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Views on this HVAC equipment package? (specifically exterior sound)

orange_cat | Posted in General Questions on

For a 54,000 heat load as a upper target (with additional radiant heat in floor hydronic not mentioned here, so no concern about undersizing) and something like 35,000 cooling load, this is the equipment that we are considering installing. Zone 5 and need cold climate heat pump (air to air).

I have a very specific question about the outdoor unit: is there something similar but quieter?  Really need to keep the dBa low, but get 54,000 BTU heating.

Outdoor (one outdoor unit with 3 zones/branch box)
Outdoor   “MXZ-8C48NAHZ2-U1”
Indoor 2 and Indoor 3  (two of these)
4. Branch box with 3 zones 
5. Two ERV’s 

(I am trying to get details on the ERVs).

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  1. Eric_U | | #1

    If you were up for the cost and difficulty finding a place to buy one, you could try an air-to-water heat pump. Arctic, Daikin, Taco, Nordic, and Aermec are brands that offer them. I haven't looked at the spec sheet of every single one of those but a couple of the brands I've seen are as low as 30dB. I'm most likely getting the Daikin Altherma in a few months, which I think is around 40dB

    1. orange_cat | | #6

      I actually stopped considering air to water heat pumps because I could not find anything (of required size) as low as the unit here (54 dBa sound pressure, or just over 60 sound power). I am pretty sure all the ones you mentioned are higher (for the larger sizes - smaller ones are of course quieter)

      You need to pay close attention to how the sound measurement is reported (and it is *very* difficult to figure out how a particular manufacturer measures it. E.g. Daikin Altherma has 40 dBa- at supposedly 3m distance. Which at 1m becomes more like 50 dba. and Mitsubishi *seems* to be using 3 feet distance (roughly 1 meter) to report their measurements. A unit by another manufacturer had sound measurements taken at 10m distance (or was it 10 feet?). I remember being frustrated by how non-transparent it all is. And it is sound pressure, not sound power to further muddle the comparisons).

  2. Expert Member
    Akos | | #2

    I think the SM is a better option here. At least on paper it has better turndown:!/product/57011/7/25000///0

    The SM and 8c48 is almost the same equipment though, the SM is the new replacement for the 8C48, so not a huge difference. More info here:

    As for noise, these units are pretty much silent. I have an LG multi split next to a deck and don't even notice it. About the only time you'll hear it is in the middle of deep freeze when they ramp up to higher speed, even than it is still way quieter than any standard AC unit.

    Instead of the two smaller SEZ, I would go for a single larger PEAD unit. A bit more ducting but simpler install and less chance of having low load cycling issues.

    1. orange_cat | | #7

      Thank you. Cannot change the ducts or the indoor units - those were laid out when I realized I may look closer at the work of the mechanical engineer who designed the system (I did not look at the equipment size until then unfortunately, trusting that proffessionals know what they are doing. He was recommended!).

      TO be honest, I cannot even spot the differences between SM and the unit above. What am I looking for?

      (My noise concerns is not for me - I want to be code compliant on noise levels at the property line. We have a local code.).

      1. Expert Member
        Akos | | #8

        The SM is the current version of the 8c48, there is not much difference between them except that the SM support the Multicity specific indoor units as well.

        For a 5 ton unit it doesn't get much better than the low 50dB this is rated for, not sure you'll find something that much better. Rest are all pretty much around that mid 50dB range.

  3. walta100 | | #3

    When I read the posts from unhappy mini split owners, they all seem to have two things in common one the equipment is oversized and two the systems all have multiple heads connected to the compressor.

    Why the concern about exterior noise if the unit is running your windows will be closed and the units are unlikely to be audible indoors.


    1. orange_cat | | #5

      As for the oversized comment - I have joined this board because I thought my proposed equipment (not this one) was grossly oversized. With the help of this board and 3 mechanical engineers later this is as low as it got.So the "oversize" comment - I feel that one acutely.

  4. orange_cat | | #4

    The concern is the code. Some municipalities have noise limits. I need to be a certain decibel level at the property line to comply with it. It is not for me, it is to pre-empt neighbor's complaints.

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