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Fujitsu minisplit heat figures

mcmodern | Posted in Mechanicals on


Hopefully the heat output tables for the ceiling cassette and wall mount fujitsu units are attached!

Am I understanding this correctly??

At my 99% outside design temp of 5f, and as I read this,  the heat output of the 9kbtu ceiling cassette [rlff] is the same as the 9kbtu wall mount[rls3]? but the COP is much higher [capacity/input in kw]

Indeed it seems that at the lower range of temps, -5f to 14f, the ceiling cassette puts out the same heat with a better COP.

The wall mount output and cop improves as the outside temps increase, but the house  heat load decreases…



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  1. Expert Member
    Dana Dorsett | | #1

    You are understanding it mostly-correctly. It's a bit hard to say what the input power is at your actual load. The COPs and capacities given are at max-speed, which isn't the speed at which you're running it.

    The COP curves at part load aren't simple straight lines from max-speed capacities & input power- the coil shape and aerodynamics of the vanes etc all have an effect, and can't be inferred from the capacity tables. You're better off looking at the HSPF numbers, which are calculated from the efficiency at the "nominal" or "rated" modulation levels (= not maximum speed) at +17F and +47F.

    The 9RLS3 tests at an HSPF of 14.2 when married to the AOU9RLS3 compressor unit:


    the AUU9RLF tests an an HSPF of 13.0, when married to the AOU9RLFC compressor:

    They are slightly different compressor units, and operating at part load for the HSPF tests.
    It's a bit like comparing apples & pears, but it's way better than trying to compare them based on their COP at max-speed across temperature, since they're never actually operated that way.

  2. mcmodern | | #2

    Hello Dana, thanks for the reply / info.

    Sorry to ask what may be dumb questions! :-)

    I prefer the ceiling cassette, because in this location, it is much less obtrusive than the wall mount. and 4 direction air flow is more suitable.

    at 5 to -14f, aren't you likely to need to be running at/near max output, because you are at the max heat load? [if the ashp is sized correctly]

    Because of the cassette's lower HSPF, I was expecting the cassette to put out either less heat, and thus not be able to meet the 5f design load, or have a worse COP vs the wall mount [indeed the floor mount does not put out as much heat and has a worse cop at 5f]

    Don't these figures show that the cassette puts out the same max heat as the wall mount [and maybe more efficiently]? @ 5 t0 -14f

    is the wall mount higher HSPF as a result of better performance in the 17-47f range?

    for others looking at very cold weather installation; the wall mount comes with a base pan heater. I don't see if the cassette can/ does or whether it can be added. and the wall mount comes with wifi . the ceiling cassette has a built in condensate pump.

    the fujitsu cassette documentation is all over the place, with info from 2010, 2013 and 2018 all given as current. for example, it seems the significant, "high insulation" 95 setting only appears, buried in one of the 2018 documents.

    primarily, my concern was that the ceiling cassette would not be able to meet demand/max heat load vs the wall mount.

    Thanks again and sorry if I'm barking up the wrong tree!


    1. Expert Member
      Dana Dorsett | | #3

      >"at 5 to -14f, aren't you likely to need to be running at/near max output, because you are at the max heat load? [if the ashp is sized correctly]"

      >"Don't these figures show that the cassette puts out the same max heat as the wall mount [and maybe more efficiently]? @ 5 t0 -14f"

      Since the 99% outside design load is only exceeded 1% of the time ( 87 hours per year in an average year) you almost don't even care what the COP is at those temperatures. The COP at the wintertime AVERAGE temperature & modulation level is a much better indicator of overall energy use, not the 99th percentile extremes.

      According to NEEP data at +17F the COP of the 9RLS3H @ is

      --- 2.12 at it's max modulated output of 16,000 BTU/hr

      --- 3.36 at it's AHRI "rated" output modulation level of 7000, BTU/hr

      --- 1.86 at it's minimum modulated output of 2,286 BTU/hr

      For the AUU9RLF the COPs are

      --- 2.66 at it's max output of 16,100 BTU/hr

      --- 2.88 at it's AHRI rated output of 9,400 BTU/hr

      --- 5.65 at it's minimum output of 2,744 BTU/hr

      >"primarily, my concern was that the ceiling cassette would not be able to meet demand/max heat load vs the wall mount."

      So, what's your 99% outside design temperature, and load at that temperature?

      What is your heat,load at +17F?

      What is you average outdoor temperature & average load for the coldest 10-12 weeks of the heating season?

      The ceiling units are pretty efficient- they probably sell more of those in Japan than wall coils (they're everywhere in restaurants and commercial/retail space.) The down side to the ceiling cassettes for the north American residential market is their physical size- they don't fit between 16" on center joist spacings, and need the framing designed to accommodate them. They'll just make it between 24" o.c. framing in one orientation, but not turned 90 degrees. Height wise at 10-5/16" from the ceiling paint to the top of the cassette it doesn't fit 2 x 10 joist framing unless it's open above.

      Several months ago I recommended a AUU12RLF to a guy in NJ who already had the appropriate framing & hole in his ceiling that had previously accommodated a whole-house fan. He had been thinking of it only for air conditioning, but I pointed out that it would also be cheaper heat than he was getting out of his oil-burner.

      1. joshdurston | | #4

        That's weird that wall mount has such a low COP at min modulation versus the ceiling cassette.

  3. mcmodern | | #5

    thanks all for the replies

    yes, all the figures are a bit weird :-)

    I've got that NEEP spreadsheet but it doesnt like google docs and is clumsy to view, I'll convert it to sheets and take another look.

    Dana, did you recommend the 12 over the 9 for cooling loads [as he was replacing a whole house fan] ?

    the 99% is 5f

    the heat load/manual J is a very best "guess" as the unusual layout of the mid-century modern house, which is split level, part cathedral ceiling and almost entirely open plan, does not model well. [but looks great! :-)] a deep energy retrofit should make it a supertight, "very good" house

    heat is the dominant factor for this head location, which is why I'm looking at the options for wall, floor, ceiling.

    It seems the heat output of the larger ceiling units [12 and 15] is not significantly higher, and with a lower COP] and it seems the fujitsu cassettes are "better" than the mitsubishis for heat.

    Thanks again

    1. joshdurston | | #6

      It seems like Fujitsu is the top of the heap when it comes to ASHP heat. I love that they don't seem to have a low limit unlike everyone else . I think best effort is better than giving up in deep cold.

    2. Expert Member
      Dana Dorsett | | #7

      >"Dana, did you recommend the 12 over the 9 for cooling loads [as he was replacing a whole house fan] "

      IIRC it was a bit of both- to cover more of the heating load for that end of the house, (which included a living room, entry hall bathroom, and a couple of bedrooms) and for cooling. For cooling-only the AUU9 was a bit marginal but probably would have been enough, but the up-charge to the 1-ton was pretty small, and was a better compromise overall. Even though his whole house heat load came in considerably higher than the capacity of AUU12 it was clear from his floor plan layout and the location of the unit that only part of the house was going to be heated/cooled by one ceiling cassette.

      On the other end of the house he had a large (oversized, really) 1980s vintage through-wall AC unit in the kitchen in a location that that could reasonably serve the dining room & pantry as well. I suggested he might consider a 3/4 ton minisplit or a 1-ton PTHP to replace that when that beast was ready to retire.

      It was remarkable to me just how much more heating capacity the Fujitsu units had at the relevant heating temperature than the 1-ton Daikin & Mitsubishi ceiling cassettes he was considering.

      If Mitsubishi had a 1-ton H2i single zone ceiling cassette minisplit it could probably be comparable to the Fujitsu for capacity @ +5F, but they don't.

  4. mcmodern | | #8

    thanks all again for the replies/info

    any thoughts/knowledge on base pan heaters for the Fujitsu cassette outdoor unit?


  5. Expert Member
    Dana Dorsett | | #9

    I don't know for sure, but I don't believe there is a heater pan option for the
    AOU9RLFC compressor unit. The schematics don't show any indication of a pan heater control:

    People run them in very cold climates, but it's probably a good ideal to check for ice build up every few days during extended weather that stays cooler than 20F.

  6. mcmodern | | #10

    thanks Dana

    do you know if heat tape under the pan would work?

    also, any thoughts/experience on insulating the lineset with more than the 3/8 foam that seems to be standard?

    it seems to me that there might be a benefit, at very low cost, to much thicker insulation on the lineset.


  7. Expert Member
    Dana Dorsett | | #11

    On small diameter pipe the benefits of thicker insulation decrease pretty rapidly, because the exterior surface area increases rapidly with thickness. Don't sweat that one.

    A guy posting here under the handle Hobbit has a 2 ton Daikin with no pan heater and has worked on some solutions for his defrost ice build up, but I don't recall the particulars. He used to have a blog page full of details of his deep energy retrofit and heating system, and some of those details were discussed here a handful of years ago. Try different ways of searching. I came up with this pretty quickly.

    He's still posting here occasionally.

  8. mcmodern | | #12

    Thanks Dana

    for folks researching mini splits, I found "Garage Journal" has a lot of recent detailed user experiences, detailed installation info etc, with a lot of brands. They are becoming very popular for workshops/garages.

    I searched in the forums for "mini split"

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