
  • No, single family home. Mr cool 4th gen. Unit. Aug 2, 2022 at 15:26
  • I would install two separate units. Easier for DIY. I would install Mr. Cool for the 18 K home unit. After you complete that install, install in the garage. There are other systems that are a lot cheaper than Mr. Cool that are the same hardware. Once you have some experience you can install one that offers less hand holding. Aug 2, 2022 at 16:53

2 Answers 2


It's more efficient to run electricity a long way and the line sets a short way, so two outside condensers makes more sense for inside units placed far apart.

In general, you can get more efficient units as single-heads rather than dual (or triple or quad) heads (specifically, you'll have to shop and see what you can get, for how much, but that's been the case when I shopped for mine.) More efficient units cost less to run for their whole life, even if they cost a bit more to buy when you buy them.

Your specific unit will have specific limits as to line set length, but a longer line set will contribute to it running less efficiently than the same unit with a shorter lineset.


Mr Cool has couplers to increase the pre-charged line set lengths so you could do (2) 25' + (1) 15'lengths and still be within spec, however, the pre charged line sets are very expensive and more connection = more opportunities for leaks. Once the refrigerant leaks out you lose all the benefit of having them pre-charged in the first place. 2 separate systems is your best option. Make sure you use a torque wrench, and you should have a disconnect at the air handler and condensate switch.

I've installed 2 Mr. Cool DIY systems with great success. These are the best (and only to my knowledge) truly DIY systems - don't let anyone talk you out of going this route.

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