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Choosing the Right Minisplit System

Dave421 | Posted in General Questions on

Hello, I am new to GBA and I am looking for some advice
on mini split options. I have been researching the different units
and installations and would just like some input on what
those with more experience feel would be the best way to go.
I had a few contractors look at my project and they all seemed
to have very different ideas on sizing and installation which
added to my questions. I am thinking of doing most
of the work on my own with a friend who is an HVAC
tech.

I would like to stay away from the wall mounted units. So
my thoughts were a floor mount for the one large room and
a ducted unit to cover two smaller rooms. I have looked at LG
units and it seems you can also duct off of their ceiling
cassette units. I thought this may also be an option. So on my floor plan
I was going to try and use a floor mount in position A. My concern
is the cfm on the unit is 388 cfm and the room is 35’ long.
Would this be sufficient for the length of that room?
I will also have a wood stove on the other end. Unit D
would be the concealed duct unit in an unconditioned
crawl space. Or the cassette unit with a duct to the bedroom.
Unit C would be the outdoor condenser.

These are the numbers I got using an online calculator.

Front room/kitchen – 368sq. ft. cooling, 8100 btu, heating 10,500
Bedroom- 313sq. ft. Cooling 2600, heating 4200
Living room- 675sq. ft cooling 9900, heating 13,100
Total- 1356 sq. ft.
I am in climate zone 5A

Any suggestions or advice is greatly appreciated!
Thank you

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Replies

  1. Dave421 | | #1

    Just checking if the mini split experts had any thoughts on this?

    Thank you

  2. kyle_r | | #2

    Is the closet next to the bathrooms up for grabs? Could you steal some of it to put either a Fujitsu or Carrier slim duct unit that can be mounted vertically like this? https://www.greenbuildingadvisor.com/article/getting-the-right-minisplit

    Have a central return to the living room. A very short supply run to the living room and bedroom and then run a duct in a soffit through the bathroom to the kitchen.

    What online calculator did you use? Your loads look high.

    1. Dave421 | | #4

      Thanks for the reply, Kyle. I don’t think the closet is up for grabs,
      doubt I could win that battle as we have limited closet space.
      But that is a good suggestion. I didn’t know they could be mounted like that.

      As far as the calculator I used one from the ecomfort site. It seemed
      pretty detailed for all the information you could enter. The front room
      of 368 sq.ft. and the north wall of the bedroom is old construction with single pane windows and only R13 or so insulation. So maybe they came in at a higher load.

      I added a rough look to my floor plan of how I thought the duct could run if I have to
      go with the concealed unit. The unit would be in the crawl space in the middle
      of the two rooms. Runs are 8’ to 12’. 6” flex duct into
      6x10” vents. With the red boxes being a return in each room going straight up
      to the return plenum. Maybe a 10”x10” return box? Any thoughts on this?

      Maybe I am way off base on this. I have just be trying
      to do research on my own and talking to a few friends about it. There is
      a lot more involved than I realized.

      Any suggestions are much appreciated!
      Thanks

  3. jameshowison | | #3

    One thing to consider with a "multi-split" (ie multiple heads on a single outdoor compressor) is the over-heating/over-cooling possibilities. Check out https://www.greenbuildingadvisor.com/article/multi-zone-heat-pump-issue as a starting point.

    When the outdoor compressor is selected, be conscious of the minimum output levels, think about how that production will be divided between the indoor units. This is particularly a problem if the loads are unbalanced due to sunlight through windows or woodfires that only run sometimes.

    If there's any chance of using 1-1 units I would definitely price those out, it's definitely not the case that multi-zone is always cheaper. Especially your "A" unit seems a candidate for a 1-1 system (if there is a possibility outside the wall there).

    Finally, if considering ducted then don't get exclusively focused on the "slim-line" "concealed" "pizza box" or "horizontal ducted" units, also check out the "multi-position" air-handler units. These are the small versions of the traditional air-handlers and they can be quite small. They also service from beside the unit and not underneath the unit. e.g., for Mitsu the 12k btu/h SVZ-KP12NA measures 17 x 22 x 40 where as the slimline one measures 39 x 28 x 8 ... but the 8 dimension is deceiving because service requires ~24" under the unit (directly, or disconnect all ducting and raise). Also adding filters etc for the slimline requires creative duct building.

    http://www.mylinkdrive.com/USA/M_Series/R410A_Systems-1/Indoor_Equipment-3/Multi_Position_Air_Handler-2/SVZ_KP_NA_Models/SVZ_KP12NA?product

    Also consider whether you want to clean three filters and risk three different units making noises if they get dust in their wheels :)

    btw, take these just as things to ask around about, I don't do installs just suffered through figuring this out with a multi-zone install in my house that we had to convert to a central ducted system due to multiple issues. So I read a lot of stuff here and on hvactalk.

    1. Dave421 | | #5

      Thanks for replying and sending the links, James. The multi zone discussion was
      very informative. I didn’t realize multi-splitsystems would have those issues.
      I would only have two units so I guess I didn’t think that would be too bad. A few contractors I had look it over suggested 3 indoor units on 1 condenser. I don’t think another
      condenser near the A location to get 1-1 system will work out.

      I looked for the minimum output levels on the Lg condenser but couldn’t find
      anything on it. Hopefully I can find something. I had been wondering what affects using the wood stoves would have on the system. I will also look into the air handlers
      you mentioned.

      Thanks for sharing what you learned through your own experience.
      I also have been reading as much as I can here. I had a few contractors look
      it over and they all had very different ideas and sizing figures so it
      just added to my confusion. Also their prices were pretty shocking.

      Thanks again for your help!

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