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Installing Fujitusu 15RLS3H split system – What wired remote is best for achieving accurate set points?

rocket190 | Posted in Mechanicals on

Fujitsu offers two wired thermostats for the 15RLS3H package. It seems like others are having problems with getting accurate temperature control using only the thermostat in the indoor unit, so I was looking to get the proper wired thermostat right away.

The two options are UTY-RVNUM and UTY-RNNUM.

The UTY-RVNUM thermostat is backlit and has a nicer looking interface, but it’s over $300 for just the remote.

The UTY-RNNUM thermostat is about half of that price, but there is a note saying 15RLS and all HFI Wall Mount type Multi-Zone systems require accessory interface kit # UTY-XCBXZ1 in order to connect the UTY-RNNUM controller.

From a functionality perspective, will they both do the same thing?

My second unrelated question is can someone help me understand the air velocity distribution chart I’ve attached? in an open floor plan, 20′ x 38′, with the unit mounted in the center of the room, “throwing” heat the long way, would you anticipate any problems? I’ve performed the heat loss calcs and the 15RLS3H will be more than sufficient in my 6a climate.

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  1. STEPHEN SHEEHY | | #1

    Rick: In a roughly similar space, our 12RLS3H works fine. It's in a corner. I set the vanes to blow a bit to the side, toward the center of the room. We're also in zone 6.

    I've read various posts about the remote temperature setting not working. Mine works fine without a separate thermostat. The unit is about 9' above the floor, 3' from the corner and 18-20" below a sloped ceiling. I think placement matters, especially distance from the ceiling. If you must place it close to the ceiling, you might need the thermostat.

  2. rocket190 | | #2

    Stephen that's reassuring to know. Have you had to use supplemental heat to maintain a comfortable temperature, or did your unit keep up on cold days? My unit will be positioned slightly off center, so I will probably adjust the louvers so slightly angle the heat through. My only door is to the bathroom, so I will probably add a small 1500 watt space heater with thermostat to adjust for any shortcomings. My ceiling height is 8' 7", so I have the room to move the unit down if needed.

    In a nutshell, my walls will average R-35, my ceiling R-60, and my floors R-52, and windows R5.2. I have been air sealing maniacally, but I will say that air sealing a bonus room is every bit as difficult as advertised. I am planning on using a thermal imaging camera to locate any weak spots.

  3. STEPHEN SHEEHY | | #3

    Rick: I haven't needed any supplemental heat at all, which is a lucky thing, because I don't have any. Our winter in Maine has been mild, but at-8 F, the minisplit kept up without a problem. The remote is set to 68, and we're usually within a degree of that, whatever the outdoor temperature.

  4. rocket190 | | #4

    Awesome news. Thanks.

  5. bunney | | #5

    Rick: I am in zone 6, R 29 walls, R56+ ceilings, R8+ windows with R3 to R4 blinds (Symphony with sidetracks). Under insulated concrete floor with only 4" foam. 2" exterior foam slab on grade.

    We have Fujitsu Halcyon rated to -15. One head is in the vaulted great room (15' x 28') of our 1,100 sq ft passive solar home. We use remote thermostats, which seem to work fine. The mini-splits are mounted about 8 ft above the floor. The great room unit faces the narrow width of the room, which I assumes contributes to the room's "cold" spots referenced below. The 2nd head is in our, bedroom where it has kept us very comfortable.

    We supplemented the heat pump with wood stove heat this winter during a couple weeks when some nights reached below -15. I knew at those temps that the heat pump wouldn't be operating efficiently. We also have hydronic / electric resistant baseboard heaters as backup that we have seldom used.

    I am disappointed in Fujitsu. The unit briefly blows relatively cool air whenever it is resumes heat mode after defrost, which is frequent during coldest parts of winter. The units are, for some unknown reason, still periodically blowing cool air this spring.

    Whereas, my understanding is that the blowers of the Mitsubishi units do not turn on after defrost until the unit has heat to dispense

    Meanwhile, the great room/kitchen this winter was commonly at 78 to 79 degrees directly in front of blower. Whereas a short distance away in temps were consistently 5 to 6 degrees cooler. Vaulted great room has 4 clerestory windows with no window blinds.

    We started using our room's fan late in the winter, thinking it would help bring the heat down from the vaulted space. However, I never gathered measurements to determine if the fan warmed the cold spots in the room. We have occupied our home only since last October.

    We will have blinds on the clerestory windows in our great room by next winter. That will help. But overall we have yet to achieve the ultimate winter comfort (except during sunny days, when the passive solar works great or when I am firing our wood stove) that my wife and I were seeking.

    We are eldery and place feeling warm at the top of our list of home requirements.

  6. rocket190 | | #6

    Randy, that is concerning. You aren't getting a good mix of air apparently. Do you run the fan on high speed, and how do you have your louvers controlled?

    I think that's the reason for having the remote thermostat. If you have warm air stagnating around the indoor unit, it will shut off before the center of your room is at temperature.

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