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Mitsubishi mini split branch box efficiency

user-189027 | Posted in General Questions on

I currently have a Mitsubishi mini split system (MXZ-4c36NA) which supplies 4 units in my 1985  home (2 x MSZ-GE06NA, MSZ-GE12NA, and MSZ-GE18NA). It was installed mostly for AC, but we have really loved it for heating as well (Zone 5, New Hampshire), while still relying on our old oil heater for the coldest parts of the winter. Now our oil furnace is on it’s last legs (good riddance), so we are looking to switch entirely to the mini splits. We have solar panels and currently have a surplus/credit with our electric company. I will need to add a unit to the entryway which is currently not covered by the 4 units we currently have.

I had the original contractor come take a look and give me a quote on upgrading the outdoor unit to a Hyperheating one so we can use the system through the winter. I have not received his quote yet, but while he was here he said something that I have not found anywhere else. He said that I would be better off having 2 outdoor units so as not have to have a branch box, because the branch boxes are inefficient. Is that true? He specifically mentioned the defrost cycle, although I am not sure why the branch box would significantly influence that in a negative way.

On a separate but related note. If I do go ahead with this project, what does one do with the old but still functioning unit.

Thank you in advance.

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  1. Expert Member
    Akos | | #1

    If you look at:!/product/26173!/product/31973

    Which are the 3 zone non-branch box and 4 zone branch box, the 4 zone at cold temperature has higher COP. At least for Mitsu, the branch box doesn't effect efficiency.

    In your case, I would leave the existing no-hyper heat units, but get a pan heater for it (sold as an accessory). Then add in a single ducted hyper heat unit to replace your old furnace. Since you'll be running the two units together, the hyper heat can be much smaller than the existing oil burner and chances are you can re-use all the existing ducting.

    The non-hyper heat units have similar efficiency in cold weather just their capacity drops as you get bellow 15F.

    1. user-189027 | | #2

      Thank you for your response. It didn't make sense to me that the branch box would be a problem and I will look at the pan heater. Forgot to mention, but my furnace heats up via baseboards, so I don't think a ducted unit is for me, unless I misunderstood something.

      1. Expert Member
        Akos | | #3

        Replacing a boiler with a air to water heat pump is possible, but expensive. You can try pricing out something like the low temp Solstice unit from SpacePac.

        Replacing the oil burner with a resistance boiler is a nice option as you can keep it as a backup to run during a polar vortex event. If the existing mini split is up to do 90% of the heating job, just doing this (and no new heat pump) might be the cheapest option and not much more expensive to operate.

        The other option is to take out the rads and add in a dedicated wall/floor mount hyper heat unit in your main living space with the occasional electric baseboard in isolated rooms.

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