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Community and Q&A

18k vs. 24k fujitsu minisplit

JTyler | Posted in Mechanicals on

I know these “help me size my minisplit” threads are becoming repetitive – sorry to add to the pile.

A manual J shows that an 18k btu unit should cover my heating needs (model 18rlxfwh). I am dealing with an installer who pushed a 24k btu unit at a pretty minimal up-charge: about $200 more for the larger unit. The recommendation is not based on any calculations, but I am wondering if there is any reason not to go with the larger unit.

If I am interpreting data correctly, the 18 modulates to 7kbtu, and the 24 to 7.5kbtu. Both should operate continuously during the majority of my heating season. The 24 has a higher cop of 13 vs. 12.3.

It seems like the larger unit is more efficient and modulates to an acceptable minimum, but with quite a bit more kick at the top end. Am I reading the data correctly? Missing anything?

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  1. Expert Member
    Dana Dorsett | | #1

    So, what are your calculated loads?

    For now ignore the COP numbers, which are taken at particular modulation levels, levels that may not be very relevant to your case.

    Can you point to online documentation for the models you are looking at, and can you share your location and outside & inside design temperatures?

  2. STEPHEN SHEEHY | | #2

    Assuming you are concerned about heating and not so much cooling, your design heat load is important. The 18K unit has a max heating output of 29kbtu; the 24k unit has a max output of 36kbtu. min output for both is about 7kbtu.

    If you drop down to the 15k unit (15RLS3H) max output is still 23kbtu, but min is 3.1kbtu and both SEER and HSPF numbers are better. For that matter, you can drop to 9 or 12k units and not lose much heat capacity (both are 22kbtu and modulate to 3.1) and get even better efficiency numbers.
    Finally, the nominally smaller units are signficantly quieter.
    You can get the Halcyon mini split 2016 full line brochure on line. It has all the specs.

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