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Quotes on minisplits

Muddytyres | Posted in General Questions on

Revising my house heating/cooling upgrade. Four HVAC contractors went out.

1. Mitsu diamond dealer. Three units total- MXZ3C30NAHZ(two of these) and one MXZ2C20NAHZ, 2 5 port branch boxes, 11 HH highwall units total(different types) 1 floor console.  Does not need upgrade of current electric box. Has a less expensive option that leaves basement at the mercy of the current EBB

2. Local HVAC- has done some minisplits, can get mitsu- six units total
 4- MXZ8C48NAHZU1, one MUFZKJ12, one MUFZKJ12 and 15 inside units (many different ones listed) no branch boxes noted in this one. Required upgrading my electric to 400amps

3. Minisplits are impossible

4. Can do minisplits, will give me a quote based on cost of estimated hardware, but not sure where units will be placed or configuration will be.

SOOO- is this common? I know this house is more than a little challenging but heck, there’s a house worth of difference in the supply!  Is there some other way that I should be going about getting these estimates?

https://www.realtor.com/realestateandhomes-detail/193-Loop-Road-Loop_Davis_WV_26260_M48691-09209

Oh- here’s a link to the house. And FYI- this is an older pic and the arch part of the sunroom is now gone and the room is half the size with a deck.

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Replies

  1. Trevor_Lambert | | #1

    Most, probably almost all, HVAC contractors know nothing about design. What makes this worse is that they all think they do. Get a professional design from a qualified designer, then give that to the contractors to quote on.

    1. Muddytyres | | #2

      How do I find a qualified designer? The one contractor was off the Mitsu website...

  2. john_heckendorn | | #3

    Sara, what's the house's current HVAC setup?

    1. Muddytyres | | #8

      Electric baseboard of questionable integrity

  3. Expert Member
    Dana Dorsett | | #4

    Start with an independent Manual-J type load calculation, or run your own room-by-room IBR type load calculation using a spreadsheet, or an online Manual-J tool such as Loadcalc (https://loadcalc.net/index.php) .

    https://www.greenbuildingadvisor.com/article/how-to-perform-a-heat-loss-calculation-part-1

    https://www.greenbuildingadvisor.com/article/how-to-perform-a-heat-loss-calculation-part-2

    Be aggressive on the air tightness assumptions or either method is going to overshoot reality by quite a bit.

    I suspect the 99% design temp in Davis is about +2F (yes I know it gets a lot colder than that), base on the 99% design temp in Elkin of +5F, about 1000' lower in elevation than Davis. It would be fine to use 0F too.

    Most reasonably tight 2x4 framed 3500' houses with clear glass double pane windows and reasonable insulation levels will come in between 50-60,000 BTU/hr @ 0F. Most reasonably tight code-min 2x6 construction houses that size with low-E windows will come in around 40-45,000 BTU/hr @ 0F. These are totally do-able with cold-climate mini-splits. The MXZ-8C48NAHZ is good for 54,000 BTU/hr @ +5F, and has a capacity table down to -13F. If the actual load @ 0F is under 50K it would have margin without the MUFZ-KJ12 (good for over 12,000 BTU/hr @ 0F ) or the MUFZ-KJ15 (good for over 17,000 BTU/hr @ 0F.)

    http://meus1.mylinkdrive.com/files/MXZ-8C48NAHZ_Submittal.pdf

    https://ashp.neep.org/#!/product/29012

    https://ashp.neep.org/#!/product/25892

    https://ashp.neep.org/#!/product/26096

    The MXZ-3C30NAHZs are good for over 25,000 BTU/hr EACH at 0F, and the MXZ-2C20NAHZ is good for over 20,000 BTU/hr,:

    http://meus1.mylinkdrive.com/files/MXZ-3C30NAHZ2_ProductDataSheet.pdf

    https://ashp.neep.org/#!/product/26173

    http://meus1.mylinkdrive.com/files/MXZ-2C20NAHZ_Submittal.pdf

    https://ashp.neep.org/#!/product/29555

    Both proposals seem a bit oversized, but it's hard to say with certainty. Without the room by room load numbers along with the whole-house load number it's hard to know if the proposals make any sense at all.

  4. Expert Member
    Dana Dorsett | | #5

    (My lengthier response seems to be lost in administrative purgatory, so I'll break it down in chunks.)

    Start with an independent Manual-J type load calculation, or run your own room-by-room IBR type load calculation using a spreadsheet, or an online Manual-J tool such as Loadcalc (https://loadcalc.net/index.php) .

    https://www.greenbuildingadvisor.com/article/how-to-perform-a-heat-loss-calculation-part-1

    https://www.greenbuildingadvisor.com/article/how-to-perform-a-heat-loss-calculation-part-2

    Be aggressive on the air tightness assumptions or either method is going to overshoot reality by quite a bit.

    I suspect the 99% design temp in Davis is about +2F (yes I know it gets a lot colder than that), base on the 99% design temp in Elkin of +5F, about 1000' lower in elevation than Davis. It would be fine to use 0F too.

  5. Expert Member
    Dana Dorsett | | #6

    Most reasonably tight 2x4 framed 3500' houses with clear glass double pane windows and reasonable insulation levels will come in between 50-60,000 BTU/hr @ 0F. Most reasonably tight code-min 2x6 construction houses that size with low-E windows will come in around 40-45,000 BTU/hr @ 0F. These are totally do-able with cold-climate mini-splits. The MXZ-8C48NAHZ is good for 54,000 BTU/hr @ +5F, and has a capacity table down to -13F. If the actual load @ 0F is under 50K it would have margin without the MUFZ-KJ12 (good for over 12,000 BTU/hr @ 0F ) or the MUFZ-KJ15 (good for over 17,000 BTU/hr @ 0F.)

    http://meus1.mylinkdrive.com/files/MXZ-8C48NAHZ_Submittal.pdf

    https://ashp.neep.org/#!/product/29012

    https://ashp.neep.org/#!/product/25892

    https://ashp.neep.org/#!/product/26096

  6. Expert Member
    Dana Dorsett | | #7

    The MXZ-3C30NAHZs are good for over 25,000 BTU/hr EACH at 0F, and the MXZ-2C20NAHZ is good for over 20,000 BTU/hr:

    http://meus1.mylinkdrive.com/files/MXZ-3C30NAHZ2_ProductDataSheet.pdf

    https://ashp.neep.org/#!/product/26173

    http://meus1.mylinkdrive.com/files/MXZ-2C20NAHZ_Submittal.pdf

    https://ashp.neep.org/#!/product/29555

    Both proposals seem a bit oversized, but it's hard to say with certainty. Without the room by room load numbers along with the whole-house load number it's hard to know if the proposals make any sense at all.

  7. Muddytyres | | #9

    THANKS! I'm working on air sealing. There is a TON of glass in this house- framing is 2x6 and there are a ton of holes that I'm working on, I am planning on doing a blower door after we get the current obvious problems dealt with.
    I would, very literally, have to do the Manual J myself but I was trying to use the app that does something similar, but I don't know enough about the components to supply the info needed.
    Interestingly, the Contractor that said 'it can't be done' is the only one that does a manual J.

    1. Expert Member
      Dana Dorsett | | #10

      >"Interestingly, the Contractor that said 'it can't be done' is the only one that does a manual J."

      As a general rule Manual-J's performed by contractors are usually full of errors to the UP-sizing end compared to those performed by engineers.

      >"There is a TON of glass in this house..."

      Probably literally, a ton of glass, if double-glazed. Have any idea about the glazing specs? (clear glass, Low-E glass, gas filled, etc..)

      Another freebie/cheapie Manual-J tool out there that can probably handle this house credibly is CoolCalc:

      https://download.cnet.com/Cool-Calc-Manual-J/3000-20417_4-76303640.html

      I've seen pretty bizarre load numbers from that tool when applied to non-standard construction, but if this is a 2x6/R19-R21 type house with ordinary window types you should be able to get there.

  8. Muddytyres | | #11

    Thanks! I started the cool Calc, and didn’t know enough to use it. I’m going to give it a shot again this weekend...we’ll see...

    Is it common to have to upgrade to 400amp service? Two of the quotes required or included upgrade to 400, the third did not..

    1. downtowncb | | #12

      If the house is currently able to be adequately heated with electric baseboard heating I can't imagine it needs a supply upgrade to run heat pumps which should use on average 1/3 or less of the power to do the same job...

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