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mitsubishi mini split branch box required or not

Hi all,

I am working with few vendors and want the mini splits to be installed as primary heat option. I would have back up electric heat baseboard but planning to use mini splits in Massachusetts as primary heat for now.

my home have 3 bedrooms upstairs and 1 living room downstairs. and system i want to work is like below:

Living room is on first floor, master bed room is directly above it and then 2 small bedrooms are 40 feet from master bedroom which could be connected via unfinished attic.

We got quotes to install following:
2, Mitsubishi, M- MSZFH06NA, 6,000 BTU, wall-mount air handler
2, Mitsubishi, M-MSZFH12NA, 12,000 BTU, wall-mount air handler
1, Mitsubishi, M-MXZ4C36NAHZ-U1, 36,000 BTU, multi-zone heat pump condensing unit

Now here is the difference 2 contractors say we need to have mitsubishi pac-mka50bc branch box for 4 head installed and 2 are saying we dont.

I called mitsubishi and they said with the model MXZ4C36NAHZ i must have that but you could get away with it. So it was more confusing.

I want to know is do i really need branch box or i can get away with it? as difference in quotes is $$$$ difference.

Thank you all in advance for your help.


  • HVACNUTHVACNUT Member Posts: 3,358
    Is this a City Multi system?
    You're showing 5 heads for 4 rooms and 60,000 BTU's. What's special about the MXZ?
    There has to be a reason its spec'd.
    Is your mind made up on the Mitsu? If so, why?
  • GWGW Member Posts: 3,756
    Im a Mitsubishi guy, seems like they didn’t explain it very well. They are all correct

    Mitsubishi “also” has a non “d box” 4 zone model, we are installing one today. If you see an “HZ” in the model number, that’s their hyper heat models, and the 4, 5 and 8 zone will have (require) a box (and no, it’s not optional). D box installs are much more costly.

    Non hyper heat- I think the 5 zone requires a box. Don’t know off the top of my head.

    If you don’t need high performance heating save the dough and get the “regular” 4 zone. They still heat very well. Plus the 4 zone hyper is a “double decker” as we call them, it’s a very big unit

    Some installs would require a d box if you have long lines ruining all over the place. That’s the draw back of the “port style” outdoor unit, there are stiffer limitations on the line lengths. With a box install you can go much further with the piping.

    If you ever pop a leak on a d box system, best of luck, gonna be a whole day for a basic repair
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • munuleomunuleo Member Posts: 2
    Thank you for explaining. This is for home and heat is primary concern. Current spec for “double decker” is 36000 BTU. It does have HZ in model name so not sure why 2 contractors said they don’t need branch box. From your response I might just go with non branch box install to avoid confusion and future headaches. May have 2 outside units on each side then having one big unit with 4 heads.
  • GWGW Member Posts: 3,756
    Makes sense; we actually prefer two smaller systems vs a big double. Actually I like singles the best: most efficient, super low turn down ratios (very low BTU outputs)

    Maybe a single for the living room and a triple for the beds? All sorts of ways to do this

    There must be some glorious confusion though, your Mitsubishi people are saying they’re gonna sell you a hyper heat 4 zone and a box isn’t needed? Wow——best of luck to them fellas.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
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