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Musings of an Energy Nerd

Taking My Own Minisplit Advice, Finally

The Energy Nerd gets a cold-climate heat pump

Workers are preparing to install a Mitsubishi minisplit at my house. The outdoor unit will be installed on a concrete slab, a corner of which is visible in the photo. The slab is protected by a small roof. [Photo credit: Martin Holladay]

In a 2009 article titled “Heating a Tight, Well-Insulated House,” I advised builders to consider installing ductless minisplit heat pumps. At the time, these appliances were still relatively unknown in the U.S., so I provided an explanation: “A ductless minisplit is a type of air-source heat pump, so it can be used for heating as well as cooling. … These units can now be used for heating in very cold climates—even in Vermont, where winter temperatures reach -20°F.”

Since then, the use of ductless minisplits has exploded in this country. But the boom is just beginning: in North America, the minisplit industry has plenty of room for expansion.

Are you ready to install a cold-climate heat pump?

Over a year ago, my wife and I decided to install a ductless minisplit on our living room wall. (We had recently hooked up our formerly off-grid house to the local electric utility, a move that permitted us to consider using electricity as a space heating fuel.)

Since we’ve heated our house with a wood stove for decades, we’re used to point-source heat, and we’re comfortable with the fact that our bedrooms aren’t quite as warm as our living room. We haven’t given up on wood heat, but we needed a better backup heating system for the days when we might be traveling during the winter. Until recently, our backup heat source for periods of winter vacancy was a propane space heater. But our old Empire heater is somewhat unreliable—gusty winds have been known to extinguish its pilot light—and we decided that a ductless minisplit would be a more dependable method of keeping our pipes from freezing.

What brand should you choose?

Mitsubishi and Fujitsu were the first two minisplit brands to establish good reputations…

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  1. kyeser | | #1

    I think you'll find that the mini split will not keep your house warm at -20F. However at -10 to -15 it will produce heat. I heat with mini splits. We had a number of nights at close to 20 below last winter and our house cooled down into the lower 60's. By midmorning when temps had warmed up to closer to zero, the house got back up to temp, so it wasn't a big deal.

  2. robgood | | #2

    I’m in Duluth, Minnesota. I had a 48KBTU version of the same Mitsubishi product line installed with 5 head units on two floors. The house was adequately built in 1978 but is not tight by any measure; in part because of the large number of windows overlooking Lake Superior. The units were installed in October 2021, just in time for what was an early and relatively severe winter.
    Although the units produce useful heat at -15 F, it is at a very reduced efficiency as can be learned from Mitsubishi’s online spec sheets. I personally think windchill is a more relevant measure because although the units produce heat, their ability to produce enough heat is optimistically shown.
    I have three natural gas fireplaces and used them frequently. As a last backup, I have the legacy heating system which is radiant ceiling panels. I would not recommend anyone, especially in a remote area, rely solely on even top quality Heat Pumps in an climate which has air temps of -15 or WC of -20.
    That said, they are certainly useful in more moderate ranges. And the increasing variability of temperatures has meant I have several times used them for AC; something no one had in the Duluth of my youth. I will also counsel that unless you have a unfettered flow of air through all your rooms, a single head will not be enough. I made sure each living and sleeping area has its own head unit to allow local control and ensure no cold spots. Even with only two 1500 sf floors 5 units do not really cover the kitchen area. In the winter that is not an issue because of cooking and fireplaces. In the summer I would like an additional unit integrated with an HVAC system to remove cooking odors and supply 25% fresh air.

  3. frasca | | #3

    >> At our house, I’ve seen the thermometer drop to -30°F, but nights like that are rarer than they were a few decades ago.

    I've heard the case made that climate change is driving an increase in the frequency of extreme cold events, against the backdrop of a general warming trend. Good to learn that that does not seem to occurring in your region.

    Great write-up and I appreciate your perspective on working with contractors. I'd love to learn more about your foundation in a future piece.

    1. robgood | | #4

      This house is on a steep slope overlooking Lake Superior. The entry level is 1800 sf with anattached garage. There are two lower levels each 900 sf that are stair stepped. Masonry chimneys at each end help stabilize, piles go into the rock face. I will admit the floors of lower levels are a big heat sink. Eventually want to insulate and then top with wood flooring.

  4. Greg516 | | #5

    Great read, thanks.

    I’m interested to know what it’s like to clean one of the heads (standing on a ladder?) and for a follow up to track how quickly mold appears with your usage.

    I disassemble my LG inverter window unit after each cooling season to get rid of the mold and I’m hoping this task on a mini split is easier.

    1. pinewoodconcepts | | #6

      I have had mine serviced by a local company in Maine. They come and give both indoor & outdoor units a thorough flush with water and a cleaning solution. I didn't look over their shoulders too closely but they had a setup that minimized mess on the wall & floor of my house. Cleanup was minimal. And it was only a couple hundred bucks. Can't hate that once or twice a year :)

      1. Greg516 | | #7

        Good to know, thanks! I'd happily part with $200 to find a competent person to do this important but thankless task. I asked my installer about cleaning service and it was clear he wanted to avoid the topic.

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