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Community and Q&A

Multiple Minisplits vs. Multizone System

Bernard Lam | Posted in Green Products and Materials on

To go ductless means a lot of miniplit heads. On top of that my local energy codes demand a minisplit system that is energy star certified. That is easy to find in single zone systems. But in multi zone, not so much. Ideally I’d like one of those 8-zone capable unit to serve a 4 bedroom house with an office. Even a 5 zone unit is a stretch. And for climate zone 5, I need a “hyperheat” model or equivalent.

One can get around this energy star requirement by installed 2 multi-zone units that are energy star certified, such as this L4L30A09090912. 2 of Them would provide 8 zones.

What I’m wondering is, is it better to do an 8-zone unit or 2x 4 zone units? How big of a difference should I expect for installation costs? what about overall energy use? I think the 8zones require branch boxes etc and is more complicated to install. And if they are significantly less efficient, then 2x 4 zone might be better?

Another possibility is to use in wall ducted heads and split the output into bedrooms that are next to each other. But again, I’m having difficulty finding ducted heads that are energy star compliant. It seems the standard wall mount units are always the most efficient and any other type of head is rarely energy star certified. Any recommendations on where to look?

Edit: I just saw a similar question posted in 2019:

Energy efficiency of multi zone mini splits vs. multiple single zone?

I’ll read through that but I’ll leave mine up for now hoping maybe there are newer models that may have come out since then that people might recommend me to research.

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  1. Paul Wiedefeld | | #1

    Is this an existing house or not?

    I wouldn’t let the rebates guide your thinking here. Multi-zone systems really struggle efficiency and comfort wise and should be a last resort. The ducted path is easiest and will fit the heat load much better.

  2. Kyle R | | #2

    Carrier 9k-24k ducted mini splits are “hyper heat” and Energy Star certified. Look at this link page 11.

    Ducted is definitely the way to go.

  3. Bernard Lam | | #3

    its a new build.

    Theres no way to avoid multi zone units for me, its a matter of 2x quad zones or 1 8-zone. There's limited opportunity for ducting, and even the concealed duct head units require a lot of space (i.e. framing a false ceiling) just to hide it. I might be at a push able to use 2 ducted heads to heat 4 bedrooms. In that case I'd still need a single 5 zone to heat the rest of the house.

    1. Paul Wiedefeld | | #4

      Is cooling a requirement?

      Is the heat loss complete? The bedrooms should have extremely low heat losses and will match terribly with a multi-split. If ducting isn't an option, look at more than 2 outdoor units. Air-to-water is also better for zoning, not sure if any of those are Energy Star rated.

  4. PBP1 | | #5

    Maybe fully explore scenarios where a multizone single ASHP makes sense over one-to-one units. I would have needed three one-to-one units, which is impractical considering the fact that a single somewhat undersized ASHP paired with three ducted air handlers is doing fine (zone 5), with minimal energy surcharge compared to three one-to-one units. I think three one-to-one units would have driven me crazy, the noise and ice formation with a single ASHP is enough, not to mention each one-to-one needs its own circuit.

    So, zone 5, 2100+ sq ft, design temp -1F, heat load 28k all OK with a single Mitsubishi Hyper-Heat rated at 28k (47F) paired with 15k, 12k and 9k heads. Thus, the total head capacity is 130% of the rated capacity of 28k. If min output is 35% of rated, then that's 9.8k, which feeds the 15k, 12k and 9k heads. Divide 9.8k by three zones and you have ~3.3k per zone. If it's cold (demand for heat), then 3.3k per zone is not excessive (i.e., 9.8k for entire house with largest space (15k zone) north facing with excessive fenestration).

    Of course, as people repeat time and again, a one-to-one non-ducted is the MOST efficient (if properly sized). There's absolutely no argument there. However, at some point, one-to-one hits the law of diminishing returns - and ducts can be quite useful for comfort, air movement, filtering, etc.

    1. Expert Member
      Akos | | #6

      The issue isn't with multi splits in general, the problem is with wildly oversized multi splits. In almost any home, when people are starting to look at these 6 to 8 zone setups, the oversize required to have the right number of zones means the system will never run efficiently.

      A correctly sized multi split with decently sized zones (ie no 6k heads on a 48k unit) will work just fine.

      1. PBP1 | | #9

        Thank you Expert Member ;-)

      2. Bernard Lam | | #10

        Would PBP1's strategy of under-sizing the outdoor units compared to the indoor units be effective, essentially creating 3k units for each bedroom which is closer to the heating loads of those relatively small rooms? like a 36k unit powering 7+7+7+7+18 where the 18 is for the open plan living room?

        Or maybe 2 multi splits, 1 undersized for bedrooms only, and the other properly sized for the common areas?

        Another consideration is, this Manual J was required by my local building permit, would they make me do the calcs and then let me undersize compared to what is shown anyway? seems unlikely.

        1. Expert Member
          Akos | | #11

          Couple of issues.

          The engineering documentation is not clear on how the capacity is shared between multi zone setups. There is some modulation on each head, but it does seem limited. Also since each zone might not be calling for heat at the same time, you could end up with a head running at full tilt, than shutting off right away. Not the best for efficiency or comfort.

          Wall mounts are not zero maintenance. They need periodic cleaning of coil and blower wheel, which is not a simple (or cheap) job, times that by 5 and you have indirectly purchased an expansive service contract. The drain line also seems to clog on them on regularly enough.

          They are also not without noise. When the unit cycles on and off, you get thermal expansion as the coil heats and cools that can create popping sounds. When the unit goes into defrost and refrigerant flow reverses it will make enough noise to wake you when you are sleeping.

          Even the smallest wallmounts also put out a fair bit of air flow, this can be uncomfortable in a bedroom during cooling season.

          I'm speaking from personal experience here, its been a couple of times that I've gotten very close to ripping the wallmount and multi split out and replacing it with a ducted unit.

          So in your case, you can go with a multi split but with some care. A single large wallmount for the living space could work and reduce ducting. Zone costs are around $5k, which would buy you a lot of ducting.... The rest of the smaller rooms in the house could be all connected to a single multi position air handler or if you want a bit more zoning, a pair of slim ducted units.

          Almost 1/2 of your heat loss is glazing. This is one of those cases where investing on some better windows (ie triple pane fixed units where operable is not needed) is a good thing.

          I didn't go into detail of your man J but if the 57k is correct, that is a very inefficient 3300sqft structure. I'm in slightly warmer climate, but that is only slightly better than the heat loss for uninsulated double brick structure here.

          1. Bernard Lam | | #13

            Sounds like you are not too fond of minisplits in general. The noise/vibrations/cleaning is a given if I'm to use minisplits? The thing is, its an all electric house, so its either resistive heating or some form of heatpump. The best config is what I'm trying to figure out here.

            I do get the concept of undersizing the outdoor unit, and think theres merit to it. If undersized sufficiently (30%?) and with one of the heads appropriately sized for the space. E.g. the 7k units in the bedrooms will reach setpoint temps easily, while the 18k unit serving the greatroom/dining/kitchen will need full power, then "one would expect" the bedroom units will get modulated to operate at minimum capacity while giving full power to the big unit. But you are right, thats just a guess. Sounds like no one will actually know. There must be alot of people with multisplits here who can give us an idea if their efficiency is significantly worse, or obviously disappointing. Real life application might end up showing its a wash anyway?

            But there are even more questions like, does an indoor head running full tilt with an undersized outdoor unit actually use less energy than if it was running intermittently with an appropriately sized outdoor unit?

            Also, the elephant in the room for me, is that most of the time I'll be in the "shoulder seasons" where there is little heating or cooling needed (thats the hope) so if these multisplits arent that good at modulating its output, then its pointless however you size it.

            The problem I see is that 1. they dont make smaller indoor units for bedrooms. Like 3k units. 2. The claim that multisplits are not effective at modulating its output to save energy, which is counter to what the marketing says. But who do we believe?

            I'll have to go back to my Beopt model to double check the heatload against this manual J

          2. Expert Member
            Akos | | #17


            I'm very fond of mini splits, I've gotten many installed over the years including around a dozen in rental units. They are great for retrofit application to add cooling to older homes.

            I've also installed a budget wall mount for my wife for heating/cooling an old garage that go converter into a studio, best decision ever. Compared to baseboard heat, it costs so little to run that don't even have to bother with setbacks.

            I've also have worked with them long enough to understand the limitations and their weaknesses, which is why I think a larger number of wall/ceiling/floor mounts are not a good idea for a new build. I would even say, a terrible idea.

            If you are building something small with PGH insulation levels and open concept layout, a single wall mount or a wall mount+ducted unit is a great way to condition it. That is not what you are building.

            Thinking more about the amount of glass in your place and your climate, I think a wall mount is actually a very bad idea. Even with triple pane windows, that much glazing it will be cold near the windows. For creature comfort, you need to provide heating near the windows, this means registers near the window or floor heat.

            As I said earlier, there is not a lot of hard engineering information on how exactly these operate. From posts on this forum, I can tell you putting something like a 3 zone multi with a smattering of 6k or 9k heads to heat bedrooms doesn't work well. COP tends to hover close to 1, some zones tend to overheat or overcool and there are major humidity removal issues with them.

            For example, my own older LG multi split, does not module the indoor heads at all. The heads are either on at rated output or off. This means in the bedroom you get a blast of super chill followed by a long period of no cooling and high humidity as the water on the coil re-evaporates.

            The outdoor unit does modulate and ramp to meet the demand from each zone, so maybe other units with decent controls can perform better. The efficiency of the setup is also not that great. I have power data for similar size building and my setup uses about 40% more energy than a one to one setup.

            Multi splits do have a modulation range, but it is usually around 3:1. A one to one might be be up to 10:1. This is fine if you have a couple of large zones connected to it. Once you add in a small zone, especially during shoulder season, you'll get into situations where the heat call is bellow the min capability of the outdoor unit which will mean that it needs to bypass refrigerant through the rest of the zones. This is pretty bad for efficiency and comfort as zones that are off can overheat.

            I would go through your building losses again and figure out what your actual heating load needs to be. If you are in this 5 ton range with a lot of glazing, I would look a setup with a couple of heat pumps with high pressure air handlers (ie Zuba or SkyAir).

            With a lot of glazing, there tends to be big heating/cooling differences based on time of day, you'll most likely need a fair bit of zoning. Make sure whichever equipment you select has decent zoning options. At 5 tons, even a geo setup might be worth it. Won't be cheap, but even full floor heat might not be a bad idea.

  5. Bernard Lam | | #7

    I've attached my manual J. If I understand this correctly on Page 15, it says I'll need 55727Btuh total heating capacity from my minisplit? So I should be looking at a 54k system? They do have a 5-zone at that size.

    1. PBP1 | | #8

      I see "heating equipment", "heating equipment summary" and "heating output" at 26615 BTUh (26.6kBTUh) (page 13 and page 43).

      I have taken a look and see that the location is at about 5000 ft and not so far north, with a design temperature of 7 F (dry bulb, db). As to insulation, walls 27, floors 30 and ceiling 59 and windows all below U 0.3 (many around 0.24). My house is pretty close to the same in terms of insulation and windows (ceiling is less) though I have a design temperature of -1 F db and I'm in MT, at least 600 miles north (I also lived in ABQ). If I multiply my -1 F load of 28K by 1.52 (difference in sq ft or volume), I get about 43 kBTUh and again that's at -1 F design temp not your warmer +7 F and for a location 600 miles north hence less sunlight. If adjusted for such factors, that estimated load number would be less. On a sunny day like today (or yesterday) with outside temp in the 20s F, my south facing garage door (grey) is over 100F (again, 600 miles north). Maybe check out your glazing load?

      Are you sure the 26.6 kBTUh is not the equipment recommendation?

      From NREL:

  6. Kyle R | | #12

    It looks like you have 1,200 sqft of glazing? Are your window u values properly entered to the software? If they are, I would consider substituting the external insulation you have planned and get some triple pane windows.

    1. Bernard Lam | | #39

      I went back and re-ran my Beopt energy model with U0.17 triple pane windows, the most insulated option I can pick in the program. An $80-150k upgrade depending on who you go with. Results were pretty clear.

      I used "auto sizing" in the model for my HVAC capacities and it gave me 53kBtuh for heating with the current, as built, dual pane U0.27 windows. Which agrees with my Manual J.

      With triple pane windows, the model suggested 43kBtuh, about 20% decrease in HVAC equipment capacity .

      For site energy in kwh/year, its 23798 vs 22969, savings of 823kwh/year, thats $75 per year. Does that even sound right? Or triple glazing really does that little?

      Double check: The model shows just less than 6000kwh/year in heating with heatpumps. Thats about $600 - sounds about right.

      Of course, everything rests on the 25kw PV this house was designed around, 32000kwh/year estimated production. I did a single slope shed roof facing south for this reason, in hopes that I can get the tesla roof. When I got a quote with sunrun through costco, it was around $80k of panels for that size, but thats the cost on top of a new roof. Tesla solar roof can do it at the same 80k but that includes the roof. Either way, I remember reading multiple articles on here that more PV is always more effective than triple pane windows, and my energy model seems to strongly agree. Of course that assumes one has the space for more PV.

      BTW with the cost of metal these days, my roof in standing seam would be $60k. I should also point out that my tesla roof pricing is before they increased it. Its almost double now. They are willing to honor my old price because I have a roof complexity factor of zero. I guess my shed roof decision paid off! (but im still very anxious until its fully installed)

      I should be net producing no matter what. Which is why I'm "ok" with considering resistive heating. But I'd rather save that extra capacity for future EV charging and hot tubs and saunas etc etc.

  7. Paul Wiedefeld | | #14

    This is from a few days ago:

    If you don't want a whole house ducted system, you're using between 1 to 8 outdoor units and many indoor units, all of which will need care and replacement eventually. 1-1 units will modulate better that 1-to-many, but maybe one day the efficiency hit will lessen. It seems like a lot of compromises for a new house that could be designed around a ducted system.

    1. Bernard Lam | | #20

      I read through the whole thing. Very interesting and applicable to me. and oversizing is the obvious first thing to avoid. I'll spend the next few days brain storming how to integrate airhandler or conceal ducted units into my current framing. At least for the bedrooms. You have all convinced me to not put 7k heads in the bedrooms - even my questionable manual J says 1.5-3k for my bedrooms.

  8. Kyle R | | #15

    If you can’t fit ductwork, and your Manual J is correct you might be a good candidate for an air to water heat pump. You can look up SpacePak or Arctic Heat Pumps (there are others) and see if you can find a qualified installer in your area. They have smaller 3k heads and with a buffer tank they are a lot more forgiving regarding cycling. However, they are rare and expensive. Finding a qualified installer is the key, but price might not be much worse than an 8 head air to air quote.

    1. Bernard Lam | | #19

      Lots of products I am not aware of. This might have been worth looking into if I had planned for (yet another) tank in the pantry/laundry/mech room. I started out with an instant HW heater and went to an 80G heat pump, biggest tanked heater in a residential home I've seen. I could barely fit it into the designed space. If I start over, I'd have given the heating/cooling/HW system with 1 outdoor unit a serious look. I don't know if this makes sense for me now....multiple additional tanks, and miles more pex and manifolds to eventually leak. It just look like too big and complicated of a system to integrate to my build now. To be fair, an 8 head minisplit will be lots of refrigerant lines going everywhere too. At least I can keep all of that in the same wall. And if I can figure out a way to combine a few zones with the concealed duct units, that might simplify things.

      The spacepak system might be more applicable to me. Looks much more like a traditional heatpump+airhandler+ducting system, but instead of large ducts (what I'm trying to avoid), its 2" ducts, which should not be a problem to integrate into TJIs and even through steel beams. Does it use water instead of refrigerant? (the red and blue lines between the compressor and the air handler in their diagram.)

      I do see a few reps/dealers for spacepak around me in the Denver area. I might have to call them tomorrow.....

      1. Kyle R | | #21

        SpacePak offers both chilled water and standard refrigerant coils for their high velocity air handlers. There is also Unico and Hi-Velocity. The Hi-Velocity system always intrigued me due to their use of a VFD and integrated zoning system.

        Hi-velocity systems aren’t usually considered the most efficient due to the higher pressure they operate at, but for all of the reasons Akos mentioned in another post they might be a good fit for your house.

        1. Bernard Lam | | #22

          I've read more into all of these different systems. Most of them claim to have installers in my area though when I go to the websites of these installer/dealers, none of them mention these systems. On top of that, the Unico heat pumps sound like they are getting discontinued, on clearance and only 1 year warranty.

          Anyway, a few thoughts about these pressurized systems - The main (maybe only) reason they appeal to me is because its a solution that allows me to have a distributed system without giant ducts. This does solve my needing multiple heads for bedrooms problem. Though using concealed heads + plenum with minisplits still seem like an easier/simpler and maybe cheaper option.

          Another argument is that I need distributed heating to go where my window walls are for comfort reasons. A bit more about these windows. Yes, I do have 1200sqft of glazing, 600sqft of which are on the south side, with a 4' eve overhang. Its a passive solar design that was a product of the limitations to my local energy codes. long story short, they require 50% of my glazing area to face south, but since most of my views are to my E and W (in the mountains with good views), I ended up having to enlarge my S windows. The results are stunning, because giant windows look awesome. But at least some of them I agree are relatively unnecessary. All the S windows. 600sqft of them are floor to ceiling, 4'x8' units. The shading design works too. Lots of solar gain in the winter, yet perfectly shaded in the summer. Other than the W side of course, but thats where the best view is and where my deck is. I accept this doesn't help me at night, where all my windows are losing heat like crazy. I have explored better windows, but my energy modelling shows going triple glazing and +$150k later, it didn't help that much. What I did instead, was to have the entire roof face S, so I get max solar for PV. All 3000sqft of it with no shading. Tesla agreed to install a 25kw system @ $56k after tax credit. This was the old pricing and I consider it a steal, and most certainly compared to triple glazing. So from an energy standpoint I should be net producing, outside of starting a crypto farm (in which case all my heating needs would be met!).

          I have to admit I didn't put that much thought into bringing heat to where the windows are for comfort. I just thought minisplits are the most efficient so I'll use them. Then when I was neck deep in the permitting process they wanted heat sources in every room, so I threw them in the plans. They wanted everything energy star, so I picked ones that are. I didn't read into the issues with multisplits, or how the heat from the heads will be too localized etc etc. Its lack of planning and foresight, and I'm working out those consequences now. Seems to be the same story for every component of this build. Its ok next house I'll plan better :D

          Anyway that's my justification/excuse as to why I'm where I am today. I see that with this high pressure/high velocity system, its all about getting air to mix. I gotta say, whats wrong with a ceiling fan in the great room, running in reverse in the heating season to push warm air down from the ceiling, and promoting air mixing in general? I mean, do I really need heat coming out of the base of all my windows to be comfortable? Where do I draw the line?

          Also, with these window walls, its mostly circulation space. No furniture sit directly up against them. So at least I'm not sitting right in the coldest spot......

          1. Kyle R | | #23


            I would suggest taking a copy of your floor plan and writing the Manual J loads for each room and then upload it. We might have suggestions on how to mix and match some ducted/ductless units. However, you might still want to think about how to address the window walls on a cloudy cold day. Maybe some electric resistance in floor heat or radiant ceiling panels could provide supplemental heat at the window walls to help with comfort.

          2. Expert Member
            Akos | | #25

            High velocity systems do have some benefit but it won't get you duct free. The small ducts can only run for certain length, outside of that you need a supply trunk to feed these small runs. The trunk is smaller than a typical HVAC setup, but it definitely won't fit into a 2x4 wall, typical trunk is 6x6 or 8x8.

            It also adds a fair bit of cost, the equipment is spendy and all the ducting and fittings can really add up. Unless you are looking at retrofit type of situation where you must stay inside walls, it doesn't make much sense.

            You can also use their ducting bits and pieces with a standard air handler. You just need more runs to supply the correct flow.

  9. Robert Opaluch | | #16

    There are a couple other options for small rooms like bedrooms, to reduce the number of heads (besides ducting).

    Window all-in-one heat pumps for a single space. Some fit into double hung or single hung windows, others can be installed on an exterior wall, mounted indoors with two 4" or 6" holes through the wall to the exterior. Some of these units can be plugged into a wall outlet, others require wiring but still pretty simple installation. See:

    Another option is to use RADIENT electric heat units. Radiant cove heaters fit at the top of a wall adjoining the ceiling and direct radiant energy at objects for more comfortably heating the room. There are flat radiant units that you can install on the ceiling (e.g., above a bed or desk) or on a wall. Some claim they are effectively more efficient than resistance heating units, because people feel more comfortable when directly warmed (e.g., from radiant energy from the sun, wood stove or fireplace), or when objects feel warm despite the air being cooler. (The reverse is not comfortable, with colder objects and a hotter air temp, like when a forced air heating system quickly heats a cold room.) Radiant heaters do not provide AC however.

    Resistance electric heaters are a less comfortable choice, but can be very inexpensive.

    Note that if you have a minisplit(s) heating the main areas of the house, with doors open to smaller rooms, much of the heating, AC and dehumidification can be provided by the centrally located minisplit(s), so only spot heating is needed in a bedroom or separate office to provides a heating boost, not 100% of the required heating or AC. Mostly when doors are closed and people sleeping in the room. And people in the room give off some heat as well, which is not trivial in a high performance home. And generally people prefer bedrooms to be a bit cooler for better sleep.

  10. Bernard Lam | | #18

    The Ephoca units are most fascinating! They even have a product that integrates the functions of an HRV. Has anyone here actually used one of these things? How much are they? Can I actually buy them easily?

  11. Robert Opaluch | | #24

    $2,000 is a price I saw, but they have a number of models. I could not get a reply when I tried reaching them last year. Maybe they don't do direct to consumer. Here's contact info I found:
    2000 Auburn Drive, Beachwood, OH. 44112
    216 710-1000
    Please post an article or something if you get anywhere with them or similar products from others, thanks.

    1. Bernard Lam | | #34

      After a lot of emailing and referring, I finally reached their Denver office. Details are still vague but this is what it sounds like:

      They have been in the US for 2 years, units all from italy.

      Distribution network in the US is non existent, and it doesn't sound like they are trying to fix it.

      They are currently supplying a few large multifamily residential projects in Denver.

      I can get a few units for home use, and sounds like anyone can, but every order is a special order, basically you tell them how many units u want, and they will put them on a plane or ship from italy for you. There are no "in stock" units that you can buy. You will pay for the freight however much it costs. For large orders, ocean freight makes sense and the cost is a custom quote by the container load. For a few units, air freight costs about $1500 for first unit, +300 per unit there after.

      The most basic unit each one costs $2200.

      As you can see, shipping direct from italy is what kills the deal. Thats why their only customers are large projects that need 100s at a time. Because then the freight cost is divided to a reasonable amount per unit. Sounds like if people are desperate a "group buy" can be done.

      I plan on going to check out a demo unit, and ask more about warranty and servicing networks etc. Frankly, if theres already established servicing and warranty networks, then not making the simple effort of bringing in a container at a time and sell them online is just bad business development. Any 13 year old can do that on ebay!

      The COP at 17F is pretty low at 1.8 though, I wonder if it even makes sense VS a not so efficient multisplit. I would have really liked the integrated HRV option (which I also want to ask more about), if I hadn't already cut other holes in my envelope for balanced ventilation.

      1. Robert Opaluch | | #35

        Thanks very much for sharing the information. Yeah the shipping cost kills the deal for one test unit, or even a single home. And agree it would make sense for them (or someone) to ship a larger number for sale here with less shipping cost.

  12. Kevin Chan | | #26

    I just finished and moved in my all electric house and let me share my 2 cents. I have a Fujisu medium static ducted unit ARU18RGLX for my second floor, which serving 4 bedrooms, 3 bathrooms, 1 laundry room and 1 master closet. I'm extreme satisfy with this unit, it is very quite, you can't hear anything when it's running except when you get very close to the return grill. Its modulating is so good that the rooms are all equal in temperature. My first floor I have 2 single zone mini splits, 15RLS2YH and 9RLS3YH. These 2 units keep my first floor at 75F with no issue even when the outside temp is 3F. (We have a few cold day this month) My design temp is 8F. The units are very quiets and scale down very good, however, when it is running at a very low speed, the air coming out the unit feels chilly. I think it's because the discharge air is only a few degrees above the surrounding temperature. If you end up going with wall mount heads for you house, you need to consider the mounting location of the heads to make sure it don't blow directly to your beds or couches. Also, each individual head needs it's own drain line for condensations, so plan ahead for that. For hot water, I have the Sanden CO2 with 109 Gallon storage tank and I haven't ran out of hot water yet, and it only draw about 700 watt when it is running. The only issue with it is the tank is very heavy (took 4 guys to bring it down the basement) and the lead time now is very long. (I waited 4 months for it)

  13. Bernard Lam | | #27

    Hi Kyle, I've attached the plans with some notes. Ignore what the architect's placement of the "HVAC wall unit". Boxes in green are where I think I can mount equipment. There is a place to put a ducted unit between the top level bedrooms, and even ducted via the roof trusses to the rest of the top floor, but that means cutting holes for registers into my air sealing drywall ceiling. And the ducts will take the space of roof insulation. But those 2 bedrooms have shared wall which can share a ducted unit. If they make a 7k ducted head that might be a good fit.

    Now that I look at the numbers, the 7k head for the west bedroom doesn't make sense, maybe thats where I should just put a small resistive heater in there just to satisfy code, and expect to never have to turn it on

    The 7k head for the master seem reasonable, and an 18k for the main area of the open plan house would already be undersized, Greatroom/kitchen/dining + entry below and Den above are all connected via stairs opening. 1 head serving all these areas is questionable though, I'd have to somehow promote more air mixing.

    The Den upstairs doesn't need much heating or cooling, so I'm hoping to skip another unit in that common space. The HPWH from the utility room below can be ducted to output cooled air into the Den above. ANd in a similar fasion, maybe an inline fan in the floor to bring air from behind the fridge in the kitchen down to the entry/mudroom.

    In general all the beams are flush beams and run North South, while the TJIs run East West. And I have a lot of steel beams and triple LVL packs. Not much opportunity for ducting. I thought about an airhandler in the utility room ceiling, but the ducts will hit these structural beams to the West and East before reaching the bedrooms above, and going N/S will have to cut through TJI @ 16OC.

    I am not opposed to SOME electric radiant floor heating, since its all tile/wood solid floors. I imagine mostly in bathrooms and maybe selective areas in the dining/kitchen. There should be rugs for the greatroom. The plan is tile for all common areas and bathrooms.

    I assume linesets/drainlines can go in wall/floors, and can go through these beams with smaller holes. Whats the normal size hole to get these lines through?

    The ceiling is flat with vented attic above at the greatroom, vaulted everywhere else. This is slightly different from the plans and therefore the manual J as is.

    The manual J also did not take into account of the wood stove. Honestly I don't know how much I'll use it. It might just be for looks, but if I'm motivated I can use it to heat. I love using the wood stove when I'm on holiday in airbnbs but I have no idea if I'll be using it everyday when i'm at home. Likely only when I have guests. But potentially that stove can heat the whole common area by itself.

    BTW is my cooling requirement a lot? For the upstairs I'm more concerned about air conditioning not getting there. I've also had luck getting upstairs to heat up when its cold out, no matter how old the house, but on hot days, upstairs in old houses are unbearable sometimes. I have a lot of windows but the S ones are very well shaded in the summer.

    I can take some photos if anyone is curious. I've passed framing inspection and currently working on the exterior insulation/siding, with plumbing/HVAC/electrical next. PV/roof after the siding is on.

    1. Kyle R | | #28

      Looking at this quickly on my phone...Can you put a ductless wall mounted unit on the south wall between the two window walls in the great room? This will get better mixing because it will draw the return air from where your heat loss/gain is.

      I would do the same in the master. Put it between the door and the window wall on the south side. You could always go with floor mounts as well if you prefer the look.

      For the upstairs I would go with a ducted unit. The Fujitsu and Carrier slim duct units can be mounted vertically and fit in a small closet. See a picture here:

      Find a place you are ok with adding a small closet to house the air handler. I would suggest the corner between the bathroom and south bedroom. Then run a soffit north along that wall and then turn west and run it along the north wall until you get to the west bedroom. With ducting in that soffit you can hit the bathroom, den, and all of the bedrooms. You will need cooling up here primarily.

      For the condensate lines you will need to run 3/4" pvc either directly outside or to a drain. I would try to route them in a way you can use gravity and don't need a condensate pump. For the refrigerant lines an communication wire you will need about a 4" hole. I would route these through the floor below to where you want the outdoor unit(s).

      I would do 3 1:1 units. Mitsubishi wall mount 6k has the lowest turn down ~1,800 BTU/hr, so that would be best for the Master. But they don't make a slim duct unit that can be mounted vertically. The Fujitsu's turn down to 3,100 BTU/hr. Their ducted units don't come with a base pan heater, but since the ducted unit is for the upstairs, you probably won't need as much heat anyways. Carrier makes ducted units that can be installed vertically and have a base pan heater. You would probably have to mix and match vendors for optimum results, but that's up to you/contractor if its worth it.

      This is the way that I would do it, after my own experience with installing a ductless and ducted unit in my house.

    2. Expert Member
      Akos | | #29

      How much of this is built/permitted? For example can the can you go with lower profile steel beams to give you a path across the house? Floor trusses could also be used in the other direction as they can clear span ~26'. This would avoid any steel plus crane costs to place. Trusses are great for running ducts.

      In general, if you want good cooling performance, the main floor air handler needs a high return near the ceiling of the double height room. This return won't be small, so there is no way to burry it in a wall but could be run on the inside of the rooms in a corner.

      For the big windows, you want a register in the floor or in the ceiling above. If getting ducting there is not possible, you can go with a strip of resistance floor heat. The HVAC would still supply bulk of the heat, but the bit of floor heat will help take the edge off of the cold air downdraft from the windows.

      For a clean install, a liner diffuser is the best but does take up space:

      1. Bernard Lam | | #30

        Its all there :-)

        Every inch is engineered and permitted. My engineer signed it off recently. 2 stories with daylight basement and very open plan makes a tall hollow box in an area with high snow loads and 165mph design wind speed means LOTS of steel. Luckily I like the look of exposed steel. Frankly, we should have engineered that tall west wall to be framed with steel too, instead of a whole wall of 10" LVLs balloon framed. But material prices fluctuated so much in the last 2 years we thought it would have been cheaper doing it in wood as much as possible. Not true by the time I ordered the wood. At minimum that 16' header should have been steel. Right now its a 3 pack 12" LVL box header.

        I think electric floor heating in front of the windows might be my best option.

        Kyle I'll go on site and take a good look at your suggestions and see if I can route the lines to those locations and ponder what it looks like with the units in those locations. 3 compressors outside is a bit hard to swallow, maybe stack one on top of another or something. I dont have unlimited space back there. Also, directly above is a deck and hot tub hang out area, so I don't want the noise to be TOO loud. I wonder how 2 or 3 single units compare to 1 multisplit in terms of noise. Anyway thanks a bunch!

        1. Kyle R | | #31

          No problem. Awesome house BTW. A multisplit can work, it’s just not as foolproof as 1:1s.

        2. Expert Member
          Akos | | #32

          Steel in exterior is hard to deal with. A bit of exposed steel can make for a pretty big thermal bridge and sometimes even condensation risk. LVLs, even if more were the right choice.

          For reference north means up.

          Since its built, you best bet is to work within it. I'm assuming the crawlsapce is conditioned. If it is not, it really should be, without that, the floors above it will never be warm enough without floor heat.

          I would put a multi position air handler in the crawlspace and run a supply trunk just under the floors on the north wall all way across the house. This does mean some extra insulation and air sealing of the section in the garage. Since the garage is already insulated, it should be a big additional loss. From this trunk you can now run takeoffs along the floor joists and reach everywhere on the main floor without the steel getting in the way. This would put the register right under the windows in the living space.

          For the 2nd floor, I would put a slim air handler above the top of the stairs. A bit of height lost there will never be noticed. From there, it is a simple shot to the rest of the rooms through the hallway. The important part is the return for this unit should be near the ceiling to get good cooling for the 2nd floor.

          I would definitely not put a wall mount in a bedroom. Since you have a lot of solar gain, a zone for the master does make sense, I would go for a slim ducted unit in the crawlspace or in the ceiling of the utility room.

          The main floor plus master could be on a multi split. The 2nd floor should get its own outdoor unit.

          EDIT: Got your floor joist orientation wrong. You would have to run a trunk along the wall than under each steel beam. From there up into the floor joist area.

  14. Bernard Lam | | #33

    Thankfully I don't have any exposed steel to the outside. Its at minimum wrapped by R20 worth of XPS. All the exposed steel is in the interior.

    I have a few basic questions:

    1. How large would these air ducts be in diameter? what about in rectangular form?
    2. What's the rule of thumb size of hole you can cut into the web of a TJI before needed extra reinforcement?
    3. For the line sets, Kyle mentioned 4" hole, does that mean line sets cannot be routed through (inside) a 2x4 walls?
    4. Are there any in floor, between floor joist, or in wall, between wall studs electric heaters that people recommend? I'm wondering if a few resistive heaters in the bedrooms makes more sense than HP heads, It'll certainly be cheaper. Maybe just for the West bedroom that is hard to route ducts to.
    5. Or an installed equivalent of an electric oil radiator for more slow radiating heat? (This is common in Europe)
    6. Are there effective ways to air seal a supply register to an air tight ceiling if I decide to duct through the roof trusses? Would this be recommended?

    I don't know about cost, but something like this might be the best I can do for in front of the window walls, like a heat wire in a ditra equivalent, under tile. Or maybe I can apply this to the bedrooms that won't get a HP head too.

    1. Expert Member
      Akos | | #37

      1) Main trunk needs to be sized for the airflow through it. Typical house you are looking at a 16x8 trunk. I'm in the land of hard pipe HVAC installs, so a main trunk is always rectengular duct.

      2) Check the install manual for your I-joist. You can cut a surprisingly large hole through most as long as you are not near a load bearing point. I would try to minimize running ducts across I-joists, try to come up with a layout that makes most of the runs along them.

      3) Min hole size for most heat pumps is around 3". You can use smaller if the drain is seperate, which it should be for a new install, maybe as small a 2" can work but more makes pulling the line easier. You want the drain line to run to existing plumbing inside the house. Take care with long interior lineset runs as there is a fair bit of thermal expansion when running, you need to allow for this otherwise they will "tick" which is very annoying (and hard to fix after the fact).

      4) You can go resistance heat but you won't get cooling. Looking at your layout, if the 2nd floor unit is in the ceiling on the south side of the house, you can run a supply line along the inside of the closet and above the door to the bathroom.

      5) There is nothing special about any type of resistance heat, they all work about the same. IR radiant heaters do work better when you want to provide local heat in a an unheated space, but that is about it. You can use any type of resistance heat you want here, base board, cove heater, heated ceiling tile or floor heat. All would work just as well.

      6) Running ducts through a roof is a very bad idea. The better option is to install an air barrier under your trusses (ie taped OSB is perfect for this) run ducts underneath than install a drywall ceiling bellow the ducts.

      For floor heat, I like the Schluter parts but any quality resistance mat will work. Make sure to run the temperature sensor in a small PEX pipe (5/16" or 3/8" pex is great for this). This way if the sensor ever fails, you can replace it without pulling up the floor.

      1. Bernard Lam | | #38

        re point 6, running ducting through roof - if thats a bad idea, would running ducting through an insulated soffit be just as bad? Its essentially a roof. directly under the south wall (windows) is 4' of cantilever, i.e. not living space. Its a soffit that wraps a W18 steel beam that runs the entire length (E/W) of that cantilever, with the 3 W18 beams (N/S) attached to it. You can see it in the section views in the plan.

        Of course, I may not have enough clearance to put a 6x18 trunk with sufficient insulation under the 3 N/S W18 beams anyway, which makes this conversation moot. I'll have to go double check the difference. I do know that I had that soffit framed lower than the plans show, but how much insulation do i need to wrap these trunks with?

        I dont know why the previous post was deleted, I thought his experience was very applicable to mine. And it was a great photo showing his double height space. Just missing a wrap around deck!

        1. Expert Member
          Akos | | #40

          You never want ducting to poke through an air barrier. So depending on where the air barrier is in your soffits, running ducts there might be ok.

          Sometimes including a bit of sprayfoam in overhangs is worth it as it simplifies air sealing. Ideally you want simliar R value around the duct as your floor overhang R value, basically all your insulation between the duct and outdoors. Because of diminishing returns, even going as low as R20 is fine, the coule extra hundered BTU lost here is nothing compared to your glazing losses.

          P.S. Triple pane is usually only worth it to increase comfort, there is almost never ROI for installing it. I don't know exactly what you are using for windows, but triple pane should only be about %15 more for a fixed window. I've gotten quotes for tilt and turns where the extra cost was so low that it was a no brainer.

          1. Bernard Lam | | #41

            I noticed in Beopt they have some pricing data, and in it also shows about a 15% increase in triple glazing. I was shocked. But I think its because theres a much bigger cost difference between different lines of windows, and most of the more cost effective model lines simply does not offer triple glaze as an option.

            I have andersen 100 windows, 40+ of them, and only 4 or so are casements (egress) all others are fixed. For better air sealing, and less maintenance. Most would consider the 100 series a contractor grade window and puzzled at why I use it for a custom home. But its fits a lot of my requirements. I wanted a low maintainance material frame - i.e. no wood, no aluminum/vinyl clad wood. I am sick of re staining/painting wooden window frames that gets destroyed in CO sun+snow. (same deal with decks). Obviously aluminum frames are not insulated enough, even for thermally broken ones. That leaves fiberglass or vinyl. Vinyl is not allowed in my area, I think because of fire concerns, they melt too soon. So its fiberglass or, fibrex, the composite that andersen 100 uses. Frankly, I really like the window. They don't look or feel cheap, and operates as nicely as their more expensive A series etc. Very high performance to price ratio. Anyway, I don't think they offer a triple glaze option in the 100 series, and more importantly, I would not have been able to install them with man power on pumpjacks. My windows are big enough that it'd be too heavy in a triple glaze version, and require a crane, but theres no crane access because of the steep site. Anyway, when I explored the option of triple glaze, I had to go with a much higher cost series/brand, and have units that are too heavy to install. Installation usually cost as much as the windows, and in my case, with all the site difficulties, double the cost of the windows. Add all that complications together, my triple glaze option was at least a 300% increase in cost.

            I was very impressed with the alpen "suspended film" technology though, the R value of a triple pane, but the weight of a double, and cost very competitive.

            I'll look into my clearances at that soffit tomorrow. I did originally plan for the floor sheathing as the air envelope for simplicity, in which case, again, I'd be punching through that. It breaks my heart to go resistive (I call it toaster) heating but in floor heating mats might just be easiest and makes the most sense. If just supplemental. I was going to do that for the bathrooms anyway.

          2. Expert Member
            Akos | | #42

            High altitude is a whole different game. Your choices are definitely a lot more limited.

            For heavy windows, one option is to go flangeless and install them from the inside. The only that needs a couple of burly Czechs.

  15. Deleted | | #36


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