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Urban Rustic: Choosing and Installing a Ductless Minisplit

A right-sized system and three indoor heads spells comfort, even when a polar vortex blasts into town

The Mitsubishi ductless minisplit includes an outdoor compressor and three indoor distribution heads. To date, the system has lived up to expectations. [All photos by Eric Whetzel]

Editor’s note: This post is one of a series by Eric Whetzel about the design and construction of his house in Palatine, Illinois, a suburb of Chicago. A list of Eric’s previous posts appears below. For more details, see Eric’s blog, Kimchi & Kraut.

 

The plan for our house was to combine an HRV or an ERV (for a continuous supply of fresh air) with a ductless minisplit air-source heat pump system for our ventilation, heating, and air conditioning needs. Almost all of the projects I had read about utilized this same combination, especially here in the U.S.

The only real debate, apart from specific brand options, was whether to use a single distribution head on our main floor, as opposed to installing multiple heads for a more dialed-in level of comfort (e.g., in the basement or the bedrooms).

Suggested equipment was grossly oversized

Our original builder had called for one head in the kitchen/family room and one in the basement, which was pretty standard for a Passive House level project. It was, therefore, pretty shocking to find that our second builder (there were two partners) and their HVAC subcontractor were suggesting a system that was grossly oversized for our needs. You can read about the details here.

This was just one of many red flags that convinced us to move on and GC the project ourselves. It’s also a reminder that old habits die hard, meaning that even seasoned contractors, in any trade, need to be willing to learn new ideas and techniques if they want to truly be considered professionals and craftsmen.

One of the disappointments associated with our build is, in fact, the disinterest (in some cases even outright hectoring contempt) shown by various tradespeople in our area for green building generally. Doubtless, at least a partial explanation for why much of the Midwest seems so far behind in adopting green building techniques, especially when it comes to air sealing, insulation, and indoor air quality beyond code minimum standards. Hopefully this changes significantly in the coming years.

Right sizing starts with a Manual J calculation

Consequently, I took Steve Knapp’s advice (from the comments section of my Q&A post on GBA) and contacted Home Energy Partners (their new name is HVAC Design Pros). Isaac responded quickly and eventually did our Manual J, confirming that we needed a much smaller system, one that is more consistent with a Passive House project.

Once we were on our own, in addition to going with a Zehnder ERV and a Mitsubishi ductless minisplit air-source heat pump system, we also pursued the possibility of using a Sanden heat-pump water heater. After seeing it used on a Hammer and Hand project, we thought it was a really interesting piece of cutting-edge technology.

Unfortunately, after getting a quote from Greg of Sutor Heating and Cooling, and a poor response from Sanden on questions we had about the system (they were unresponsive to emails), we decided to stick with our Zehnder, the Mitsubishi heat pump, and go with a Rheem heat-pump water heater. (Going with the Rheem saved us just over $6,000 in initial cost.) Hopefully, as it becomes more popular in the U.S., the Sanden can come down significantly in price, or maybe less expensive copycat products will someday show up on the market.

Greg was initially willing to work with us, even though we were technically out of his service area. He was nothing but professional, taking the time to answer any number of technical questions and offering what proved to be sage advice regarding various details for our system. But because we were installing only the minisplit and not the Sanden, he suggested we find an installer closer to us.

Finding our installer

We were lucky to find Mike from Compass Heating and Air. He came out to the job site and we walked through the details together. He proved to be knowledgeable, helpful, detail-oriented, and extremely professional. Installing our Mitsubishi ductless minisplit system with Mike proved to be one of the easiest portions of our build. We never felt like we had to look over his shoulder, making sure he got details right, or that we had to constantly confirm that he did what he said he was going to do — in fact, it was the opposite: Mike’s on site, so that’s one less thing I have to worry about.

Mike also confirmed what Greg and Isaac also pointed out: comfort issues may develop if we tried to get by with just one distribution head on the main floor.

In fact, looking back through old emails, Greg was nice enough to walk me through some of the options employed by those trying to get by with a single head for an entire floor (sometimes even two floors), including leaving bedroom doors open throughout the day (ideally, even at night), and even the use of Tjernlund room-to-room ventilators.

Again, to his credit, Greg tried to stress how important it was that homeowners have realistic expectations regarding the overall effectiveness of these techniques and options.

He also was at pains to make clear how the work of any competent HVAC installer can be easily undermined by a structure that underperforms. In other words, they can design an appropriately sized HVAC system for a Passive House, but if shortcuts occur during the build and the final blower door number comes in higher than expected, or the budget for insulation gets cut, reducing R-values in the structure, then the system they designed has little chance of working as intended. Based on what he wrote, I’m guessing he has dealt with exactly this outcome in the real world — not fun for him, or the homeowners to be sure.

By the time Mike got involved, we had pretty much decided to use multiple heads. In the end, we decided to delete the head in the basement, instead going with three separate heads on the main floor — the largest in the kitchen/family room, and the other two in our bedrooms.

Here are the specs for our system:

  • Hyper-Heat Compressor (30,000 Btu).
  • MSZ-FH15NA  (kitchen/family room).
  • MSZ-FH06NA  (master bedroom).
  • MSZ-FH06NA  (2nd BR).

 

This is the Mitsubishi head in the master bedroom. The Zehnder supply is to the right. Both are covered to protect them from construction debris.

Living with a ductless minisplit

Having lived with the HVAC system, both the heat pump and ERV, for about a year now, our only real complaint is summer humidity, which I discussed in a previous post.

This summer we’re going to try using a dedicated whole-house dehumidifier, which we think should resolve the issue. Otherwise, our system has been trouble-free.

In winter, the heads do make some noise, tending to crack or pop, especially when first turning on, or when they come out of defrost mode. Although I’ve read complaints about this online, it’s never really bothered us. I remember how loud our conventional gas-fired furnace was in our last house, especially when it first turned on, so I think it’s important to remember the level of certain sounds in their appropriate context.

Also, this crack or pop sound is, I suspect, louder than it otherwise would be in, say, a conventionally built home. Passive Houses are known to be significantly quieter because of all the air sealing and, in particular, all of the insulation surrounding the structure.

There’s also a noticeable humming sound when the compressor is going through a defrost cycle (especially noticeable at night when the house is otherwise quiet). The heads also temporarily send out cooler air during this defrost cycle, but the cycle is short enough that it hasn’t posed any real comfort issue for us.

In other words, having blocked out, or at least muffled, most of the noise from outdoors (due to extensive air sealing and extensive insulation), any noise indoors becomes much more noticeable and pronounced. The Rockwool we installed between bedrooms-bathrooms, and the kitchen-utility room for sound attenuation definitely helps in this regard (more on this in a later post).

Just how quiet is a Passive House? Well, one example would be the train tracks that are just a couple of blocks away: When the windows are closed the noise from a passing train is mostly canceled out — as opposed to when the windows are open, and the train, in contrast, sounds like it’s thundering through our next door neighbor’s yard.

Performance at very low temperatures

As far as extreme cold outdoor temperatures are concerned, the system experienced a real test with our recent Polar Vortex weather. Mike was nice enough to check in with us the day before it started just to remind me that the system could shut down if temperatures fell below -18° F, which is what our local weather forecast was predicting.

In fact, this proved entirely accurate. As temperatures eventually fell to -24°F overnight, the system was, in fact, off for a few hours (the Mitsubishi shuts off to protect itself).

With the Zehnder ERV already set to low, and using just a couple of small space heaters (one in each bedroom — roughly equivalent to running two hair dryers simultaneously), it was easy to get the interior temperatures back up to 68-70°F in less than an hour (from a measured low of 61° F when we first woke up), at which point we turned off the space heaters.

And it was just under two hours before the temperatures rose enough outdoors for the heat pump to turn back on. On the second day, the system again turned off, but the interruption was even shorter this time, so we didn’t even bother to turn on the space heaters.

On both days the sun was shining, which definitely helped as light poured in through our south-facing windows, mainly in the kitchen and family room. Even with no additional heat, either from the heat pump or the two small space heaters, the kitchen remained a comfortable 70°F throughout that first day, regardless of the temperature outside.

In the summer, when we have the AC running, we just set the desired temperature on the remotes and largely forget about the system. The three heads together, even in each individual space, have no problem keeping the house and individual rooms cool enough. In this case, it no doubt helps that we have a substantial overhang on the southern portion of our roof, mostly denying the sun an entry point into the home during the hottest days of the year (and the Suntuitive glass on our west-facing windows takes care of afternoon summer sun).

Single or multiple heads?

As far as using a single head to try to heat and cool the entire first floor, in our case about 1500 sq. ft., I can only say that I’m glad we chose to use multiple heads. This really hit home as I was completing interior finishes. For instance, there were times when only the head in the family room/kitchen area was running. When you walked into the bedrooms you could definitely feel the temperature difference since those heads had been turned off (roughly a 5-10° difference). As Greg, Isaac, and Mike — to their credit — were all quick to point out, for some homeowners this temperature swing would be acceptable, even something that could be calmly ignored, while for other homeowners it might well be a heartbreaking and deeply frustrating realization.

Depending on how sensitive someone is to these temperature differences, it could  prove a devastating disappointment if the homeowner is expecting uniform consistency throughout their home. Also, since much of the selling point of Passive House techniques is, in the end, occupant comfort, and not just reduced energy consumption, moving from a comfortable kitchen, for example, to a bedroom that some would find outright chilly, might induce some homeowners to wonder what the point was of all that air sealing and insulating.

Obviously it’s only our opinion, but if it’s at all possible to fit it into the budget, by all means utilize more than one distribution head. Even if you yourself never feel compelled to turn on any of the other heads in a multi-zone system, a spouse, one of your kids, or a guest probably will want to have the option at some point.

 

The compressor with finished charred siding and decorative gravel-cobblestone border.

The one real risk we took with our HVAC set-up was foregoing any direct conditioning in the basement, either heat or AC. In the summer, no matter how high the temperatures outdoors, the basement stays within 5 degrees of the upstairs temperatures and humidity, so no comfort issues in this regard have presented themselves. In the winter, however, the temperature remains in the 59-61° range, with almost identical humidity readings as the main floor.

Mitsubishi wall-mounted heads: beauty or beast?

I’ve read that some interior designers, and even some homeowners, have expressed aesthetic concerns about the distribution heads. If you go on design-oriented websites like Houzz you can come across some really strong negative opinions on the topic.

For us, they’ve never been a problem. Much like the Suntuitive glass on our west-facing windows, or even a dark or bright color on an interior accent wall, after a few days, like anything else, you just get used to it. I never found them to be ugly in the first place though.

The appearance of the ductless minisplit distribution heads have never been an issue.

I also grew up with hydronic metal baseboards for heat, while in apartments and our first home we had the typical floor supply and wall return grilles for a gas furnace. Point being, the details of any HVAC system are never completely absent from any living space. There’s always something that shows up visually and, typically, that needs to be cleaned at some point.

In addition, the Zehnder ERV and the Mitsubishi heat pumps meant we didn’t have to use any framed soffits or duct chases (at least in the case of our specific floor plan) in order to hide bulky runs of traditional metal ductwork, typical in most homes when using a normal furnace. Unless designed with great care, these tend to be obtrusive, taking up premium ceiling, wall, or floor space. And if randomly placed simply for the convenience of the HVAC contractor, they can be downright ugly.

In other words, it doesn’t really matter if you’re building conventionally or if you’re building a Passive House, all the details of an HVAC system — whether it’s individual components, or even how these components will be placed inside a structure — should be carefully thought through (again, ideally before construction begins) to address any performance or aesthetic concerns.

Operation and maintenance

As far as the remote controls for the individual heads, we haven’t had any issues.

For the most part, we set them to either heat or AC (roughly 70° and 74° respectively), and then forget about them. And when the weather is pleasant outdoors, we take every opportunity to turn off the system completely and open windows.

The system could be combined with a Kumo cloud set-up, but we’ve been happy with the hand-held remotes so far.

I try to check the filters for the individual heads at least once a month (more like once a week when I was still doing interior finishes). Just as it takes much longer for the Zehnder filters to get dirty now that construction is over, and the same has proven true for the blue filters in the Mitsubishi heads. It seems like about once a month is sufficient to keep up with the dust in the house.

Overall, we’ve been very happy with our HVAC set-up, including the Zehnder ERV and our Mitsubishi ductless minisplit. As long as the units don’t have any durability issues, we should be happy with these systems for many years to come.

 

Other posts by Eric Whetzel:

32 Comments

  1. Lance Peters | | #1

    Thanks for another great read, Eric. Can you remind us about the details for your build, like the size of your house and the heat load and design temp etc. for the main floor? I'm always curious about these things, it helps put the equipment performance into perspective.

    Have you any feedback on your energy bills vs what your modeling predictions were?

    Regarding your unheated basement, was there any discussion with your HVAC contractor regarding the heating load on the main floor being reduced by adding heat to the basement? I'm curious how much overall savings there are by not heating a basement.

    1. User avater
      Eric Whetzel | | #18

      Thanks Lance!

      The house is single story, roughly 1500 sq. ft., oriented east-west along its longest axis (family rm and kitchen to the south, bedrooms and baths to the north). We followed Passive House principles, although we never intended to pursue official certification, so we consider the house to be a mix of Passive House and Pretty Good House.

      I'll attach the load report Isaac did for us, which should answer some of your system-related questions. It might also help someone who's never seen one. It also includes diagrams of our floor plan, both for the main level and the basement (last 2 pages).

      Even with having to use 2 dehumidifiers last summer, along with me spending most of 2018 finishing the interior --- so using a significant amount of electricity for power tools (wood flooring, tile, kitchen cabinets, shelving, and wood trim) --- we still came in under the max. overall energy use allowed by Passive House. Nevertheless, it was more than we were expecting. I'll do a future blog post going over the details.

      The extent to which we needed the dehumidifiers was a shock, so we've concluded it's just an unavoidable necessity in a Passive House, or high-performance build, at least in areas of the country that see even short periods of high humidity. We had them running pretty consistently May-September.

      I think we assumed having a distribution head in the basement would lessen the load on the main head in the family rm/kitchen, but concrete numbers were never discussed.

  2. Russell Miller | | #2

    I see design pros isn't doing any hvac design at present. Just an FYI to other readers.

  3. Jon R | | #3

    I'm curious - in the first photo, how was the Zip air sealed to the foundation?

    Some good lessons. Backup heat is important (preferably permanently installed and automatic). Bedrooms need an efficient heat source. Dehumidification is important.

    > (the Mitsubishi shuts off to protect itself).

    Which makes me wonder that happens with other brands that don't shut themselves off when operated below their specified minimum temperature. Increased wear?

    1. User avater
      Dana Dorsett | | #5

      >"Which makes me wonder that happens with other brands that don't shut themselves off when operated below their specified minimum temperature. Increased wear?"

      With Mitsubishi I believe it's about their outdoor temperature sensing thermistor going outside the range of their control algorithms, not excessive wear. Other control approaches or sensors aren't going to have identical issues. The -18°F temperature at which Mitsubishi

      specifies as the warmest temperature it might turn off is itself below the specified -13°F to 75°F operating range, yet they separately specify that that the Heating Thermal Lock-out / Re-start Temperature will be within -14°F to -18°F. They clearly expect it to be operating at -18F, even though that's "...below their specified minimum".

      The specified heating operating range of a Fujitsu xxRLS3 is -5°F to 75°F, whereas the specified range for the IDENTICAL (except for pan heater) xxRLS3H is -15°F to 75°F.

      I don't believe any vendors void the warranty for operating the equipment below the specified minimum temp, but Mitsubishi (and probably Fujitsu) won't warranty against pan-ice damage on units not equipped with a pan heater.

      1. Jon R | | #6

        I agree that -18F is likely to be safe enough. Below that and who knows.

        > I believe it's about their outdoor temperature sensing thermistor going outside the range

        Having worked with thermistors, I know that such an issue would be trivial to fix (and would be much more convenient for cold climate customers). So I find the explanation unlikely (ie, the reason is serious/important and not trivially fixed).

        1. User avater
          Dana Dorsett | | #7

          >"Having worked with thermistors, I know that such an issue would be trivial to fix (and would be much more convenient for cold climate customers). So I find the explanation unlikely (ie, the reason is serious/important and not trivially fixed)."

          ... and yet the verbiage next to the the double-asterisk in the Mitsubishi documentation reads:

          " **System cuts out in heating mode to avoid thermistor error and automatically restarts at these temperatures. "

          Having designed precision temperature controls over multiple and wide temperature ranges, I too believe this would be dead easy to fix in a design revision. But it's been this way for over a decade, starting with the original FE series cold climate mini-splits (or maybe earlier.) Since the vast majority of the equipment is installed in locations where it doesn't drop below -18F on a regular basis they probably don't get enough complaints about it to bother fixing it.

          Forward / backward compatibility issues among sub assemblies/components may be why it persists (just a guess), but that feature IS a reason I would personally avoid using or recommend Mitsubishi in US climate zone 7 locations or colder.

          1. Jon R | | #8

            > documentation reads ...

            And other models just happen to experience "thermistor error" at higher temperatures (-9F).

            Mitsubishi also writes "Many ductless systems were actually designed to shut down at -10º F in order to protect the technology from failure." Sounds to me like there was (and probably still is) some link between very cold temperatures and a serious problem. The marketing department may see no benefit in elaborating.

            I wouldn't use a Mitsubishi without backup even in some zone 5 areas.

          2. Lance Peters | | #9

            Maintaining operation as the mercury drops and starting up cold soaked are two completely different things from an equipment design perspective. That may have something to do with the choice of temperature.

            Also consider that all mini-split manufacturers shut their systems down at relatively similar temperatures. Perhaps R410A compatible lubricants have low temperature limitations? Just a guess.

          3. Lance Peters | | #10

            On that note, why have we not seen mini-splits with built-in electric back up heat? I have a feeling that integrating electric back up heat would be a game changer for the mini-split market.

    2. User avater
      Eric Whetzel | | #19

      Hi Jon, you can read about the details, with photos, here:

      https://kimchiandkraut.net/2017/01/25/framing/

      Let me know if you have any questions.

  4. Doug McEvers | | #4

    Eric; From the photos the workmanship looks to be excellent, something not often seen. If you have not already how about performance numbers for the house?

    1. User avater
      Eric Whetzel | | #20

      Hi Doug,

      We ended up at 0.20 [email protected] and 106 [email protected] for our final blower door test. We also came in under the PH requirement for overall energy use (2018), no doubt aided by the air sealing, extensive insulation, the use of all LED light fixtures, and Energy Star appliances --- not to mention badgering my wife and daughter to turn off lights when they leave a room (I've officially turned into my dad).

      How much of our energy use is directly attributable to HVAC, including the ERV, we don't currently know, although we may try and monitor it in the future.

  5. User avater
    raul4817 | | #11

    Eric,
    Thanks for sharing. Its exciting to read real results from a build so close to me. I am also in the Chicago burbs(north riverside). I have decided to move forward with a fujitsu mini with some very knowledgeable insight from Dana. Its comforting to hear that your mini made it through relatively unscathed from this winter's polar vortex. I share your concern with how far behind our city and region is in regards to green building. I find that a good portion of contractors and homeowners around my parts put very little emphasis on efficiency and performance.
    Raul

    1. User avater
      Eric Whetzel | | #21

      Hi Raul,

      Unfortunately, we're still considered freaks by most people in the Chicago area. :)

      For example:

      My city outsourced the plan review, worried about possible liability (although they were very easy to work with throughout the build, apart from one inspector), at least in regards to Passive House details.

      I really struggled to find a siding company willing to take on all the details for the insulation, furring strips, and cedar siding. Most siding companies around here mostly install fiber cement directly over Tyvek. I had many contractors out to the site who expressed interest, but only one was willing to give me a number --- the others, I think, were terrified of losing money since many of the details were so new to them. It also didn't help that as a homeowner I was acting as GC.

      And I still have current and former clients of my original builder contacting me about how awful it is to work with him. People are still going with him because so few GC's seem interested in "green" building in our area and people don't know who to ask for help.

      It's a real shame since homes in the Chicago area could really benefit from proper air sealing, significant insulation, and proper ventilation, especially with our weather extremes.

      Feel free to email me directly if you're still looking for any subcontractors, or if you have questions about anything. I'd be glad to help if I can:

      zewt [at] hotmail [dot] com.

      Good luck with your project!

  6. Malcolm Taylor | | #12

    Eric,

    Great blog.

    A question for you: I've got a client who wants me to put Shou-shugi-ban siding on their place. How easy is it to treat cuts and butt ends when installing? How do you re-touch it?

    1. John Clark | | #13

      "For cut ends and mitered joints, we will use tung oil to help seal these areas (similar to painted wood siding that gets a swipe of oil based primer in these same spots just before installation)."

      https://www.greenbuildingadvisor.com/article/urban-rustic-the-cedar-siding-is-here-lets-burn-it

      https://www.terramai.com/blog/faux-sugi-ban-charred-wood/

      There's a NY TIMES link embedded in the article which suggests that this technique really only works with Japanese Cedar. *shrug*

      1. Malcolm Taylor | | #14

        John,

        I'm more worried about the uniformity of the look. Tung oil might protect the cut, but it is going to be a lot different colour than the charred areas.

        I'm also curious about:
        - Cleaning the siding. I presume you can't take a power washer to it if a seagull flies by.
        - Caulking the charred siding at penetrations etc.

        1. John Clark | | #16

          Uniformity? What about rustic charm? Isn't that more important? (lol)

          IMO the suggestion that domestic (North American) wood varieties are ill-suited to using this technique is enough to scare me off.

          This may help:

          https://nakamotoforestry.com/wp-content/uploads/2018/03/Nakamoto-Forestry-Maintenance-Spec.pdf

          https://nakamotoforestry.com/wp-content/uploads/2018/03/Nakamoto-Forestry-Installation-Spec.pdf

    2. User avater
      Eric Whetzel | | #22

      Hi Malcolm,

      I had the siding guys use a plumber's torch to burn any cut ends before installation. Since I didn't ask them to oil these areas before installation, it turned out to be a pretty good experiment, testing the impact the tung oil has on retaining the char. The answer, at least in our experience, is a lot. Any areas that were burned but not oiled lost almost all of their char in the first year.

      Since trying to re-burn the cedar once it's installed would be unwise, I used a Scandinavian pine tar finish to do touch-ups. I learned about it from another GBA blogger:

      https://blueheronhaus.com/tag/black-house/

      It worked really well, blending with the existing char while making these edges an opaque black.

      In fact, my wife and I are still debating how much touch-up is necessary on the face of various boards. I like the aged look that some exposure gives, while she prefers a more consistent, monolithic black. I'm guessing we'll compromise by having me touch-up only the most obvious and worst areas.

      Thankfully, there aren't that many areas worth arguing about. Nevertheless, we probably lost about 20% of the initial char in the first year. By the end of this summer I should know if that process is mostly over, or if it's only going to get worse.

      There was a project featured on the British TV show Grand Designs that used shou-sugi-ban and almost all of the char was gone after the first couple of years, but I don't think they used any kind of oil finish on the wood before installing. The house was also sited near a body of water that saw a lot of wind and rain, so I'm sure that played a part as well.

      I'll go through the siding details in an upcoming blog, but just as an FYI, in regards to insects, we did have some carpenter bees last summer, although they initially nested in the exposed sub-fascia before siding went up. Had I understood their lifecycle, I would have addressed these spots before siding went up --- I thought just closing these openings off with some caulk would work.

      We've also had one visit from a woodpecker, although he hasn't returned. I'm hoping because he didn't find any insects that he won't come back, but only time will tell.

      Worth considering if there's a lot of carpenter bees or woodpeckers near your client's project.

      Feel free to email me directly if you have more questions:

      zewt [at] hotmail [com]

      I'd be glad to help if I can.

      Even though we've had some issues with the charred cedar, I still love the look.

      And it does tend to confuse people since it has an aged patina even when brand new: "So is this a new house, or an old one?"

      1. Malcolm Taylor | | #24

        Thanks Eric - that's extremely valuable for me.

        I'm not sure it is a long term fit for these clients. Their primary interest is in having a black house, which has been very popular on architecture sites for the last couple of years. The added complexity of working with it over the alternative (Hardi Panels detailed as board & batten), the reluctance of the siding contractor, and time constraints probably mean we will pass on this job.

  7. Len Moskowitz | | #15

    We built a PHIUS-certified Passive House in northern NJ. 1100 ft2 per level, roughly 4,000 ft2 total. It was completed in 2014.

    You can read about it's early beginnings here:

    https://www.greenbuildingadvisor.com/article/passivhaus-building-the-modular-way

    The house has two Mitsubishi 12 kBTU Mitsubishi Hyper-heat ductless mini-splits. One is on the main floor and the other is on the second floor. The third floor and basement don't have heating or AC.

    The two mini-splits produced heat even when the outside temperature was -10 degrees (F).

    We also have a Zehnder ERV for the entire house.

    As long as we leave the doors open to the third floor, it stays within two degrees of the first floor. The basement stays within roughly three degrees of the main floor.

    If we close doors, the third floor drops to four or five degrees below the main floor. The basement drops to five or six degrees below.

    The guest bedroom in the back of the main floor will get a bit cool if its door is closed. We have a quiet, low capacity electric resistance heater in there. It gets used once or twice a year.

    For most of the heating year, the main floor unit is adequate for the whole house. In the dead of Winter, we add the second floor unit, mainly for distribution rather than capacity.

    We had a durability issue with the main floor unit's heat exchanger. After two years it sprung a leak and had to be replaced. While the warranty covered the replacement part, the labor cost us pretty much as much as a new one.

    Our total energy usage for the year (HVAC, lighting, cooking, computers, media, car charging) has been under $1000. This year, with time-of-day metering, we expect it will be under $500.

    Oh - we have a 9.6 kWh solar array on our roof.

    If you're on Facebook, you can learn more about our home in the "Passive House NJ" group.

  8. Josh Durston | | #17

    I'm curious what made you go with the MXZ-3C30NAHZ instead of the MXZ-3C24?

    1. User avater
      Eric Whetzel | | #23

      Going slightly larger, in terms of capacity, gave us some insurance in case the energy modeling was off, or if actual usage (occupant behavior) was higher than expected.

  9. User avater
    Dana Dorsett | | #25

    The FH06 are good for 8700 BTU/hr when married to a big enough MXZ compressor, and the FH15 is good for 18,000 BTU/hr, so combined there is enough head capacity for 35,500 BTU/hr.

    http://meus1.mylinkdrive.com/files/MSZ-FH06NA_For_MXZ_MULTI-ZONE_SYSTEMS_ProductDataSheet.pdf

    http://meus1.mylinkdrive.com/files/MSZ-FH15NA_For_MXZ_MULTI-ZONE_SYSTEMS_ProductDataSheet.pdf

    (With enough compressor that's enough to heat my sub-code 2400' antique house +1600' basement to 70F when it's 8F outside.) .

    The 3C24NAHZ is only good for 25,000 BTU/hr @ +5F, and less as the temps drop off.

    The 3C30NAHZ is good for 28,600 BTU/hr @ +5F, which STILLL isn't enough to drive the full potential output of all three heads to their maximum at the same time at +5F or colder.

    http://meus1.mylinkdrive.com/files/MXZ-3C24NAHZ2_ProductDataSheet.pdf

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

    Whether in the end this house was really running the 3C30 at it's maximum when it stopped running at -24F isn't known (maybe) , but it has the same minimum output as the 3C24, and any hit from the marginal oversizing isn't going to be much.

    Mind you, at -13F single zone FH06s are good for 6430 BTU/hr (12,860 for a pair), and a single zone FH15 would be good for 14,580 BTU/hr @ -13F for a total of 27,440. That's almost as much as what the 3C30NAHZ can muster at +5F, and the combined minimum modulation @ +47F of three separate mini-splits would be 8,350 BTU/hr, not much more than the minimum output of the -3C30NAHZ (and you could turn some of them completely off when it's that warm out.)

    http://meus1.mylinkdrive.com/files/MSZ-FH06NA_MUZ-FH06NA_ProductDataSheet.pdf

    http://meus1.mylinkdrive.com/files/MSZ-FH15NA_MUZ-FH15NA_Submittal.pdf

    Whether it's worth the "visual noise" of three compressors vs. one is a judgement call, but it's often cheaper and almost always more efficient than a multi-split running the same three heads.

  10. David Jones | | #26

    I realize that oversizing of HVAC equipment is generally a bad thing. With variable speed inverters on the mini splits, I have read that that oversizing may offer an efficiency advantage. The theory being that the larger unit operates at lower speed more hours per year. However, I also find that smaller individual units offer higher efficiency ratings that larger units. (Combining two smaller units may offer better efficiency than a single larger unit with multiple heads).

    1. Jon R | | #28

      People tend to get too worked up about sizing moderately more than Manual J (not guess) loads.

      "Oversized equipment doesn’t really carry an energy penalty or a comfort penalty anymore. (Newer modulating or two-speed furnaces operate efficiently under part-load conditions, solving any possible problems from furnace oversizing; and oversized air conditioners aren’t really as terrible at dehumidification as many energy experts claim.)"

      https://www.greenbuildingadvisor.com/article/when-do-i-need-to-perform-a-load-calculation

  11. David Jones | | #27

    Single point source vs. multiple units or heads is a judgment call. I built a zero energy cape with a single ductless unit. The owner did extensive temperature measurements and found a 3-4 degree temperature difference from the warmest room to the coolest. We viewed this as a success, but that project prioritized low cost. That house also had a circular air flow pattern on the first floor that made the single unit work well. Other floor plans would not lend themselves to a single point source. With a higher budget on an upcoming project, I plan to use two individual units (which have higher efficiency ratings than a single large unit). The two units will offer better distribution, "zoning", system redundancy, and higher efficiency.

  12. Ben Elliston | | #29

    High wall head units for mini splits are not the only option for those bothered by them. There are floor consoles and ceiling-mounted cassettes. My floor console sits about 8cm off the floor (so it clears the skirting board) and, although I didn't do so, it can be semi-recessed into the wall. It looks good and most people who see it have never seen one before!

  13. Robert Pinder | | #30

    I have a small mixed commercial/residential building with a total of 6 mini-splits here in southern Ontario. Two of the apts are heated AND cooled by them, the other four are used for cooling only. I purchased 7 Shinco 9K and 12Ks in 2011 - four have had to have been replaced so far! They SEEMED like a great deal then at around $500.00 US each.
    One of the apartments is long and narrow - 60' long and has two minis because of the length. These no- doubt will fail sometime in the not-too-distant future. My HVAC tech has suggested not to replace them with a single outside unit with two heads when they go. His argument is if there's a problem then both units will fail to operate - if I stick with two full units I will always have a back-up which will run.
    Any thoughts on his theory?

    1. User avater
      Dana Dorsett | | #32

      Most muli-splits require at least two functioning heads to operate. If one head is dead, there's a good chance that the other won't run. They also have a more limited turn-down range than single zone mini-splits.

      It's also usually/often more expensive to install a 2-zone multisplit than a pair of single zone units. A typical reason for going with a multi-zone version is insufficient space to install multiple outdoor units, which is clearly not the case here.

  14. David Jones | | #31

    Regarding finding a GC and other trades interested and knowledgeable about high performance/green building. As a GC myself, I share your frustration, but its not as impossible as you think. You aren't likely to find a GC like that through normal channels. Look for other other homes that have been built to the standard you seek and find those builders. Look at award programs for green homes. High performance builders exist but we find it just as difficult to find clients who want to build this way.

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