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Mitsubishi recessed four-way ceiling cassette in unconditioned attic

Edd R | Posted in Energy Efficiency and Durability on


I’m about to install a whole house minisplit system as part of a home remodel. Our attic is unconditioned and we are planning to install Mitsubishi recessed 4-way ceiling cassettes (SLZ-KR units). Note that the are ductless. They are NOT ducted minisplit concealed units. 

Do I need to build a conditioned box around each unit in the attic, so that their body won’t effectively be in unconditioned space? Or do I just need to make sure that they get installed properly (air sealed) and that there is no insulation gap around them (and it’s ok if the top of the ceiling cassette is directly exposed to the unconditioned space)?

Thanks in advance for your help. 

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  1. Expert Member
    Dana Dorsett | | #1

    I've never heard of the SLZ- KR series- was that a typo or is it something brand new? (SLZ- KA, SLZ-KF. and the 1-way SLZ-KP are what I'm more familiar with.)

    Air sealing is important, and if you can adequately air seal around the perimeter of the cassette, great, but it's still important to insulate over top of the cassette, particularly in snowy climates, since the heat leak out of the top can otherwise start ice dams. Stacking high density batts for eases of service is sufficient (assuming air tightness at the ceiling plane)- no need to build an air tight insulated dog-house over it.

    1. Edd R | | #2

      Thank you Dana for helping. Yes, that was a typo! I meant SLZ-KF!

      Thanks again.

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