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Community and Q&A

Ductless / Ducted Combination Minisplit System

drewintoledo | Posted in Energy Efficiency and Durability on
I don’t completely understand the information specifications provided with HVAC equipment.  Can anyone provide feedback on whether or not these units are a good fit for my application?
Windows are triple pane, attic R60, walls no less than R30, 9′ ceilings about 1900 square foot ranch.
Manual J attached.  Location NW Ohio.
Two units being recommended are ducted Daikin FTX12NMVJU for the bedrooms and ductless Daikin FDMQ18RVJU for the living area.
Do they modulate low like the other units (Fujitsu, Mitsubishi, etc)?  One note; I believe both will connect to one outdoor compressor unit.
I’ve marked yellow where the units will install.  The ducted unit will be in the basement and will feed the bedrooms and baths.  The ductless unit will install in the living area.

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  1. utah_matt | | #1

    I crossed checked my design with this website.!/product_list/

    The advanced search proved most helpful.

    My calculations showed the loss per floor so we sized each Daikin unit based on the heat load for the specific floor.

    Generally speaking the units you had sized line up with mine except we specified the Aoura version which has much better cold weather output.

  2. Expert Member
    Dana Dorsett | | #2

    >"Two units being recommended are ducted Daikin FTX12NMVJU for the bedrooms and ductless Daikin FDMQ18RVJU for the living area."

    There are some inconsistencies here. The FTX12NMVJU is a high-wall coil type, not ducted. The FDMQ18RVJU is a compact duct cassette, compatible with more than one version of the compressor.

    The low temp <+15F performance this serise is fairly pathetic compared to the better-versions, and would underperform significantly during a Polar Vortex disturbance cold snap. The RX_L_ version of the -12NMVJU compressor has significantly better low-temp capacity & efficiency than the RX( non-L) version:!/product/30704/7/25000///0 <<< the cold climate version

    vs.!/product/25254/7/25000///0 <<<same compressor as the one in your posted submittal, different high wall coil, but pretty similar

    Same story with the 1.5 ton ducted unit- it performs way better with the RXL version of the compressor...!/product/33598/7/25000///0

    ... than the RX (no-L) version:!/product/33588/7/25000///0

    Given that capacity the RXL version of the 1.5 tonner exceeds your design loads for both cooling & heating is there a reason you don't just make it a single zone using the ducted 1.5 ton RXL rather than two lower performance versions, each sub-optimally oversized for their zone loads?

    Regarding the Manual-J, why the indoor design temp of 72F for cooling? AHRI efficiency & capacity is tested at 80F indoors, most people are just fine at 75-76F as long as the humidity is under control.

    If you are still planning to use two, with the ducted mini-split serving the bedroom zones, the 3/4 ton RX09RMVJU coupled with the FDMQ09RVJU cassette most likely covers the bedroom design load with margin, and would have a better modulation range.!/product/57000/7/25000///0

    If the room by room load numbers indicate that's not enough, bumping it to the 1 -ton RXL version would surely get you there:!/product/56998/7/25000///0

    (For some reason Daikin doesn't match their 3/4 ton ducted cassettes to the cold-temp performance RXL09RMVJU compressor, only the RX.)

    1. jameshowison | | #25

      Anyone know why Manual J allows changing these temperatures? Where they are required by AHJ/code is one allowed to change the inside temps?

  3. paul_wiedefeld | | #3

    Those aren't a good fit. Your manual J shows 24k btu heat loss but these two don't get there at 9 degrees. Is there a reason you're going with a ductless unit for the living room? You could just run ductwork for the full house which lets you incorporate backup resistance heat and fit the load better

  4. drewintoledo | | #4

    No. No reason at all. I don't have a problem admitting I am pretty clueless here and that's why I'm reaching out.
    I'm open to all makes/models if you guys would like to tell me which unit would be best in this scenario. I would rather have a unit that can pull weather out of negative degree weather as we do see that from time to time.

    1. paul_wiedefeld | | #6

      Most output some heat below 0 while the cold climate options output significant heat under 0. As you have a small heat load, matching the cooling well and adding just enough electric resistance backup for the coldest hours might turn out to be optimal. Daikin makes plenty of centrally ducted options in the 18,000-24,000 btu range, as does Mitsubishi, Fujitsu, etc.

  5. walta100 | | #5

    “I believe both will connect to one outdoor compressor unit.”

    Understand when you have multiple heads the outdoor unit can be slowed to about 33% of its max 30,000 so when the load falls below 9,900 BTUs the unit will begin cycling on and off lowering its efficacy. Most single head unis will slow to 10% of its max of 12,000 so the load must fall below 1,200 BTUs the unit before it begins cycling on and off if you turned off the larger unit 9X diference.

    Yes, separate systems will likely cost more to buy but sooner or later every system fails when it does the separate systems has the advantage that you will still have some heat while the multi head system will have no output.

    Trust your gut and hire the installer you feel best about.


  6. drewintoledo | | #7

    I've had my Manual J tweaked a bit for 0° weather and 76° indoor temps. Attached are results.

    Also my installer retuned message to me and stated, "I had planned to use the Aurora system RXL12QMVJU9 With high wall unit and RXL18UMVJUA with the ducted system." The RXL is the system Dana mentions, but I believe it's also oversized?

    Then my installer finished with, "I would be more than happy to give you proposal for any system that you would like as I would want to install what you are comfortable with what you want in your home. The unit cost may change slightly but the concealed ducted unit in the aurora model is only available in the 12k, 18k & 24k btu."
    Having said that, would you gurus recommend something like a Mitsubishi or Fujitsu cold weather climate system? Dana also mentions a single ducted system. But.. which system is best for my design? What would you choose? Please continue to guide me along my journey. I'd rather get it right the first time.

    1. Expert Member

      At 76 degrees indoors I'd be running around panting. Do you keep your thermostat on 76 now?

      1. Expert Member
        Akos | | #16

        I get into trouble if the house is colder than 25C (77F).

        More than temperature, what I find makes the biggest difference is getting humidity down. The 25C with around 35% RH is actually quite pleasant, above 55% RH starts to be uncomfortable.

        1. drewintoledo | | #17

          kbentley57, AKOS said it. If I keep my humidity down, the temps can stay slightly higher. Right now, I'm very comfortable and my ACURITE 00613 Digital hygrometer & Thermometer shows 75° and 38% humidity. Add a fan it's it's almost chilly. Sidenote: I've recently built a barn with a loft area. In this loft I installed a DIY minisplit system. I've had no prior experience with minisplits and was pleased to see this model can act as a dehumidifier. If the humidity is kept down, it's very pleasing. I find myself running the dehumidifier quite often.

          1. Expert Member
            KYLE WINSTON BENTLEY | | #20

            I have a Withings Airthing that I've been monitoring with for the past year. The only time my house can drop below 50% is in the {Jan, March} months where the outdoor RH drops below 40%. Such is life I guess.

        2. jameshowison | | #26

          I think a key point here is that everyone in the house is more likely to be comfortable at the same temperature when humidity is under control.

          ie if humidity is high I want the air temp like 5° lower than my wife, if humidity is low then we are happy at the same temp.

          So humidity control means fewer thermostat fights. That should be the marketing pitch for whole house dehus!

  7. Expert Member
    Dana Dorsett | | #8

    The room by room, zone by zone load numbers from the Manual-J are important for figuring out whether this can work reasonably with a single-compressor multi- zone outdoor unit, and to properly size the cassettes/heads. The submittal sheets posted are for single zone systems, with a separate compressor for each zone.

    As a general rule it's easier to hit both efficiency & comfort goals with multiple dedicated single zone mini-splits than a multi-zone compressor. For a higher-performance houses the room to room temperature differences usually aren't very big even if operating it as a single zone, and using a modulating single-zone ducted system may be more efficient & comfortable than a 2-zone multi (especially if the heads/cassettes are oversized).

    The ~28K heat load @ 0F outside/70F inside seems high for a 1900' house with R30 walls and triple pane windows, but not crazy high if there is a lot of window area. That's a load/floor area ratio of about 15 BTU/hr per foot, which about where most 2x6/R19 type houses with U0.32 double panes would come in. Even my 99 year old 2x4/R14 house with wood sash double-panes + clear storms (no l0w-E) has a load/floor ratio of less than 17 BTU/hr @ 0F outdoors, 70F indoors. My suspicion it that your heat load (but not necessarily your cooling load) is way overstated here, and the LAST thing you want to do is oversize the equipment, since modulation ranges are not infinite, and short cycling takes a toll on comfort & efficiency.

    Without the full Manual-J it's hard to look for where any errors might have crept in. HVAC contractors have a natural instinct to be overly conservative on their inputs to the Manual-J, and since R30 walls are not code-standard wall construction it's unlikely that they got the wall losses correct. Since I don't use Wrightsoft I don't really know if your wall construction is selectable from a pull-down menu. Many contractor Manual-J's use code-minimums for everything, even when the house is clearly WAY better than code.

    You may want to run your own Manual-J using BetterBuiltNW's free tools.

    Since the walls are not standard construction you'd have to calculate and edit-in custom U-factor for the walls, and use the manufacturers' U-factors for the windows. It's a fairly easy to use tool (even HVAC contractors can get it right! :-) ), purpose made for sizing heat pumps. The development of that tool was paid for by a consortium of utility companies in the Pacific Northwest in response to myriad comfort & efficiency complaints by customers participating in their heat pump promotion programs, all stemming from gross oversizing by the HVAC contractors. They intentionally use fairly aggressive default U-factors & air leakage, etc for standard construction, and unlike Wrightsoft & other Manual-J compliant software there isn't an automatic 15-20% fudge-factor built in. Sizing the equipment using the BetterBuiltNW tool makes it far less likely to oversize by suboptimally large margin.

  8. drewintoledo | | #9

    Thank you Dana, here are a few more pages from the results. I am hopeful you can further comment on a recommendation.

    1. Expert Member
      Akos | | #10

      The software is not calculating wall assembly values properly. Looks like your R30 walls end up as an R21 assembly (1/U0.048). I would tweak insulation values until the assembly U value calculated matches your actual assembly. This is a pretty good calculator for these things:

      There is also about 1/2 ton of infiltration losses. I would change the infiltration values to what you tested at or what you expect to hit. Based on your description of the reno, I doubt your place is "semi-tight".

      I'm with Dana on the heating equipment. If you are already mounting a ducted unit in the basement for the bedrooms, you have done 90% of the work. To use the same unit to heat the whole house would mean adding on about 3-4 extra ducts plus registers, the cost of that is WAY less than an extra wall mount even if you have to go a 1/2 ton up on size. You also get much better heat distribution and less maintenance.

      About the only thing you loose is a bit of zoning which might be moot anyways in a high efficiency single story build where temperature will be pretty even in the whole house no matter what you do.

      Even if you do go with a two zone setup, one to one is the way to go. Overall equipment cost is about the same, install cost is a bit more but you get redundancy, higher efficiency and much better modulation range. This also gives you the option to run one unit in heat and one in dry mode in case you have major humidity issues in the shoulder season. Saves the cost of a dehumidifier and cheaper to run.

      1. drewintoledo | | #11

        Thanks buddy. When you said, "Based on your description of the reno, I doubt your place is "semi-tight"." By reno do you mean rennovation? This is a new build. I'm paying extra attention to sealing, taping, etc. and plan to finally hit the house with the aerobarrier system when I'm ready.
        Thanks for the Wall R-value calculator! That's pretty neat!
        I've sent a link to this thread to my Manual J dude so I'm hoping he will browse and make adjustments. I also noted on one page that the latitude which is listed as 38° is incorrect (I'm 41°) but I'm unsure if that makes too much difference. I'm not too worried about zoning, but I do like redundancy.
        Can you tell me what you mean by one-to-one? Do you mean two ducted systems to create two zones?

        1. Expert Member
          Akos | | #14

          One to one means each indoor unit on its own outdoor unit. These generally are more efficient than a multi split (one outdoor unit for many indoor units) and have much better modulation range.

          In your case, I think by the time you dial in your Man J, you'll most likely find that the heat loss will be above the smallest pair of ducted units. Unless there is a very good reason for the 2nd zone, I would stick to a single unit.

          You can spec a mid static unit such as a Fujitsu GLXD/ Mitsubishi PAED / Daikin FDMQ which deliver 0.6" WG pressure which is not far off from a standard air handler at 0.8". These can easily supply more complex runs of ducting that you might need to reach the whole house.

          Any of the above with the right sized cold climate hyper heat outdoor unit should work great in your climate.

    2. Expert Member
      Dana Dorsett | | #12

      Per the Manual-J the calculated design heating load of the two bedrooms combined only adds up to ~3600 BTU/hr, which would make even a 1-ton compact duct cassette obscenely oversized, and a 1.5 tonner GROTESQUELY oversized, and would yield the opposite of "comfortable & efficient". At +5F (colder than your design temp) the lowest the RXL18UMVJUA can throttle back to is 4700BTU/hr. When you add in the heat generated by 3 sleeping humans it means it wouldn't modulate much with load until it's well below zero F outside, and would be cycling like crazy under average conditions

      Using some other vendors' cold climate ducted 3/4 tonner might work out OK for that zone, but since Daikin doesn't make a single zone ducted 3/4 ton unit they don't seem to have anything that would be a great fit. Using a 2-zone system rather than separate single zone systems would be even worse, all of which points to running it all as one well balanced ducted system, no zoning.

      For a single unit running heating/cooling the whole house the 1.5 ton compact-ducted Daikin SkyAir FBQ18PVJU/RZQ18TAVJU might be about right:!/product/25272/7/25000///0

      It's tested HSPF is somewhat lower, but it's ~28,000 BTU/hr capacity @ +5F is higher than the ~22K delivered by the RXL18UMVJUA, which might come up short for heating the whole house (still TBD.) The as-used HSPF of a miserably oversized system driving the 3600 BTU/hr design load of the bedroom zone would never be able to meet it's efficiency spec due to cycling losses, but it would likely hit near it's tested numbers if heating the whole house. If the load at 9F really is substantially more than 22K, going with the 1.5 ton SkyAir wouldn't be terrible.

      Akos has it right that the U-factor for the wall seems a bit off. The construction description is 24" on center 2x6 studs with R21 cavity insulation plus continuous R12 exterior foam board on the exterior. Is that in fact what you have? Even though the window descriptions in the Manual-J are double-pane, the U-factors most the windows listed are U0.17, which is typical for triple panes (and effectively impossible for double-panes.) I'm hoping those were manually entered based on the manufacturers' specs. Akos is also right that with your meticulous air sealing the actual air tightness will be much better than the tool's simple default for "Semi-tight", thus overstating the infiltration losses.

      The shift to using conditions at the Reagan Airport in Washington DC for the design temps & humidity seems odd, if you're in NW OH. They somehow got the location correct on attachment in your original post.

  9. drewintoledo | | #13

    Thanks again Dana and others. It's starting to come together for me. Yes it is true that I have started installing R12 3" Rockwool on the exterior minus the common garage wall which I might spray with closed cell but most likely will leave at R19 fiberglass batts. Original thought was dense pack cellulose in the walls, but it seems that R19 fiberglass batts might be easier and lower cost for me to install. Sidenote--I was suprised that the vinyl siding added +R1 on the wall calculator even with a rainscreen. Basement has 2" EPS R8.8 under the floor and 3" around the exterior which I believe is R13. I will be adding another 2" R8.8 around the interior basement walls and I build.
    The windows are triple pane, 70mm 180CL glazing from Ventana manufactured in Pittsburgh but are rebranded as Logic and sold out of Maine. I might have that number (.17) incorrect as it appears the u-value is .18 I am grabbing the info from -->
    I'm also going to invite my HVAC installer to this thread to enable him to absorb the wealth of information you and others on this have provided.
    Thank you all for helping guide me to the unit(s) that will function best in my application.
    I've already had another contractor tell me, "Attached is the system I would recommend. As I went through the print, I don’t feel like your house would be the best application for a mini-split system. Please feel free to contact me anytime with any questions you might have". I know better and that's why I came here for guidance.
    Is it possible that the air infiltration numbers being used have been entered because of the Broan 170 ERV system I plan to install? I'm waiting for manual J guy (Jerry) to peruse this thread and respond either here or via e-mail.
    For those interested, I have been documenting my build as I progress. I'm not the best narrator but I'm only doing this for myself so I can look back at the videos years later to reference and enjoy. I'll be posting my HVAC install at somepoint and it's all thanks to you all. Feel free to subscribe and follow along if you wish.

  10. drewintoledo | | #18

    I've found a Mitsubishi certified dealer. I've provided him the manual J and he came back with the following equipment which seems overkill.
    (1) Model: MUZ-FS18NA-U1 18,000 BTU Outdoor Unit (Living Room)
    (1) Model: MSZ-FH18NA 18,000 BTU Indoor Unit (Livingroom)
    (1) Model: SUZ-KA18NAHZ.TH 18,000 BTU Indoor Unit (Master, Baths & Guest)
    (1) Model: SEZ-KD18NA4R1TH 18,000 BTU Ducted Indoor Unit (Master, Baths & Guest)
    I don't believe that I need two 18k units.
    Can anyone please respond with the proper Mitsubishi equipment model numbers that will better suite my build?

    1. Expert Member
      Dana Dorsett | | #19

      (sigh...) These guys are absolute idiots (will they ever learn?)

      You don't even need ONE 18K unit unless the Manual J is severely understating your loads (not likely.)

      >"(1) Model: MUZ-FS18NA-U1 18,000 BTU Outdoor Unit (Living Room)
      (1) Model: MSZ-FH18NA 18,000 BTU Indoor Unit (Livingroom)"

      Per the Man-J the total heat load for the living room is 3675BTU/hr @ 0F, the cooling load is 3996 BTU/hr @ 92F.

      Even at +5F the LOWEST that combination can modulate down to is 2050 BTU/hr and at +17F the lowest it can go is 2950 BTU/hr, which is above the actual heat load (~2700 BTU/hr @ +17F). The thing would be doing nothing but cycling on/off any time it's above 17F, and cycling a LOT when it's above freezing.!/product/34602/7/25000///0

      The ENTIRE house load is 23K (even includes the basement) which is just barely above what that beast can deliver @ 0F!

      The MUZ/MSZ FH09NA can modulate all the way down to 1600 BTU/hr @ +47F, the heat load would be about 1000 BTU/hr @ +47F, so even when it's in the 40s F it will have a fairly high duty cycle, and it would modulate most of the season. Even at 0F it has more than twice the capacity to cover the 3675BTU/hr heat load, and ~3x the capacity of your cooling load @ 92F. You could save (at most) a couple hundred and go with the FH06 and STILL be covered 2x for the living room zones, but it's low modulation range & efficiency is the same as the FH09 (which may be more available):!/product/34597/7/25000///0

      If the living room unit is also going to be heating the kitchen & stairwell etc, go with the FH09.

      Similarly the SEZ-KD09NA/KA09NAHZ combination delivers more than 10K max @ 0F at max, way more than actually needed. I'm not sure what the min-modulation @ +17F or +47F is (somehow my NEEP login failed when I tried to pull the sheet on that), per the AHRI submittal sheet:

      Add up the total zone loads, multiply each by 1.2. If that's above the max capacity of the equipment @ +5F you might bump up to a 1-tonner (FS12 or KA12) but a 1.5 tonner for either zone is only going to cost more up front and deliver LESS comfort, at lower efficiency.

      1. Expert Member
        KYLE WINSTON BENTLEY | | #21


        I just want to say that I appreciate your posts. I learn a lot from every one I've read.

        1. drewintoledo | | #24


  11. kyle_r | | #22

    Drew, have you considered serving the whole house with one ducted unit?

    1. drewintoledo | | #23

      I have, but I like the idea of being able to shut down 1/2 of my system if needed. Especially since the living/dining/kitchen area is within an open floorplan that contains a good deal of south-facing high solar heat gain coefficient windows. If I overheat I can simply turn off the ducted system completely. I also like the idea of having redundancy.

      1. Expert Member
        Akos | | #27

        Looking at your floor plan, bedrooms take up about 1/3 of your exterior wall area, take out basement and ventillation heat loss, you are probably looking at a heat loss of ~5000 for both beds and baths which is very small even for the smallest 9k slim ducted unit.

        You might want to go for a non hyper heat unit for the bedrooms something like this from Mitsubishi:!/product/29057/7/25000///0

        No matter which one you choose, once it gets warmer, the heat loss will be above the min output and can cause some cyling.

        My suggestion would instead be to stick to a hyper heat unit (PEAD-A09AA7 SUZ-KA09NAHZ) but add some extra load to it and duct part of the living space and basement as well. Having supply registers under larger windows can make the house feel much warmer and might be worth it to add these in to balance the system. This also means you can go with a much smaller wall mount for the living space like this for the rest of heat loss.

        A 9k wall mount can easily cover the rest:!/product/34426/7/25000///0

        As others have suggested, your best bet is to go with a single high static air handler in the basement to supply the whole house.

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