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Mini Split Head Location Question


I'm strongly considering using a ductless mini-split to heat a house I am designing. I am going to see if I can get away with installing one exterior/one interior wall unit. I know the heat loss is a big part of the equation, but what do folks think of either of these locations for a wall unit (head)? I am hoping to get some flow to the upstairs (assuming the bedroom doors are left open). Just looking for what a pro might suggest. In my rendering, the wall unit locations are modeled in RED. Sorry for the lack of walls drawn in for perspective. One of them is on the rear (or far) wall as you are viewing it.

Thanks in advance from all the knowledgeable pro's here.


  • Larry WeingartenLarry Weingarten Member Posts: 1,948
    Hello, I've only installed a few of these, but things to consider could be:
    1. make the house as airtight and as well insulated as you can. This will help overall, but also will help when recovering from nighttime setback.
    2. Consider installing multiple heads, depending on what areas a unit can reach to heat or cool. I know you didn't mention cooling, but it could become an issue during the life of the home.
    3. I like to use the indoor heads that mount up into the ceiling. These don't look "funny" and give you more placement options.
    4. look into ways of moving air around the house. Home Energy Magazine in their current edition has an article on "Passive Returns", demonstrating many ways of getting air to move how you want it to. :)

    Yours, Larry
  • njtommynjtommy Member Posts: 1,105
    How many bed rooms will you have up stairs?
  • jb9jb9 Member Posts: 104
    There are 3 bedrooms upstairs (and 2 bathrooms back to back). Thanks for asking and sorry for the lack of partitions showing... It's a Timber Frame so I have been focused on exposing those elements as I contemplate the splits. I have a friend who recently built a similar sized house (mine will be 26x32) and he thinks I can get away with a single unit.

    Thanks for the recommendation to tighten up the building envelope too Larry. I definitely have been digging into all the Passivhaus/Continuous Air Barrier/Net Zero stuff. Mostly for the taping/caulking/gasketing techniques and practices.
  • BPHBPH Member Posts: 39
    Are you anticipating all the indoor units being on the first level? And this is a 2 story residence?
  • SWEISWEI Member Posts: 7,356
    I'm also a big fan of four-way ceiling cassettes, especially for open areas. The mini-duct indoor units are usually my go-to for bedroom/bathroom areas. Mount the unit above a closet (even a linen or hall closet) and you can often supply three rooms using ducts that are less than three feet long.

    Tamarack makes inexpensive Return Air Pathways that will make it all flow.
  • bulldoglaxbulldoglax Member Posts: 38
    Just remember that with a tight house and only mini splits you will want some form of fresh air exchange system also, many ceiling casettes have a fresh air inlet that you can probably introduce fresh air into directly. if not you can run a dedicated hrv system if necessary.
  • JackJack Member Posts: 1,045
    I would suggest that you look at Tjernlund's Airshares. They have room to room and floor to floor transfer fans that can make your single unit selection work quite well...depending. You do not say where you are. Are you primarily Heating or cooling. How important is dehumidification?
  • njtommynjtommy Member Posts: 1,105
    Have you looked at the slim duct lines as well from the ductless manufacturers? You could do one of those up stairs with 3 supply lines off of it and a standard ductless head one the back wall of the house and should be fine depending on you heating and cooling requirements.
  • jb9jb9 Member Posts: 104
    Thanks for all the responses so far. It is helpful. The location is in southeastern Idaho in the mountains (lots of snow). High desert. I have a few more questions:

    Are those Return Air Pathways simply installed on bedroom doors, for example?

    Are the ceiling cassettes designed to be above a ceiling or on the ceiling? I plan to have exposed floor joists so I am wondering whether the airflow might be obstructed if a unit were to fit into one of the ceiling bays.

    Also, what is the length limitation between the outdoor unit and the indoor unit? I may try to put the compressor further away from the house if possible.

    Also, let's say you "screw up" and the location you put the compressor isn't working out (gets too much snow to maintain, is too noisy, etc.) Is that a problem a lot of professionals have to deal with? Obviously, I want to try and get it right the first time...

    Are there other brands besides Fujitsu, Mitsubishi and Daikin?

    Hope everyone had a safe and callback free New Years.

  • hvacfreak2hvacfreak2 Member Posts: 498
    I also like the Samsung VRF line ( Samsung / Quietside DVMS ) , I have installed the commercial and single phase versions .

    As far as line length you will have to view each installation manual to determine this , Daikin has mini splits that will go out to 160 feet for example. I seriously doubt that noise will be a problem within any reasonable location.

    4 way cassettes are typically for concealed above ceiling mounting but I'm sure there are exceptions. My personal favorite are the floor convector style units for some of these brands. Also the small ducted units as mentioned.

    Passive transfer openings such as door undercuts can be effective if the structure is reasonably tight.

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

  • jb9jb9 Member Posts: 104
    Thanks for all the responses so far. It is helpful. The location is in southeastern Idaho in the mountains (lots of snow). No need for cooling, the mini-splits will be for heating. I took a look at the Tjernlund Air Shares and they look interesting. How do I approach the movement of air up to the 2nd floor? If I install the unit near the stairs on the 1st floor, can I program and position the louvers to send air up the stairs at a certain time each day? Sorry for the dumb questions... Also, I really wanted to read the article Larry mentioned but I can't get access to the online magazine. Are there places I can read about Passive Returns elsewhere (I assume it is mostly physics)? You guys are really helping me.
  • Jamie HallJamie Hall Member Posts: 13,805
    If you are in southern Idaho, watch out for the minimum temperature these things can operate at. Make absolutely sure that the system you are installing can supply adequate heat at your minimum outdoor temperature! We have had a few folks recently here on the wall who have been disappointed -- to say the least -- when they discovered that their mini-splits quit heating on the colder days...
    Br. Jamie, osb

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • jb9jb9 Member Posts: 104
    Ok. I’m now back after spending 4 hours reading the Fujitsu Halcyon Mini Split 2016 Full Line Brochure… Wow. Lots of information. I may have to start a new thread but I’ll keep this one going for now.

    Here’s what I (believe) I learned. Please correct me if there’s something I don’t understand…

    Fujitsu Nomenclature

    AOU Prefix is the “Outdoor Unit” (I will need at least one of these)

    Cold Design Temperatures means I will skip to the XLTH Series (“H” for High Heat)

    the AOU24RLXFZH jumps out with 24 as 24,000 BTU/hr (25,000 according to their chart)

    Max Line Length Total is 230’ (my house is 26’ x 32’ so no problem)
    Max Delta in height between an outdoor and indoor unit is 49’ (my house is 26’ tall so no problem)

    Outdoor Unit is 32 11/16” Tall and 35 7/16” Wide

    Now I need an indoor unit. The chart says I can have 2/3??? Ok, so I can have one unit downstairs for the open floor plan and one 4 way cassette unit in a closet at the top of the stairs that will feed into each bedroom. Or maybe slim duct that could go ABOVE the closet.

    For open floorplans, I am wondering about a ground unit (ground = low on the wall, right?). I think this might be better than a high wall unit because I could possibly even aim it up the stairs a bit. Does this make sense?

    Getting back to the total capacity of the Outdoor Unit, it seems that you can break down the output as a sum of all the Indoor Unit Evaporator/Fan Coil outputs? Is this more or less how one would “build” a system with more than one “head” or indoor unit? Also, I read that the idea is that all of the upstairs units aren’t really operating at the same time since people aren’t in their bedrooms during the day. So is it possible to transfer the performance to the upstairs indoor unit at night, for example? I assume one would do this by programming (those TV remote control-type devices) the unit on a schedule, right?

    Also, the warranty says DIY is a no-no and they tell you that if you can get an Elite Installer, you could be eligible for the 12 year warranty. Is this effort a worthwhile activity?

    I read about the drip pan heater coil on the XLTH series as well. That is definitely going to be something to pay attention to as one could only imagine the damage an internally impeded fan could cause.

    Sorry for the long message, but I think I now have a better understanding of the product line, how it is organized (very modular-ized and flexible) and how I might site an upstairs unit and a downstairs unit to work in and out of phase during the course of a heating day. I am still trying to figure out where to put the outdoor unit due to concerns about snow, south facing, gable end (East/West) and access so that I can get at the unit with a shovel when it’s really ripping outside.

    Again, thanks for hanging in there with me on this topic. You guys are all so knowledgeable. I am trying!!

  • hvacfreak2hvacfreak2 Member Posts: 498
    Each manufacturer will have their own design protocol that involves software , certain rules for specific models , limitations for specific applications , etc. You definitely want an installation that offers the full extended warranty that comes from a contractor that has full support from the manufacturer.

    Indoor capacity that is higher than the outdoor is called " diversity " . I have seen designs as high as 150 percent , what the outcome was I don't know. For residential or smaller systems I would be careful with this , even if the manufacturer allows it. I think they throw us into testing situations more than we know.

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

  • GWGW Member Posts: 3,790
    Yes 2/3 must mean 2 or 3 units

    Mitsubishi generally lists up to 130%, so you're right you can not expect the math to go backwards, it's just saying what you can do.

    Yes must have a Fujitsu Elite contractor install for 12 year parts warranty. Best of luck trying to find someone to fill out the warranty submission for you if you bypass the traditional contractor, that doesn't make much sense.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • jb9jb9 Member Posts: 104
    Thanks. I hope I can find someone near my site... Also, I definitely won't bank on anything above %100. When one reads the literature, they sort of imply that one isn't using both an upstairs unit and a downstairs unit at the same time. I am going to maintain that assumption as an operational constraint. I would like to avoid purchasing 2 outdoor units, but if it means I get the performance I need on the super cold days, I will consider it. Again, I am going to focus on the reducing the heat load required by the building.

    Another question, what are the exact components that comprise the outdoor unit?

    -centrifugal / sliding vane? compressor?
    -inverter to modulate the flow of electricity to allow the turndown ratio
    -large fan (blowing outward)
    -are there coils in the outdoor unit?

    I am only asking because I am trying to figure out the benefit of having the outdoor unit in the south facing sun (but exposed to west/southwest wind and snow). The sun isn't really going to hit the coils it seems to me because all the components are inside the Unit's housing...

    I'm learning more each day.
  • GWGW Member Posts: 3,790
    Components ---yes that's like asking what's under the hood of a brand new car, do you really need to know? Compressor, condenser coil, controls, sensors, wires, valves, etc etc.

    My opinion is this- if you wish to have heating performance then put the outdoor unit in the sun. If you want ac performance then put it in the shade. Seems like you may want the former.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • njtommynjtommy Member Posts: 1,105
    Take a look at the Floor mount style in door units as well. Heating wise it could be a very nice option with having the supply air coming from the bottom of the unit and going across the floor.
  • jb9jb9 Member Posts: 104
    Thanks njtommy. I was looking at those and I like the fact that some of them let you direct warm air up as well as out from the bottom. I think I am going to post a few more diagrams with what I think might work.
  • jb9jb9 Member Posts: 104
    I have redrawn my proposal based on all the great feedback you guys have shared. I have put in beds to show where the bedrooms are. I also had a talk with an old Refrigeration buddy (from my Zamboni driving days) to ask about location. He said "Gable End." Take a look at the photo and you'll see why. I put a cassette in the landing area because I wasn't sure how to execute a slim duct with air going to 3 rooms... Here's what I think might work. Again, I sincerely appreciate all the help you guys have given me. I just want to have a design that seems like, "yeah, that looks good..."

  • jb9jb9 Member Posts: 104
    And even on the gable end, I know there will be a ton of shovelling to do... It's the massive avalanche / blunt trauma cause of death that I am trying to avoid.

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