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Community and Q&A

Opinions on 4-Way Cassette-Style Mitsubishi Mr. Slim

arnoldk | Posted in Mechanicals on


I am leaning towards getting the Mitsubishi Mr. Slim M-series heat pump for the two-story house I am currently building. I notice they have these 4-way cassette style unit which I’m thinking may work well to more evenly distribute the air on the main floor.

Does any one have experience with this or know of any drawback to them?


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  1. Expert Member
    Dana Dorsett | | #1

    One down side to the 3- way cassettes is that they don't really fit between 24" on center joist spacing. At 22-7/16" wide it's enough slop to work with suspended ceilings, but not in the 22.5" nominal spacing between 24" on center joists.

    The modulation range is also pretty limited- only about 2:1 even when married a dedicated SUZ.....NAHZ cold climate single zone compressor, and about 3.5: 1 married to a non-cold climate SUZ.....NA (no -HZ) version, let alone on multi-split compressors.

    With low turn down ratios it become super important for comfort & efficiency to NOT oversize them, or they'll be cycling all the time, never modulating.

    The equivalent Fujitsu AUUxxRLF four way cassettes have the same framing crowding issue, but all sizes will crank down to 3100 BTU/hr @ 47F (and 3100 BTU/hr @ 95F in cooling mode) when on dedicated AOU-xxRLFC single zone compressors.

    1. arnoldk | | #3

      Hi Dana,

      Thank you for that information which I'm sure partly explains why they are not commonly found in residential. I was just informed that in my case the I-Joist will be 16" O.C. which these will note work.

      Do you recommend to simply stick with the typical Wall-Mounted Style unit?
      Is there one company (Mitsubishi, Fujitsu, LG...) that you recommend in terms of overall efficiently and reliability?

      Thank you,

  2. Expert Member
    AKOS TOTH | | #2

    You can also look at the LG units.!/product/33657

    The nice feature with these is the knockouts on the side which are for transfer ducts. These lets you divert 50% of the flow to other areas of the space for more even heating.

    1. arnoldk | | #4

      Hi Akos,

      I will check that out since we have a rec room that is closed off from the rest of the main floor which also happens to be on the north side. I wonder if wall there is something similar for wall mounted units?


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