GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Adding a Zone with Older Compressor

rick20712 | Posted in Mechanicals on

I have a Mitsubishi MXZ-4B36NA that has been running flawlessly for the past 7 years. We live in Washington, DC so climate zone 4a. We have two zones (9,000 and 18,000) and are thinking of adding more.
Question 1: Can we get compatible air handlers or are they no longer available? I see in a compatibility chart that SEZ-KD09NA4  would be compatible but I have not found a supplier.
SEZ-KD09NA4R1 would seem to be the newer model but I’m not sure it is compatible with our existing compressor
Question 2: How much am I able to overrate the compressor? I’ve heard you can load 45,000 btu on a compressor rated at 36,000 btu but do not have a reference for that.

I appreciate any advice the community has to offer

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Akos | | #1

    The only people that can answer this is Mitsubishi. Give them a call.

    On most Mitsu units, you can install indoor heads up to 130% of outdoor unit rated capacity. To make sure, dig up the specification sheet of your 4B36, and see if your proposed setup is in the listed combination table.

    1. rick20712 | | #2

      Thanks for the recommendation. I didn't know it could be so simple :) The Mitsubishi rep let me know the current SEZ air handlers are all compatible with my compressor. Further, she confirmed the 130% over-rating. She was unable to provide data on the efficiency loss when operating in an over-rated capacity. I'll have to research that further.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |