Image Credit: Image #1: Peter Yost minisplit
More Q&A Spotlight
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.).
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,…
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33 Comments
No discussion of radiant cooling?
I know radiant cooling is not really used here in the south, but with operating savings over conventional AC, the ability to cool individual rooms (allowing you to close doors), and incorporation of a dehumidifier, maybe it is time to revisit the idea.
Response to Donald Endsley
Donald,
I think that the idea that a radiant cooling system uses less energy than an air conditioner is an urban myth.
The topic of radiant cooling comes up about every 6 months on GBA. Here are links to some recent threads:
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/27947/radiant-cooling-more-efficient-alternative-fo
https://www.greenbuildingadvisor.com/community/forum/mechanicals/23308/are-there-efficient-slab-radiant-systems-also-cool
Mini Splits
We design a lot of homes with mini-splits and found the efficiency and the ability to really zone creates overwhelming value. And if a ducted system were actually put in correctly and it was balanced correctly the owner would probably complain when you told them they were not allowed to put furniture where they wanted to make it work correctly. If you look at a project and start using interior walls put the heads where they work and not right where they look. We actually took several homes and found out the space a head takes up verses the white space of grill covers on a ducted system averages almost 65% less to look at just depends at what you are looking for.
LG Art Cool
Sorry if someone already mentioned this:
http://www.lg-dfs.com/art-cool-single-zone.aspx
I think it would be quite a fun conversation piece.
Covers are available
I think they look pretty good:
http://www.shuttershack.com/~shutter/products/radcovers/wood-radcovers.htm
More on the LG Art Cool
Hmmm... It's a fan-coil unit for a ductless minisplit system that includes a frame where the homeowner can slide in their favorite poster or photograph.
I imagine that the "I hate the appearance of minisplits" crowd might want one of these.
.
Another image of the Art Cool unit
Here's another image.
I can't imagine that the unit has the same "throw" as a conventional unit. The air flow restrictions probably reduce efficiency somewhat.
.
LG Art Cool
The LG Art Cool units definitely take a performance hit in exchange for the look. 8.2HSPF and 16SEER on the 9k single-split system.
The discharge air is from the top and the sides, I think.
Missing the point?
Did the homeowners really mean *only* aesthetics when they said:
"Neither my wife nor I think the ductless minisplits are all that attractive."
Could it be that they had already actually looked at the pros and cons beyond aesthetics? Could it be they wanted a 3Bed 2Bath home with a home office etc? I know it's hard to believe. And probably stunning to imagine they *wanted heating and cooling in every room*! The audacity.
Could it be they didn't want the ambience of a holiday inn Tokyo with a nice whirring companion every evening?
Well, we know that the whole HVAC industry has NOT completely FAILED to provide a solution for a typical human USA home. No it's clear there is no confusion whatsoever here. The entire problem is the homeowners!
Just go ahead and ban me. Please.
oh i'm sorry ..
Are we SERIOUSLY discussing the aesthetics of mini-splits here ??
Response to Eric Wahl
Eric,
Q. "Could it be that they had already actually looked at the pros and cons beyond aesthetics?"
A. Yes, it's possible. But it is certain that they mentioned aesthetic objections to minisplits -- "Neither my wife nor I think the ductless minisplits are all that attractive" -- so it is valid to respond to that issue.
The house in question is... (response to Eric Wahl, post #9)
"It's going to be a 'pretty good house' with a very small heating/cooling load"
"...2,000-square-foot house will be built in the mountains of western North Carolina in Climate Zone 4."
By 'pretty good house', in the parlance of GBA and others it's something akin to R5/R10/R20/R40/R60 for windows / basement slab / foundation walls / above-grade walls / attic, respectively. In a zone 4 location a house like that will have a design heating load well under 20,000 BTU/hr and probably under 15,000BTU/hr, which is well below the output of even a 2-ton ducted heat pump at the 99% outside design temp in a climate zone 4 location.
While it's true that "...the whole HVAC industry has NOT completely FAILED to provide a solution for a typical human USA home", they're pretty much a complete fail when it comes to the atypical, higher performance home under discussion here. (It's arguable that the US HVAC industry also pretty much failed better designed IRC 2012 code-min houses too, though not as abjectly.)
At 'pretty good house' it actually IS "...stunning to imagine they *wanted heating and cooling in every room* ", unless they simply don't understand just how low the room-to-room delta-Ts will be, even when point-source heated/cooled. Experience indicates that a 'pretty good house' can be comfortably heated and cooled with a single mini-split head per floor even in climate zone 6 locations.
The concept of needing "... heating and cooling in every room..." became enshrined in code back when typical windows were single pane R1 and leaked air, houses were built with no wall insulation and you were lucky to have R11s in the attic.
Current codes now require that the heating systems be able to achieve 68F in every room at the 99% outside design temp, but does not specify that every room needs a separate heat emitter. With U0.2 /R5 windows and R40 walls the notion that each room needs a duct register to meet code or to provide heating/cooling comfort simply isn't the case, especially if the house is designed with point-source heating & cooling in mind. Big unshaded east or west facing windows in doored off rooms remote from a ductless head can be a cooling season comfort issue in a pretty-good house, but it's just as easy to design those problems out as it is to design it in. In this case they were actively " ...in the process of designing a house...". which is the perfect time to manage those issues.
I helped a friend retrofit an 1890s antique up to "pretty good house" levels, now heated/cooled with a single ductless head per floor in a climate zone 5 location (99% outside design temp of +5F at that site). The only room with a comfort issue was an east-facing bedroom on the third floor that got too much early-AM solar gain around the summer solstice (resolved with an exterior shade.) All rooms on a given floor stay within 5F of one another even when temps drop in to the negative digits (which happens a few times per year in that location, despite the +5F design temp.) Concerns about needing room by room heat / coolth emitters have proven unfounded.
The notion that current model mini-splits are in any way comparable to "...the ambience of a holiday inn Tokyo with a nice whirring companion every evening" is also completely unfounded. Mini-splits are much quieter than a hotel PTHP/PTAC unit. A typical new-school Fujitsu or Mitsubishi 1-ton mini-split at max blower speed is quieter than most refrigerators, and barely audible at low speed, which is where it will run most of the time. (If only ducted solutions were as quiet! )
Bottom line, this isn't a typical house with typical loads, and mini-split solutions are probably going to be appropriate here. Using floor mounted cassettes addresses filter swapping even if wheel-chair bound issue, and probably the aesthetic issue as well, since they can be mounted flush with the wall, just like a register grille.
Dana, I am particularly interested in how you sized and located the mini splits in your friends' antique house - I'm trying to decide how to cool my "pretty good " 1771 3 BR saltbox which I restored 3 years ago here in CT. I too have grown frustrated by the "rule of thumb" contractors who don't seem interested in sizing the cooling system properly and are even less interested in specifying how to locate head units or ducted mini-splits to retain the character of the post and beam with restored plaster walls and ceilings..
The house has R26 walls, R52 in the attic ceiling as well as R60 in the rear dormer roof. I chose for historical reasons to restore the original wavy glass single pane windows with external wooden storms everywhere except the south facing walls which have Argon filled U.31 windows. Heat is a combination of Radiant and original Cast iron radiators, so I'm only concerned with using efficient energy conscious AC technology - leading me to hidden mini-split technology to not destroy the original character of the house. Underfloor in the basement is possible for the 1st floor, or similar in the attic as well, but though there's lots of advise on the GBA forum, nothing I've found yet can point me how to design the system. I've done the room by room cooling load calculation, and your comments above about using a single ductless head unit per floor is intriguing! The more I keep reading I get more questions - return air, zoning, per room delivery, distribution within the rooms of each floor - etc..
Can you advise on guidelines for designing this or where to go to read more? The house is approx 800 sq ft per floor, and all I keep thinking is that there has to be a better way that doesnt need ducts and head units per BR that will simply cool each floor! Thanks in advance
Gary
Can't Teach An Old Dog New Tricks
Apparently Eric Wahl is set in his HVAC ways and that is the way some people are. I know contractors that still tell me that houses need to breathe through the leaky walls. Maybe ductless mini splits aren't for everyone and that is OK. But for those who want a 22 SEER+ unit that is extremely energy-efficient and quiet, then minis are for them.
In all the homes I have lived in where there was HVAC duct work (professionally installed), I had cold and hot rooms, the units would freeze me for 15 minutes and then I would get hot 20 minutes later. I've paid for this energy penalty of having duct work snake and wiggle through walls and ceilings and 150F attics. My pocket book paid the price for these ducted units and the A/C installers loved building those ducts and dropping a 5 ton unit in a 2,000 sqft home.
As Dana stated, " they're pretty much a complete fail when it comes to the atypical, higher performance home under discussion here" and "the US HVAC industry also pretty much failed better designed IRC 2012 code-min houses too, though not as abjectly."
We are discussing high-performing homes, not code minimum builder spec homes. Ductless minis and a highly-insulated home are a match made in green heaven. HVAC ducts and a code minimum home are a match made in high utility bills for the next 50-100 years. The choice is yours and sometimes an old dog needs to be left to his own ways.
Code min is better than you might think (response to Peter L) )
"HVAC ducts and a code minimum home are a match made in high utility bills for the next 50-100 years. "
IRC 2012 code min homes that have actually been blower-door tested & inspected aren't nearly the energy pigs of the typical circa 1978 code min home.
The HVAC industry has barely clued into that fact though, with even smallest-of-the line available heating equipment being 2x overwsized for the loads of an average house, and contractors regularly up-sizing it considerably from there (just in case it might get down to -187F during a cold snap or something :-) ). There's a comfort hit and some amount of efficiency hit from that type of oversizing, as well as an up front bite in the wallet.
In US climate zone 4, with judicious layout and careful attention to window sizing & in doored off rooms it's possible to heat adequately with point source heating like ductless mini-splits at IRC 2012 code min R values / U-factors. In zone 6 it gets to be a lot tougher at code-min, but still pretty easy to make it work at "pretty good house" levels, which runs about 1.5-2x the performance of code min overall. At "pretty good house" levels the windows are only about 1.5x IRC 2012 code min for zone 6, the walls about 2x, and the attic about 1.2x.
http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_11_sec002.htm
But it's an even bigger multiplier over code-min for climate zone 4, where Roy Goodwin lives.
Sooo Hard to Change
Dana's comment cuts to the core of the biggest problem:
(Today's homebuyers and most builders and HVAC contractors) " simply don't understand just how low the room-to-room delta-Ts will be, even when point-source heated/cooled. Experience indicates that a 'pretty good house' can be comfortably heated and cooled with a single mini-split head per floor even in climate zone 6 locations"
Everyone spread the word: https://www.greenbuildingadvisor.com/blogs/dept/musings/just-two-minisplits-heat-and-cool-whole-house
Question for Dana
Given how efficient and inexpensive ductless MSHP units are, what do you think about building a set of guidelines for what would be necessary to heat and cool a house using the one-head-per-floor rule? As you allude in Comment 14, Pretty Good House levels of insulation are overkill for Zone 4, and I presume they would also be in Zones 1-3. PGH levels are cold-climate-centric in my opinion.
From spenidng time in my parents' code-built house in San Antonio, air tightness and window placement are far more important in warm weather than wall R-value. I plan to build on zone 4 in the next five years or so, and my plan is to build the envelope just good enough so I can comfortably use minisplits,then put the money saved in not overbuilding the envelope into PV panels on the roof.
My experience with mini splits
I put 3 Mr Slim units in my house several years back before it was renovated - many single glazed windows, not much insulation - to replace an ancient floor furnace and 3 window AC units. I had enjoyed the room by room control so I went with a non ducted system instead of a traditional HVAC system. They worked fine for many years (as they still do). Interestingly, since I renovated my house, replaced some windows, added storms, and insulated and air sealed, I can pretty much condition my house with only one unit running. The delta T between rooms is minimal, in fact, right now it's 91 outside and between 78 and 81 inside with 1 unit running at a very low speed. I find that I run the living room unit if its hot at night, and with a ceiling fan in my bedroom I'm perfectly comfortable. If my kitchen is crowded and I'm cooking, turning that unit on will keep it comfy. The comments about noise are interesting, since the ductless units are typically quieter than most ducted HVAC systems except possibly when running at their highest velocity. As to differences between rooms, I agree with the comment above about ducted systems not providing consistent heating and cooling - ducts are no guarantee of even conditioning. A good envelope and point source heating and cooling should work fine for most people, it just takes some getting used to. Putting units in each room provide for excellent zone control, but they do get pricey as you are paying for significantly more capacity than you need. I would love to see minis with a max of 3-4K btu capacity but I expect that there wouldn't be much savings. Aesthetics aside, people just need to acknowledge that ducted systems won't necessarily give you more even conditioning than point source equipment - especially given the state of residential HVAC installations (at least the ones I have seen). Other than putting in more capacity than I need, I'm quite happy with my "ugly" wall mounted minis. Would definitely use them again.
about temp detal between rooms ..
I currentl heat my house with 4 9Kbtu Fujis.
They are located at each end on each floor.
It's been a year now, and i have yet to notice more than 1c of difference between any rooms in the house . That is through heating winter time and cooling sunny summer.
The house is ( unfortunately ... ) 60' long and ~ 40' wide.
I can't see how a more reasonably sized home ( let's assume 40'X30' ) would have problem with using only 1 unit per floor .
That makes for a pretty cheap climate system @ 3-4K$/unit installed.
Response to Martin Holladay
Martin your post made me look a bit deeper into the subject of radiant cooling. I also should have been a bit more clear as I meant conventional ducted forced air AC. In my searching I apparently ran across Dr. Mumma's life work on the subject. It seems to me the operational savings come from pumping water instead of air, and the ability to run a higher dry bulb air temp. I must say I am rather attracted to Dr. Mumma's approach. He advocates using a Dedicated Outdoor Air System (an ERV basically, but not exactly) for ventilation, humidity and latent load control, and radiant cooling for the sensible load. He also advocates using Dew Point Temperature (DPT) sensors to help control the radiant panels. This appeals to me for a number of reasons. One: it's less filters to change. Two: I'm a fairly private person, call me quirky but I prefer to sleep with the door to my bedroom closed. since this likely wouldn't be a point source system shutting the door just isn't an issue. Three: with the DPT sensors, at least in my mixed humid climate, I will have an indication when my ventilation system is not working correctly as my cooling system will shut down. I'm not sure Dr. Mumma's approach works with residential ventilation rates, but the approach is very appealing to me.
Response to Donald Endsley
Donald,
While in theory a radiant cooling system can be designed in a way that assures that the system is energy-efficient, the required engineering expertise and equipment are not available for residential-scale installations. That's why these systems aren't cost-effective.
In most cases, it's hard to beat ductless minisplits for residential applications if you care about (1) initial equipment costs and (2) operating costs.
how about combining both
I'm headed in this direction. Combing radiant heat and cooling with the mini-split as I remodel. I'm planning on using the radiant as more of a secondary system, not intending for it to be my primary source of temp control, but providing some help for better equilibrium and also for providing peak help, mostly during those -20 degree winter nights.
It's not cost effective though unless you DIY and even then break even may only be the reality. Also helps if you have access to cheap water and the energy to adjust it to your needs.
Response to Bob Coleman
Bob,
You wrote, "It also helps if you have access to cheap water."
Perhaps that was a joke? The cost of water is irrelevant, since hydronic heating systems use closed loops. Once the boiler is filled with water, and the tubing has been installed, these systems don't (usually) need to be charged again with water.
or maybe...
he was referring to water based heat pump ??
The only high efficient setting other than mini splits
( again the complexity and setup cost is to be debated and taken into account )
is to use a water reservoir such as a large lake, as an energy dumper
still need to setup ventilation and heat exchanger + pumps ...
I vote for minisplits!
I have been impressed with minisplits for some time, but mainly as an "armchair quarterback" until recently. I believe they can be a very effective source for heating and cooling, if the space is very tight and well insulated. [email protected] http://www.greendsignbuild.net
But I had not installed one until this last year, (2013), when I installed one in a walkout basement living space in my basement. While until then, the space remained at close to 60 degrees in winter, in order to make the approximately 650 square feet of living space, I was closing it off from the heat source, the small boiler. So, in order to make the space consistently comfortable, I installed a Mitsubishi 9,000 btu, 21 SEER minisplit to provide heat, and (unneeded, as it is in the basement, cooling). However, it is now used to keep the humidity level at acceptable levels, even though it is not needed for cooling per se.
This space, as well as the entire extensively remodeled house is very tight, and very well insulated. While I have not done anything with the basement slab to insulate it, as that would have involved more than I was willing to do, the rest of the house is very tight and well insulated. The basement wall effective R value is about R20, until it reaches ground level, when it is about R35. The main house wall effective R value continues at about R35, and roof R value is about R60-65. The windows are nothing special, just Andersen lowE casements. If I had it to do over again, it would be interesting to use some of the now available much higher performance windows. But more than that, the house is extremely air tight. I also use a 200 cfm (on high) HRV, but it runs on low all the time except when it is bumped up temporarily with bath use. The total square footage for both levels of the ranch home with full basement is 2600 square feet. I use one 250 gallon tank of oil to heat and provide hot water for 4 adults for the entire year for the entire space.
The resident of the walkout living space likes to keep the space quite warm, so I needed to have a reliable means to keep it that way. I have been very pleased with the result. This past winter here in Maine, we had a number of below zero days, and the resident was very pleased with its performance, as they never had any time when they were anything but very comfortable. And after keeping a very close watch on the electric bill, I also am very pleased, as the total added cost of electricity never hit $20 a month.
Needless to say, I am now more than an "armchair quarterback" when it comes to minisplits! I am now considering installing an additional Mitsubishi 9,000 btu minisplit upstairs to provide cooling and supplemental heating, especially during the swing portion of the year, for the main level of the house. At present, we use an 8,000 btu window AC unit, that cools the entire 1300 square feet of the main floor. And that has its impact on our electric bill, even with an Energy Star 10.8 EER unit. But this time, I will go for the new, 30.5 SEER minisplit unit. I had meant to have the then available 26 SEER unit for downstairs, but only discovered the wrongly provided 21 SEER unit after I had already started installing it. It will be interesting to see what difference the 30.5 unit will make on the cooling bill. But perhaps even more so, I am interested in seeing what effect it will have on the heating bill, both in terms of the oil use, and the electrical use.
Back to aesthetics
A quick glance at the photo reveals plenty of other visible technology. Why is the minisplit different?
Response to Robert Swinburne
Robert,
I agree. One hundred years ago, kitchen ranges did not include hoods with exhaust fans. How many kitchen designers freaked out when exhaust hoods were first introduced? I have no idea -- but genuinely useful technical advances are usually accepted eventually, even if they look odd to some people at first.
I am going through this
I am going through this process currently on two projects -- one is a complete rebuild after a fire and the another is an upgrade (insulation/HVAC) of a house I originally remodeled in the early 90's - Just had an energy audit. I have an art cool in the house needing upgrades .. so I am not unfamiliar with the benefits of mini splits. What is surprising: The lack of information available from the manufacturers and the inability to find competent contractors ... not any change from 2006 when the art cool was installed.
Most people, myself included, are not going to install a bunch of the ugly wall heads throughout a traditional home ... the manufactures need to improve the concealed and ducted units for these to be commonplace in new builds and major renovations. They are fine in sunrooms and some kitchens -- great room at the shore .. but not going into my Pennsylvania farmhouse.
I would love to be able to find a contractor to install a Mitsubishi VRF unit and use conventional ducts in some locations and other single ducted units and then the wall units where suitable. This would be a solution for both houses.
One problem with the wall units is the need to run refrigerant lines and drain lines throughout the interior walls ... in many homes this is not advisable. And what happens in 10-15 years when you have to rip it out?
Mini-split Longevity
Does anybody have any info on maintenance issues for mini-splits.? In terms of specs, operating costs, etc., what's not to like? (Well, air distribution seems to be a bit of an issue.)
I just haven't seen any discussions of maintenance. Refrigerators seem like a comparable system- they're mildly reliable, but modern (read computer controlled, high-efficiency) ones have a reputation for failing regularly, although you don't hear much about the actual failure mode.
Hide with Art Placement and Wood Valence
Our minisplit will be placed on a rather visible wall. My wife, who's a watercolor artist, suggested a trick that "hides" the minisplit head by arranging art along geometric lines around it, so it doesn't disappear as much as become part of the whole (in our case including the horizontal and vertical lines from nearby windows and the television).
In addition, we'll build out a wood valence only across the middle of the minisplit where there are no vents to block, leaving the top and bottom completely open. That will help diminish the plastic color.
I've attached our mockup. I'll try to remember to post the actual results once we're done with our build.
Air Handler Height
First time poster here. Thank you for an excellent resource. This article suggests a solution to a problem I'm trying to address related to heating/and cooling a large finished attic in a 1920s foursquare with a typical hip roof and four dormers. I'm considering a mini split system. The problem is this: the room's dormers, kneewalls & cathedral ceilings come together such that there is no vertical wall space above about five feet high.
For several reasons I would prefer a wall-mounted air handler, however much of my research has indicated that I cannot mount the air handler below 6 feet off of the floor. Mr. Gibson reports that "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."
If I understand this correctly, my problem is easily solved. Can anyone share their experience with a lower-than-typical wall mount for a regular old air handler? Does anyone have any insight into why--in my own research--I keep reading about six foot minimums?
Again, thanks for a great resource.
Floor mounts...
The floor-mounted units work fine. In areas with kneewall spaces you can use mini-duct cassettes.
In a cooling environment you would ideally want the air intake for the unit to be near the ceiling to deal with stratification issues, but if it's for space heating it hardly matters. The air intake for wall-coil types is at the top of the head, with the exit air out the front, usually directed somewhat downward, but warm feet are more important than a warm head during the heating season, while a cool head is more important than cool feet during the cooling season. If you're using the same unit for both there is no perfect height.
Floor mounts...
Thank you for the info Dana. We'll be using the same unit for cooling and heating. Maybe I should look a little more closely at the floor mounted units, but so far (except for the short vertical walls) the wall mount looks like a better fit for my application. So what I need to determine is: given that I don't have any 6+ foot vertical walls, will overall wall mount unit performance suffer if mounted at roughly 4.5 feet. If the slightly lower wall mount doesn't impair unit performance in some way I currently don't understand, it sounds like cooling will be improved by maximizing any height I can work into the install, and therefore the wall mount @ 4.5 feet might be my best option (cooling is definitely the bigger challenge in this space).
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