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Review placement and sizing of mini-splits

Klucas06 | Posted in Mechanicals on

I have been reviewing the submittal sheets along with what feels like endless reading on this site. Through all the reading and studying I feel like I have a decent sizing and placement locations figured out but would like second opinion.

Front door faces NE and I’m in CZ 4A, 24149. The fireplace is a vented gas fireplace that is vented out the adjacent covered porch roof, no chimney. Patio doors where changed to single doors.

Design temps: 17/89. Indoor temp year round will be set at 72.

Some of the concerns are that the locations are near the minimum offset from the ceiling, about 6-8 inches. Will this be a significant comfort issue?

For efficiency and the ability to take advantage of the low min-modulating I’m looking at installing a Mitsubishi MSZ-FH06NA/MUZ-FH06NA combo in the 3 bedrooms and MSZ-FH09NA/MUZ-FH09NA in the Living/dining/kitchen area, 4 separate units.

Would it make sense to get the hyper heat units in my area or maybe just have the FH09 combo?

Thanks for any help and suggestions.

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  1. user-626934 | | #1

    You’d be better off with a pair of small ducted mini-splits.

    Are you building on a conditioned crawl space?

  2. Klucas06 | | #2

    I've tried discussing ducted options with the local HVAC contractors in this area and I haven't been able to get even a remotely comfortable answer from them, one even said that if I would design it then they would give me a quote.

    The house will be on a conditioned Crawlspace. One condition from the wife is that if we have ducts, they have to be in the ceilings.

  3. user-1137156 | | #3

    If you put ducts in the ceiling & keep them in conditioned space you are creating a "service cavity" as your air barrier must be above the ducts. That's my plan being discussed in another thread.

  4. Klucas06 | | #4

    Thanks for the input. I will have an unvented insulated rafter assembly so I would have room to run ducts if I could find a trustworthy contractor. I was mainly interested in the wall units due to their higher efficiency ratings, the thought process I had was with independent systems having redundancy and the capacity during the extreme cold spells.

    Any other options or advice on layout or equipment selection?

  5. Klucas06 | | #5

    After further looking at the ducted unit, it seems that it would be over sized and with the higher min-mod I feel it wouldn't be very efficient in my climate.

    Is the recommendation for ducted units to accommodate the different zones? The reason I was proposing 4 separate units was to be able to turn off 1-2 units during the shoulder seasons. Maybe I'm not seeing what y'all are?

  6. Klucas06 | | #6

    I really appreciate the comments so far. I would rather utilize the wall units. Does it appear to be a way to make it work and still be efficient?

  7. Chris_King | | #7

    Would the upstairs bedrooms doors be opened at night? A single mini split ceiling cassette should be able to cover them assuming the house is insulated and air sealed properly, having a hard time reading the plans to see if there is exterior insulation on my phone. For comparisons im in zone 4A and use a Fujitsu 18,000 btu ceiling cassette to heat about 1,400 sq ft that has to shoot air down the hallway to hit the bedrooms and it keeps up until we hit the teens and I have 2x4 walls with no exterior foam and no cralwspace insulation.

  8. calum_wilde | | #8

    Similar to Chris I'm using a single head per floor, ~1200sqft per floor. I have 2x6 walls with only cavity insulation, and R20 wall insulation in the basement, but no slab insulation, and R60 attic insulation. I'm in zone 6a with a design temperature of 0°F. I'm using a 15LRS3H Up stairs and a 12LRS3H downstairs.

    Even at design temperature there's no issue with keeping the house warm throughout, as long as the interior doors are open.

  9. Klucas06 | | #9


    The upstairs rooms will be the kids (ages 4 & 5) room and we plan to leave the doors open most of the time. Originally I had planned to use a ceiling cassette but the roof trusses are 12-16" oc and won't leave space to mount it now so that's why I'm looking for other options. Do you think a single FH06 or FH09 would have enough throw to condition both the bedrooms and bathroom, it would be about 40' from end to end (about 600sf total)

    The walls are going to be 2x6 with dense packed cellulose, no exterior foam.

    Roof will be 5" of EPS or polyiso with 2x8 rafters dense packed.

    Conditioned Crawlspace and unvented roof. I'm shooting for about 2ach/50.

    Thanks Calum. Are your units centrally located or are they maintaining from end to end?

  10. Chris_King | | #10

    My ceiling cassette shoots about 30’ no problem cause any unevenness eventually levels itself out. Regarding the space not sure if trusses can be cut, I don’t think they can but I’m no engineer. My ceiling was just joists so we cut one to box in the unit and supported the joists on each side to it. Regarding the size I’ll leave that to someone who can do the math better then myself. Just roughly if it’s tight insulated I would assume the 09 would be ok but someone with more math ability should be able to chime in for the second floor.

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