It’s well known that a single zone ductless system has extremely high efficiency. I’ve seen advertisements for SEER 20 or SEER 30 systems. My question is what is the SEER rating for a multihead system. Can the larger condenser really cycle down to only output the BTU/hr needed for a smaller room while keeping the higher SEER? How does this then compare to say high velocity AC?

1 Answer 1


The type of motor control is where the efficiency is gained. Variable frequency drives (VFD) can reduce the speed when needed thus using only the amount of power needed so a multi port compressor can maintain a high efficiency with this type of control.

  • Right but can the systems maintain a constant SEER?
    – rhl
    Jul 4, 2018 at 10:33
  • If you want an absolute answer you will never see the seer that the unit is rated for. The testing is done under laboratory conditions of both temp and humidity. So No and that answer is true for central air systems also.
    – Ed Beal
    Jul 4, 2018 at 14:48
  • I don’t think you understand my question. They only ever publish one number. Multi zone systems have lots of ways to run with varying BTU loads. I presume in this case SEER/EER numbers are best case, not worst case. My question is how much worse can it get ?
    – rhl
    Jul 5, 2018 at 15:00
  • I do understand you have to look up the testing method and conditions. Some units are only tested at a full load, some are tested under a variable load (more accurate). It depends on the brand and model. Some will provide the efficiency some will never get close. So there is no absolute answer, I find the higher end units usually much more expensive to have the most accurate rating, many of the cheaper ones barely make there rating under lab conditions optimized for that model.
    – Ed Beal
    Jul 5, 2018 at 15:09
  • I see. Perhaps you have any example of where there is more than one test published ?
    – rhl
    Jul 6, 2018 at 1:56

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