Looking for the Best Minisplit Option
Planning a new house, two GBA readers decide that conventional ductless minisplit installations are unappealing, and suspect that filter changes would be a hassle
Ductless minisplit heat pumps have gotten many favorable reviews at Green Building Advisor, but Roy Goodwin sums up a concern that's popped up more than once: Despite their virtuoso heating and cooling performance, they're a little on the homely side.
"My wife and I are 69," Goodwin writes in Q&A post at GBA. "We're in the process of designing a house for our retirement with our architect. It's going to be a 'pretty good house' with a very small heating/cooling load. Neither my wife nor I think the ductless minisplits are all that attractive."
In addition, Goodwin adds, the air filters on a wall-mounted head could be a challenge to change because of their location. Ceiling-mounted ducted minisplits look like they'd present similar challenges and require a step ladder for filter changes. That's something they'd like to avoid.
Their 2,000-square-foot house will be built in the mountains of western North Carolina in Climate Zone 4. "We're looking for something like a conventional heat pump (ducts and all) with air filters that are easier to access," Goodwin says.
Any suggestions? That's the topic for this Q&A Spotlight.
Mount the unit lower on the wall, or directly on the floor
While the indoor units of ductless minisplits are usually mounted high enough on the wall to keep them out of the way, there's no reason they can't be lowered, GBA senior editor Martin Holladay points out. He includes a photograph of a unit mounted on an interior wall at roughly knee-height (see Image #2, below.).
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Its location might mean an occasional sore shin, but filter changes would be a snap.
Or, adds Dana Dorsett, choose a unit designed for installation on the floor. They look like small wall furnaces, he says, and like fin-tube convectors for hydronic heating systems most ductless floor units circulate air from the front face.
"They are easily set into walls or cabinets with the face pretty much flush with the wall," Dorsett says. Mitsubishi, in fact, publishes directions for embedding one of their units in a wall in such a way that its efficiency is unimpeded.
Fujitsu website includes specs for a universal floor/ceiling unit that can be mounted on the floor or just high enough on a wall to get a vacuum cleaner underneath. It can also go right on the ceiling, and the cabinets are just under 8 inches deep.
John Semmelhack refers Goodwin to a ducted Mitsubishi Mr. Slim model.
Factoring in higher static pressure
A complicating factor for Goodwin is how well these units would fare with high-efficiency air filters (those with high Minimum Efficiency Reporting Values, or MERVs). "We'd like to use something pretty high performance for dust as well as allergies," Goodwin says. "What about something like the Trane XV20i, which is variable capacity?"
Goodwin doubts the unit would ever run near its two-ton (24,000 BtuBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. /hour) rating, but it might be better prepared to handle higher static pressures that high-performance filters would create.
"Would running it at the low end on its rated capacity, using the variable-speed compressor, be less efficient?" Goodwin asks. "Would it have a negative effect on its life expectancy?"
Avoid systems that are grossly oversized
"In general," Dorsett replies, "modulating systems run at highest efficiency when modulating at or near their lowest speeds (effectively making the coils oversized for the amount of heat they actually need to exchange). So if your average heating loadRate at which heat must be added to a space to maintain a desired temperature. See cooling load. is around the minimum-modulated output, it can work out well, but if your peak load is below its minimum modulation, it becomes very sub-optimal."
When average loads fall below the minimum modulated output, he says, the system begins to lose efficiency to standby power use and surges in power consumption at startup and short-cycling. Similarly, minisplits that are more than 1.5 times as big as they need to be to meet peak loads will see a loss of efficiency, while below that they will operate at near optimal efficiency.
Keep in mind, though, Dorsett adds, that they're more expensive options than "right-sized" ductless systems and come with distribution losses that ductless systems don't have.
Further, adds Semmelhack, Goodwin should be able to use a high-MERV filter in any of the low-static minisplit systems on the market.
"Again," he writes, "it's a matter of system design/installation, and carefully accounting for the various parts of the system, including filters."
A two-ton unit would be much too big
Although Goodwin has yet to pin down heating and cooling loads, he describes a house with 2x6 walls filled with blown-in cellulose plus 2 3/4 inches of rigid polyisocyanurate insulation, an attic with 20 inches of cellulose, and insulation in both the foundation walls and floor.
Given these parameters, Dorsett adds, the heating load should be less than 20,000 Btu/hour, and could be less than 15,000 Btu/hour with good windows. This, he says, makes a two-ton, high efficiency ducted heat pump "a bit silly."
The Fujitsu 18,000 Btu/hour model would more than cover Goodwin's needs. An alternative would be a pair of floor units connected to a common compressor.
A dual-head unit might not be quite as efficient as the "best-in-class perfectly implemented" two-ton ducted model, but the installed cost would be less than half. Goodwin could spend the difference on rooftop solar, which would probably pay for most or all of the heating and cooling bill.
Our expert's opinion
We ran this one by Peter Yost, GBA's technical director, and here's what he had to say:
I am going to focus on the aesthetics of interior head in my response, just because people’s perceptions when it comes to technology fascinate me.
So, I sent out the following email to about a dozen or so colleagues and friends with the photo that you see at the top of the column:
Subject: Your input, please?
This may seem "mysterious," but please take a look at the attached photo and reply to me with whatever aesthetic considerations come to mind from the image.
When you reply, THEN I can share with you the nature of my request. Nothing scary, embarrassing, or illegal, and there are no correct or incorrect replies. All is relevant and correct, whether positive or negative in nature.
Thanks much – Peter
You can see that I was trying hard not to prejudice the issue of minisplit head aesthetics. When subjects of this “survey” responded, I sent them this followup e-mail:
I have been asked to comment on a Green Building Advisor blog in which an older couple thinks that the interior minisplit head (that white box on the right-hand wall is a conditioned air delivery system) looks homely.
So, I thought it would be interesting to ask folks from different walks of life and who have had longer and shorter walks (older and younger folks) how much they really noticed the head in a nice-looking kitchen with a lot of different aesthetics along the “old” and “new” lines. Just to see how much, unprompted, their eye was drawn to or affected by this homely head.
Now that you know the nature of the issue, if you still have interest, you can let me know what you think of the head, knowing that was the “target” aesthetic question.
Thanks much – Peter
And now for the results:
I got 12 responses, with respondents varying in age from about 30 to 65. The sample size was just too small to claim any differences in response based on age or their area of expertise (which ranged from building professionals to a sculptor).
Only 3 of 12 respondents mentioned anything about the interior minisplit head, and two of those three were more concerned with the “distracting” large open wall space just below the head.
There were some repeated themes:
- The white wall (where the minisplit head is) needs to be a color other than white.
- A shallow bookcase or something else should "fill” the space below the head.
- Artwork could be used to “fill” the large blank space. (In fact, the owners do have a piece of art there, hung shortly after this photo was taken.)
- I like/don’t like the mix of color and age of the ceiling beams.
- I love the daylightingUse of sunlight for daytime lighting needs. Daylighting strategies include solar orientation of windows as well as the use of skylights, clerestory windows, solar tubes, reflective surfaces, and interior glazing to allow light to move through a structure. in this kitchen.
- The range hood is distracting and/or it is too high above the cooktop to work right. (There were way more mentions of the aesthetics of the range hood than of the minisplit head).
- Specific aesthetic responses were all over the map, from “one of the ceiling planks is a different shade than the others” to “the white duplex outlet on the left hand end of the island should not be white” to “I love that etching of the owl.”
- I like how the photo shows the minisplit head AND the wood stove, another neat juxtaposition of “old” and “new,” a neat theme of this kitchen overall.
Of the 12 initial respondents, 10 followed up to say the hood is essentially unobtrusive, with about half knowing what it was from the start and half not.
So, I think the aesthetics of new technology, even something as “bulky” and “homely” as an interior minisplit head, can be more about the aesthetic context than anything else. And we can get desensitized to the aesthetic impact of the conventional and sometimes a bit hypersensitive to the new.
PS – On the difficulty of cleaning/replacing the minisplit interior head filters: You pop open the front grille and the filters are right there to slide in and out with ease.
- Image #1: Peter Yost minisplit
- Image #2: Fujitsu
- Image #3: Peter Talmage
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