GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Fujitsu Slim Duct System

Aun Safe | Posted in Mechanicals on

After seeing them mentioned by Dana Dorsett, I researched the Fujitsu Slim Duct line of HVACs and am talking with a very competent contractor about installing one or two for me.  I’m just curious if anybody here owns one, and if so, how you like it?  Does it dehumidify well?  Maintain a set point with very little temperature fluctuation?  Quiet? Etc.  In general would love to hear real world experiences and whether the system lives up to your expectations.

Would also be curious to hear prices paid.  My contractor gave a ballpark of $8k per unit for the 18k BTU, assuming very little duct work would need to be done.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Aun Safe | | #1

    Btw, I should clarify that by "per unit" I mean per system. I'm thinking about having two installed. (One outdoor unit per indoor unit). I'd probably have one installed first to make sure I'm happy with it and then have the next installed 6-8 months later.

    1. InverterGuy | | #10

      That’s a smart move using two separate systems. I did a three zone ducted off of a single outdoor unit it was a huge mistake we had to take it all out and put three individual units in. Here is what the monitoring look like before we took the old unit out and after we put the new three in.

      1. Aun Safe | | #13

        Wow, am I reading this correctly: With the multi-split you were seeing 5+ degree swings in each room, and with the single-splits the swings are closer to 1 degree or less? Were the huge swings on the multi-split even when you had a constant setpoint?

        Surely there was some problem with the multi-split installation? That temperature control seems so poor that nobody would buy one if that were the norm...?

  2. Expert Member
    Dana Dorsett | | #2

    Elden Lindamood's house in northern Minnesota is heated & cooled with a ducted Fujitsu:

    See John Semmelhack's comment starting in response #4 (and others) regarding setting up the wired remote correctly to sense the temperature at the remote rather than at the incoming air stream.

    USD$8K for a 1.5 tonner is consistent with quotes I've seen in the past couple of years. In competitive bidding with a super-simple duct arrangement you might knock a grand off that in some markets, but not two.

    1. Will R | | #16

      Dana, 2 questions:

      1. Can I fit this slim ducted unit mounted horizontally in my knee wall which runs the length of 2 bedrooms? Theres about 43" from the floor to the rafter with soon to be ccsf (I may ask John the same question).

      2. Recommendations for HVAC contractors who actually know what they are doing in the Boston area? I've gone through multiple contractors through the MA CEC site and haven't been impressed.


  3. Keith Richtman | | #3

    I installed a 1 ton Fujitsu ducted unit a month ago. So far we've been happy with it. It is quiet, though in practice, the indoor unit is noisier than the outdoor unit, perhaps because of the straight sheet metal plenum I used. I did set it up to use the thermistor in the remote control rather than the air handler, but had to adjust the calibration by 5 degrees F for the room temperature to match the setpoint.

  4. John Semmelhack | | #4

    Yes, I have a 3/4 ton unit in my own house and mostly love it. We've designed and tested over 200 of these in the field (mostly 3/4 ton and 1-ton, but the 1.5-ton is quite similar).

    Outdoor unit is very quiet, but in my experience, not as quiet as the Mitsubishi units I've seen. You'll hear some airflow and motor noise if your return is very short and straight.

    Indoor unit is also quiet...the noise you will hear inside has more to do with the duct design/layout than the air handler.

    Temperature fluctuation is good but not perfect...typically within 1F-2F of my setpoint. It often takes some custom configuring of the thermostat to get it respond the way we want.

    Dehumidification is reasonable in cooling mode, quite good in dry mode....but watch out for duct and register condensation in dry mode, since the supply air temperature will be quite cold.

    Super short ductwork is not required...extensive ductwork is feasible with good design and installation. We've served up to 2,800sf with a single unit, while delivering appropriate airflow at a static pressure in the middle of the air handler's range.

    We still haven't found a better system for the kinds of projects we typically work on (new construction apartments, townhouses and large custom houses with good-to-excellent enclosures). I wish there was more competition....

    1. InverterGuy | | #11

      Hey John well said i’m curious what your location is? We do load calculations cfm and air balancing with our systems. We are in a Dry climate out here in California. I noticed you mentioned humidity

  5. Aun Safe | | #5

    Thanks for the replies. Very helpful.

    Keith, any idea why the remote thermostat temperature sensor was off by 5*F? That's kind of alarming.

    John, regarding duct work, is it your experience that static pressure is the most important concern? I believe I've seen that the Slim Duct systems can operate under a max of 0.36". My upstairs system was measured at 0.26" for an oversized 3-ton. The contractor indicated that with a Slim Duct the sp would probably be lower, thereby (hopefully) comfortably falling below the 0.36" max. Manual J shows somewhere in the 14k-16k range for both heating and cooling for my upstairs.

    With those numbers alone, is it reasonable to believe a Fujitsu Slim Duct would be sufficient? Or are there other significant ductwork design issues that could make a Slim Duct a poor choice even though static pressure and capacity seem like a good match?

    Finally, with regards to noise, I assume that the ODU is much quieter than most standard single- or double-stage split systems? Assuming properly designed ductwork, is the air handler louder than most standard split systems? Comparable?

    Thanks again.

    1. kjmass1 | | #7

      I can hear my neighbors conventional ODU unit from about 50' away. I can stand next to my Fujitsu unit and it really is close to silent. Even at full speed it might be quieter.

      I'd recommend installing the wired controller if you want it +/- 1 degree on the floor. I had to mess with the offsets as well but once you get it locked in they work pretty well. The split operates in 2 degree increments, and you can have a couple degree spread from floor to ceiling.

      I can only comment on a wall mounted Fujitsu split, but when it is just humming along at low speed, it's quieter than my fridge.

    2. InverterGuy | | #9

      If you were installing the low static model you should put in new ductwork no matter what. The ductwork for each room needs to be size for the exact CFM needed for it to be perfect. Air balancing should be done as well. If you are using your existing ductwork I would recommend going to the medium static 18,000 BTU air handler it will handle up to .65 static.Just because the existing system has low static pressure does not mean you will get the correct Airflow throw velocity out of the existing duct system. For an 18,000 BTU system you should be paying around $12,000 with all new engineer duct system And airflow balancing. For best results do it right.

  6. John Semmelhack | | #6

    Correct - if you're replacing a 3-ton (~1200cfm) air handler with the 1.5-ton Fujitsu unit (~600cfm), and if the total external static pressure on the 3-ton system is 0.26in.w.c., then the Fujitsu system should have no problem moving the right amount of air...just needs to be tested and installer speed setting adjusted to make sure the total system airflow is on target.

    The only other distribution issue to be aware of is the registers. If you have registers that were sized for larger airflows that will now receive about 50% of the airflow, then you'll significantly less throw, and possible poor mixing within these rooms.

    The ODU is SIGNIFICANTLY quieter than standard outdoor units. Air handler is generally quieter than a typical PSC motor air handler.

  7. InverterGuy | | #8

    I am actually a building performance guy out here in California. Our company has installed over 75 of these in the last year and a half. All engineered with load calculations room by room air flows air balancing and careful attention to detail on the duct work. Averaging about 1100 square-foot per ton with some envelope measures, the systems perform amazingly well. They keep the temperature within a degree most are nearly silent and they have the reserve capacity they need to get the job done fast when needed. Were in a fairly dry climate and it’s mild here but it does cover 100 and below 32 occasionally. I have done a couple of these 18,000 BTUs in 1900 square-foot homes that work very well. If your contractor is offering to install a standard 18 RLFCD on your Existing duct work it is likely not going to work well. You will need the medium static 18RGLX.

    1. Jon R | | #12

      Is it true that the fan has a very limited range compared to the compressor, making it a poor fit for humid climates? Specifically, they have a poor sensible heat ratio/dehumidification at anything much less than 100% compressor output?

      Non ducted units have a greater fan range and even they can be lousy at latent removal at less than 1/2 load. See Table 7:

    2. Mangesh Ghiware | | #14

      Hi InverterGuy, I'm located in SF Bay Area and looking to install a Fujitsu or Mitsubishi system in a 1600sf house with new duct work. Any recommendations on good installers in the area? I can share my contact info if that's easier.

      1. Expert Member
        Dana Dorsett | | #15

        >"I'm located in SF Bay Area and looking to install a Fujitsu or Mitsubishi system in a 1600sf house with new duct work. Any recommendations on good installers in the area?"

        Larry Waters of A1-Guaranteed Heating & Air Inc. out of Vallejo designed and implemented the well done retrofit in Berkeley on the main picture here:

        That's the picture of the system before building out the soffits around the ducts, and the partition walls of this tiny <10 square foot "utility closet".

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |