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Cold-Climate Minisplit Recommendations

JIM BAERG | Posted in General Questions on

Hi friends,  I’d like suggestions on make/model of minisplit for a house  currently under construction.  The owner is a retired widow with limited funds and income.
Location and Climate:  Livingston, MT  6700 – 8600 HDD, 260 CDD. Design temp is -14 degrees.  Very dry climate and windy (winter)
House: 1182 sqft exterior, 1015 sqft interior, Zero Energy type, R-30/44/60, U-.23 Vinyl casement windows (curtains to be added), air tight,  Manual J is at 14k.  Floor plan is open, single story with unheated, insulated basement.  Attached greenhouse (south side) is thermally isolated from the house.
Ventilation:  range hood to ext., 2 speed Panasonic bath fan for ventilation.
Heating: preferred system is a single head mounted in the Kit/Din/LR area with some electric resistance in the bathroom.
We have experienced Fujitsu and Mitsubishi dealers in the area with the usual attitudes about sizing, etc.

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  1. GBA Editor
    Kiley Jacques | | #1

    That sounds like a great project--it's so rare to see small and thoughtful new houses being built. GBA has some information sort of spread around the site that sheds light on pros and cons of different air-source heat pump minisplit systems. Start with this article and follow some of the links: Heating a Tight, Well-Insulated House.

    Here's an excerpt:

    The nominal heat output rating of a ductless minisplit is calculated at an outdoor temperature of 47°F. Since the unit’s heat output drops with the outdoor temperature, it’s important to check low-temperature performance before specifying a unit. For example, the Mitsubishi Mr. Slim Hyper-Heat unit (model PUZHA36NHA) has a nominal heat output rating of 38,000 Btuh. According to the manufacturer, at an outdoor temperature of -13°F, its heat output drops only 21%, to 30,000 Btuh.

    Another ductless minisplit, the Quaternity unit from Daikin (model FTXG15HVJU), has a heat output rating of 17,890 Btuh at 43°F. At -4°F, however, its heating output drops to 7,310 Btuh.

    As long as the heating system designer sizes the unit so that it will meet the building’s heating load at the design temperature, there’s no reason it won’t keep a home comfortable — even when the temperature drops well below zero.

  2. Trevor_Lambert | | #2

    I think an HRV would be justified in this design, and based on the numbers provided I question whether the appropriate amount of ventilation heat loss was accounted for in the calculation. Seems to me that 50cfm at -13F and 0% heat recovery would chew up a sizeable amount of that 14,000btu/h, though I didn't do the calculation.

  3. joshdurston | | #3

    Since you adding some electric, you have the opportunity to keep things pretty tight and maybe avoid the big jump in min modulation that you see at some points in the sizing grid.
    14kbtu seems a bit low for a heating load though.
    You may want to consider 2 smaller 1:1 units rather than 1 2ton unit, for low min modulation/redundancy and even distribution. In shoulder seasons you can turn one off and get a lower min output. For truly cold climates the Fujitsu's should be a top contender since they continue to run, even when below the min OAT rating.
    The setpoints should be carefully coordinated with the electric / hp to avoid biasing the load towards electric inadvertently. Since she has an unfinished basement, I would recommend a small ducted unit, the electric heater could be integrated with the hp controls as a second stage.

  4. paul_wiedefeld | | #4

    You’ll be fine with the name brands: Mitsubishi, Fujitsu, etc. I’d focus on service and part availability as many brands make a cold climate 12,000btu unit. I’d also put baseboard throughout the house, it’s cheap, redundant and covers you for all temperatures. Many have posted good experiences on GBA using the appropriate wall mounted thermostat vs the remote control.

  5. Expert Member
    Dana Dorsett | | #5

    The Mitsubishi FS18 is about right for your design load, with 17K output @ -13F, a bit less when derated for altitude:\M_SUBMITTAL_MSZ-FS18NA_MUZ-FS18NA_en.pdf!/product/34433/7/25000///0

    A down side to Mitsubishis is they can and will shut down somewhere around -20F, and won't re-start until it warms up to -13F or so. (Read the fine print on the submittal sheet.)

    The Carrier /Midea 38MARBQ24AA3 gets you there too:!/product/36689/7/25000///0

    I don't have the extended temperature chart in front of me, but I'm pretty sure the Fujitsu AOU/ASU-H18LMAS would get you there too:!/product/57041/7/25000///0

    Of those three I prefer the Carrier/Midea's defrost ice management the best, since it turns off the pan heater 5 minutes after a defrost cycle is complete. Given the number of hours it's below freezing in Livingston every year those savings add up. But if there is better local support for Mitsubishi & Fujitsu don't sweat the defrost stuff too much

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