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Actual average efficiency

GreenGiant117 | Posted in Energy Efficiency and Durability on

I’m trying to build a case to get the contractor who installed my heat pump system to rip it out and refund me… long shot, but I am hopeful.

One of the things I want to bring up would be the actual efficiencies of one to one systems that I could have installed (or likely self install)

I would replace two large outdoor compressors with 6 or 7 smaller ones handling basically identical Mitsubishi heads (FH06 x2, FH09 x2, and either FH12 x 3, or FH12 x 1 and FH18 x 1)
On paper the two outdoor units have MAX SEERS of 18 and 20, whereas the one to one’s have SEERS of 33.1 all around.
I want to provide data showing a comparison of the amount of power being consumed at 18 and 20 vs 33.1, but I want to do it somewhat fairly and skewed towards them so they can’t say that I am providing completely false data.

Based on what I can find the calcs for SEER savings is this (in general):
Savings = (higher seer/lower seer-1)*100
Which under ideal circumstances would translate to:
18 SEER: 83.8% electricity savings
20 SEER: 65.5% electricity savings


I understand that this is under ideal circumstances, but I was wondering if there was some way to calculate out a (very) rough average SEER that the one to one units would run at?

Even running the calculations as though the one to ones run at 25 SEER on average I would still see 25-38.8% savings…

I live in New England so it does get fairly cold here so I understand it won’t be 100% efficient all the time. I just don’t know how to word the search to find this information.



  1. paul_wiedefeld | | #1

    Ha good luck. Multi-splits can be inefficient, that is undeniable. The Green Architects' Lounge podcast has an episode with a Mitsubishi guest explaining why multi-splits struggle so much when oversized.

    However, SEER is a cooling efficiency metric and you're in a heating-dominated climate so SEER differences won't be convincing.

    1. GreenGiant117 | | #2

      That's fair, so I guess it would be via HSPF ratings?
      Which would still be something like 15-20% more efficient...

      1. paul_wiedefeld | | #3

        That's efficiency testing based on proper sizing, which if you have 7 indoor heads hooked up to 2 outdoor units, you're almost guaranteed to be oversized. I agree your contractor chose the less efficient option but I'm not convinced they'll refund you.

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