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Community and Q&A

Recommendation for whole home mini split?

BenRoss | Posted in General Questions on

Hey GBA community,

I’m picking up a 1950’s fixer in Bend, OR (zone 5) that will be a personal home but eventually become a rental.

It’s a 3/2ba about 1400ft single level and I’d like to run ceiling cassettes thru the entire house to both heat and cool. 

Any recommendations for designing this system as well as what manufacturer to use? 


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  1. carsonb | | #1

    Hi Ben, Welcome tp Bend:). First you want to do a “manualj”. GBA has articles on who can do that, one would bee energyvangaurd, but you can also use something like coolcalc for free. For such a small home, honestly you will probably be oversizing it even with a relatively small unit. I’ve gotten reasonable quotes from bend heating. Note that you will want a cold climate condenser that doesnt drop efficiency in the winter.

    1. BenRoss | | #2

      Thanks Carson, do you live in Bend now? I grew up here.

      Feel free to DM me on facebook if you'd like to connect.

  2. walta100 | | #3

    The ceiling cassettes are applying but remember they often have ductwork attached so you are no longer ductless and the equipment and all too often end up with equipment and ducts located in an unconditioned attic, an extremely bad idea.


    1. BenRoss | | #4
      1. DavidfromPNW | | #8

        We use these in our home. We have four cassettes in the common areas and wall mounts in the four of the five bedrooms.

        LOVE the cassettes. We have the on wifi so we control them with our phone. They are just amazing. I can't help you with the size, we have a 4300 Sf home and run two, four head systems.

        Cassettes are the way to go. More expensive but man do they work well.

        1. vap0rtranz | | #9

          >eventually become a rental.

          I wouldn't rent with minisplits. After a brief -- not brief enough -- dabble in passive income as a landlord, American tenants can be fussy folks.

          Americans are not familiar enough with these systems ... I even struggle with my live-in Partner on our own minisplit unit. Details like: having to point a remote at the head (b/c they're infrafred), you can't take a remote and point it at a different head (they're head specific), don't expect one head will heat the whole house, don't do setbacks at night (the 'always on, set-and-forget' of minisplits), and you cannot have one unit cooling while another is heating (for multi-split systems), etc.

          Unless you get a central thermostat that controls all the heads and appears like a "normal" HVAC system to your tenants (Sensibo, Ecobee, etc. 24V low voltage interface), you'll probably have fussy tenants calling you at all hours of the day ... and night. :)

  3. Expert Member
    Dana Dorsett | | #5

    >"It’s a 3/2ba about 1400ft single level and I’d like to run ceiling cassettes thru the entire house to both heat and cool."

    What is meant by "...thru the entire house ..." here?

    The minimum output of even the SMALLEST MLZ (-KP09NA) is a whopping 8100 BTU/hr @ +47F , and since they can deliver 12,000 BTU/hr @ +5F, just TWO of them has more capacity than your likely whole house heat load at Bend's +4F outside design temp, assuming you have some fluff in the walls, glass in the windows, and otherwise reasonably tight.

    If you hang them on the less efficient non cold-climate version of the compressor you get a lower minimum modulation @ +47F, but only half the output at +5F, which would not be advisable in your climate. That would take twice as many MLZs to cover the design load, which leaves you back where you started for the minimum output @ +47F:

    A single right-sized MLZ for the open space, and a ducted solution for the doored-off rooms is probably a better fit.

    Is this house a slab-on-grade, crawlspace, or full basement foundation?

  4. BenRoss | | #6

    Crawl space.

    That makes a lot of sense Dana, thanks a lot!

  5. Expert Member
    Dana Dorsett | | #7

    If there's sufficient head room in the crawl space for ducts, converting the crawl space into an insulated conditioned crawlspace would allow running it as a single zone on a right-sized ducted mini-split.

    IRC 2018 code-minimum for climate zone 5 is R15 continuous insulation, which could be 2.5" of foil face polyiso or 3" of 2lb fiber faced roofing polyiso secured to the foundation with 1x4 strapping, onto which half-inch wallboard (painted or unpainted) would serve as the necessary timed thermal barrier to meet fire codes, or 2.5" of fire-rated Dow Thermax fire-rated polyiso (price it out both ways.) Any vents would have to be sealed over, and a ground vapor barrier installed, sealed to the foundation before installing the wall foam.

    In order to pick a solution the room by room & whole house heat load numbers need to be calculated. (Manual-J , I=B=R, or similar is good enough.) But a 1.5 ton PEAD duct cassette married to a KA18NAHZ compressor would probably cover the design load if you're tightening up the place:

    It might still need a "toaster" resistance heater downstream of the supply plenum or some other auxiliary heat to handle the extreme cold days.

    There are other possibilities. Build yourself a spreadsheet for running an IBR load that can be quickly updated with "what if..." improvements to the building envelope. Be sure to sub-total the room loads, and break down the loads by assembly type (wall area, ceiling area, window area, etc)


  6. jameshowison | | #10

    The MLZ units are good but do consider how level your ceilings are, the units can only be out 1/8 inch over their length (more than that and leaking water is probable, I've seen it happen).

    The air-sealing seal of the register covers is very thin, so if your ceiling is out of level at all (level, not flat) you will be adding the sort of sealing foam sold at home depot, fairly unsightly! Or your blower wheels will get covered with dust and become noisy and unbalanced. (Mitsu claims some sort of new blower wheel coming with a coating that won't hold the dust, but then where will the dust go?)

    A better solution will be to create a level fur-down (use a plane or shimming pieces of wood) for the register cover to seal to, then floating out drywall compound far enough to make the transition invisible (could be 18 inches, if your ceiling is like 3/4 inch out of level)?

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