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Community and Q&A

Fujitsu wired thermostat dilemma

davidsmartin | Posted in Energy Efficiency and Durability on

This fall I installed a Fujitsu mini-split installed (AOU15RLS3H with ASU15RLS3) in my Vermont house. I have been frustrated that the temperature at the unit (near the ceiling) is higher than the rest of the room and that the temperature difference varies depending on the outside temperature, whether the insulated window shades are drawn and the amount of sun coming in the south windows. So I decided to spend the $450 for a wired remote. Then I learned that with the wired remote I will lose the ability to set the thermostat below 60 degrees — currently when the house is empty for a week or two I can set it at 50 degrees.

So it seems I that if I choose the wired remote to get a comfortable temperature without changing the thermostat constantly I will have have to waste money by over-heating a vacant house.

(1) Is there any way to get a remote thermostat without sacrificing the ability to turn down the heat below 60?

(2) I am building an addition that will have its own mini-split. Is the best solution to get a floor standing unit, so that the measured temperature will be close to the one felt by people in the room? Or would a ceiling fan move the air around enough to equalize the temperature?

(3) Do Mistubishi units have the same problem?

(4) Is there any chance that manufacturers will figure out that while having the temperature sensor in the unit, close to the ceiling probably works OK for an air conditioner it does not work well in a heater?


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  1. STEPHEN SHEEHY | | #1

    Dave: how close to the ceiling is the unit? I have a similar unit, 12RLS3H, mounted about 9' high on the wall, but about 18-20" below a sloped ceiling. I don't have the problem you describe. I have the remote set at 68° and the air temp stays right at 68° unless the sun is heating up the room. Vanes are pointed downward. Outside temps don't seem to matter at all.

  2. davidsmartin | | #2

    Stephen -- the unit is only 6" below the ceiling. And to make matters worse, the ceiling has exposed 4x10 beams, so that warm air is trapped between the beams. I wonder if lowering the unit by 12" might make a significant difference?

  3. STEPHEN SHEEHY | | #3

    Lowering it might help, but I'd check with Fujitsu and see what they say. I'd think lowering the unit would be a considerable bother. I just looked at my installation manual and it only requires 3" below the ceiling.
    Regarding the thermostat issue, can you shut off the thermostat and just use the remote? $450 for a thermostat? Yikes!

  4. GBA Editor
    Martin Holladay | | #4

    As you probably know, researchers have discovered that when the indoor unit of a ductless minisplit system is installed close to the ceiling, higher return-air temperatures lower system efficiency.

    As Robb Aldrich noted, “We definitely saw high return-air temperatures. Some of these indoor units were installed just 4 inches from the ceiling, and that type of mounting can contribute to high return-air temperatures — higher than the temperature at which these units are rated, which is 65°F.”

    If you or other GBA readers missed the article in which I quoted Aldrich about this issue, here is the link: Ductless Minisplits May Not Be As Efficient As We Thought.

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