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Community and Q&A

Do I really want a ducted mini (vs ductless)

maine_tyler | Posted in General Questions on

Should I believe in ducted splits?
Quite a few respectable voices on this site advocate for ducted heat pumps over ductless. When I tell local installers I would like to consider a ducted mini split system, they tell me that there is NO ADVANTAGE to a ducted systems (or that they simply don’t mess with them) and further that they are actually disadvantageous due to being more expensive and less efficient. Why mess with them!? I don’t push back a lot because I don’t have the depth and breadth of knowledge (or desire) to convince contractors that they want to install or retrofit ducts if that’s not what they want (or know how) to do. To be frank, the arguments made here in favor of ducted systems I perhaps only *sort of* get (namely better distribution and better filtration). There are positives to ductless we need to weigh the positives of ducted against.

I found this interesting article by Allison Bailes from 2011 where he said the following:
when I get a chance to build a house for myself again, I’d like to eliminate the ducts by using ductless mini-split heat pumps, and Mitsubishi is one of the top brands.


Here’s why I want to go ductless:

  • Duct systems can be done right but almost never are, thus robbing the heating and cooling system of its effectiveness and efficiency.
  • Duct systems take up a lot of space in attics, basements, and other parts of the house.
  • HVAC technicians don’t understand – and often don’t care about – ducts.
  • Mini-splits are some of the most efficient systems (up to 26 SEER).
  • Mini-splits come in smaller sizes and can better match the heating and cooling loads in the house.”


I don’t know if he’s changed his tune, but his point that ducted systems are difficult to do well could be a deal breaker. If none of the local contractors want/know how to do this, it seems destined for failure. If they want to sling ductless, maybe I should let them because it’s what they know how to do and won’t (completely) mess up.

Better modulation and humidity control with ductless?
Allison’s point that ductless units allow a lower turn down (not just per a unit but system wide output) also has me wondering: wouldn’t this translate into better humidity control on mild summer days? A ducted system seems to essentially be more like a multi-head system in that there is one outdoor compressor controlling (and modulating) for the entire house load. 1:1 ductless  seem to have the most flexibility, efficiency, and modulation. It’s just the bedroom thing…

But there are still bedrooms to condition
Somehow I do need to solve the issue of distribution into bedrooms/bathroom/small spaces that admittedly ductless seem hard pressed to do. 

Despite having an existing furnace with ductwork running every which way, I have considered doing a couple 1:1 ductless units with one low static horizontal ducted unit (new ducts) to serve a couple small spaces. I also run a woodstove, so being able to zone out that room (using a ductless head) would be better than having one zone for the entire house as with a multi position air handler. But the solution of running one slim ducted unit in addition to ductless I imagine is both expensive, and it doesn’t solve the issue of having to find people that are able, willing, and excited to install quality ductwork. I am also not sure if the floorplan is entirely conducive to running a slim duct unit to the small rooms where I don’t want a head.

What’s a person to do?
In case anyone is interested in getting into the weeds rather than generalities, I’ve attached a floor plan. Existing furnace is oil (massively oversized short cycling beast), water heater is electric resistance. Woodstove is in living room. Full basement, full attic over living room, partial triangle attics with dormer for the 1.5 story main part, and cathedral in sunroom. Insulation and air sealing is average, but with plans to improve low fruit like basement rims, attic triangles, etc.

Finding a contractor
A local question: Does anyone in Maine know of reputable HVAC designer/installers that actually do ducted mini split systems and believe in them? I have only found a few heat pump companies that said they could do ducted, maybe, but it’s not their forte and they really tried to talk me out of it.

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  1. Expert Member


    I almost always stay out of heat pump discussions because the are a lot of posters who know much much more than I do about them, so take this as something by an interested but poorly educated observer.

    Where I am many houses have a primary central heat source - usually a wood-stove - and supplemental electric resistance to boost remote rooms. Recently more people have been replacing or twinning the central heat source with one or two ductless mini splits. That's where I think they shine. You get the great majority of your heat from a very efficient and simple setup, and use the supplemental heat source as a fine tuner. The question I guess is: Is having to use some less efficient electric resistance worth it to be able to forgo the complexity of ducting, and the ability to zone remote rooms? For me it would be.

    1. maine_tyler | | #7

      I appreciate hearing your perspective on this Malcolm.
      That's actually quite interesting and seems reasonable. I admit I have a hard time swallowing resistance heat for anything other than very minimal AUX backup/coldest day sort of thing. Partly because the efficiency is just so low, and electricity prices here in Maine/NE are quite high.

      But if the amount of total energy coming from the resistance is low enough, I suppose it might not make the overall system terribly inefficient and is certainly dead simple to install.

      1. Expert Member
        MALCOLM TAYLOR | | #11


        The equation here is skewed by our temperate climate and low electricity prices. Our all electric house, heated sometimes by the wood-stove and often just by electric resistance, averages jut $7 a day. I'm not sure there are many useful lessons for you in New England.

  2. paul_wiedefeld | | #2

    Great question! I have many thoughts here:
    1. For context, most Americans already have ductwork. It’s the most common distribution method by far. It’s imperfect in many situations, but people aren’t lining up to replace it so “pretty good” describes it well. That’s to say it works for most everyone and contractors know it well. Probably less so in Maine.
    2. Backup heat is easily incorporated in ducted systems, either furnace or resistance. This is great - you can size perfectly for cooling and let something else cover the low % of heating that’s beyond the capacity. You can also maximize your electric panel - a furnace that runs for 10 hours a year can prevent a costly upgrade. This is also great for when the power goes out - you’ll need a generator still, but a much smaller one.
    3. Dehumidification is stronger - usually the high SEER ratings some ductless units have come at the expense of moisture removal (creating warmer coils = less dehumidification = greater efficiency). Other auxiliary dehumidification options aren’t great - either loud, inefficient, inexpensive and portable or expensive and ducted, so you get a huge benefit here.

    See this amazingly efficient Mitsubishi ductless with near zero dehumidification ability. Great for some climates, but moldy in mine.

    4. The choice is rarely ducted vs multiple 1:1 ductless - it’s usually vs. multi-splits. Multi-splits, to date, are poor products. They are not efficient and their turndown is terrible vs. ducted. You’ll have a small room (or three) that either go unconditioned or get a unit way oversized. At the same time, the outdoor units have worse turndown and come in lumpy sizes - you might have to exceed your indoor load by a lot to fit the number of heads you’re trying to connect. This is especially bad on the smaller end of heat losses - the <30kbtu loads with 4-5 rooms you could put a head are a huge hole in the multi-split offerings. This is all inefficient and uncomfortable. If the argument was 1:1 ductless vs ducted, I can see some points for ductless. It wouldn’t be cheap for the larger installs though.
    5. Ductless heads are louder than ducted systems. They’re quiet, but less so than ducted. There are beeps, fan speed and vane changes.
    6. Ductless systems will not be maintained like ducted. It’s extremely easy to replace a high quality ducted filter - it takes maybe 30 seconds a month. Ductless filters are nearly nonexistent and deeper cleans are difficult.
    7. Aesthetics: totally a personal preference. I don’t mind my ductless unit’s appearance but it is there. It might bother others more.
    8. Cost effectiveness: a ducted system is cheap: the ductless unit for only 1 room was 2/3rds the price of the cost of the ducted system for the rest of my home - same manufacturer, same installer. A lot of that process is redundant. However, I had existing ductwork. Ductwork has a lifespan beyond a heat pump, so replacements are less expensive. For ductless, you’re starting from scratch minus the easy stuff.
    9. There’s a weird product placement issue I frequently see: a high end multi-split will be offered alongside a crappy ducted unit. In that case, the multi-split technology is of course better, but it’s unrelated to the ductless attribute. The fair comparison is ducted vs ductless with the same qualities, but contractors don’t always do this and I have no explanation why.
    10. I wonder if expanding your search to all ducted units might give better results. The guys that do almost exclusively ductless are probably not the ones you want installing ducts. But the Trane/Carrier/etc ducted units installers might have the skills you need. These aren’t “minisplits” but that doesn’t matter, they’re highly efficient and high quality options. The one knock I can think of is cold climate offerings, I’m not up to date with that. That’d be solved with a hybrid system anyway.

    1. maine_tyler | | #8

      Those are some great thoughts Paul.

      In terms of the cheapness and ease in which ducted systems can be installed, worked on, and maintained, some of that could very well down to regional differences (can you remind me where you're at?) That said, even Allison who is in an entirely different region made the point that it is seldom done well. My understanding is that to get a really efficient and well performing ducted heat pump system, you really need well designed/installed ducts.

      One contractor who was talking me away from ducted said that 98% of the time to do a ducted retrofit they would just tear out and replace the old ductwork. I think he was talking out his behind a bit with the 98%, and it sounded a bit like a liability thing because they didn't want to 'own' the problems with the old system. Granted he said all this before even looking at what I had for ductwork (which tells you something about his mindset-- he was measuring a wall for a ductless unit--without me indicating that's what I wanted-- before I could get him into the basement to look at the ductwork).


      When it comes to comparing systems, I think we are looking at at least 3 elements:

      PERFORMANCE-- how well it accomplishes the goal of conditioning the space, including humidity removal, delivered comfort, noise, filtration, reliability, user interface, extreme temperature performance, etc.

      COST-- Upfront and long term, so this includes efficiency. It also must consider other system costs that may be displaced or added in one case or another. I.e. if one system can dehumidify and the other one can't, the cost of a standalone dehumidifier should be considered for the latter.

      AVAILABILITY-- product availability as well as installer/designer, and maintenance support. Also the availability of confidence that the system will be installed correctly so that the performance metric is not compromised.

      I can get on board with the notion that the PERFORMANCE of a well designed and installed ducted system does better on many or most performance metrics than ductless. I am a bit less convinced of cost, especially if we want to have that availability of confidence that it will get done right. It is that last metric--availability-- where I think the ducted route may take a nose dive. Particularly the availability of confidence that the product will be installed to perform at optimum. The installation is so involved (manual J, S, T, D!) that the availability of all that knowledge and skill is in short supply! I don't mean to say it isn't a worthy pursuit, and perhaps in some regions it really is not all that difficult! I may still try, but I am not sure.

      As far as multiple 1:1 vs multi-split ductless, the comparison I am most interested in is the multiple 1:1 route. I am not sure what you mean by "the choice is rarely ducted vs multiple 1:1 ductless" unless you just mean installers don't often default to multiple 1:1 units.

      1. Expert Member
        DCcontrarian | | #9

        I find that HVAC guys like to badmouth other members of their profession more than any other trade.

      2. paul_wiedefeld | | #14

        My perspective is more aligned with my first point - ductwork is mainstream, ductless is not. I find it unlikely that the millions of ACs and heat pumps are all attached to disastrous ductwork. I think you’ve talked to ductless specialists thus far, which makes sense in Maine. I’m in Maryland, so the AC in HVAC is a must. That means ductwork effectively. I think the decision for most Americans involves no manual Js, Ss, Ts or Ds - they’ll attempt to reuse the ductwork that their existing AC + furnace was using and that’s usually the end of the story. That really eliminates much of the skill involved frankly. The northeast is a bit of an outlier here, take a look at the EIA’s energy consumption surveys sometime, ducts are king and heat pumps are widespread. The hot water and steam with no AC of the NE is the tiny minority of US households.

        “I am not sure what you mean by "the choice is rarely ducted vs multiple 1:1 ductless" unless you just mean installers don't often default to multiple 1:1 units.”

        You understood correctly - multi-splits seem like the recommendation over many 1:1 units. I understand why, that’s a lot of outdoor units hanging on a house.

        1. maine_tyler | | #26

          My sense is that while domestic warm weather ducted heat pumps have been common for a while, cold weather pumps are relatively new and when they hit the market they were heavily pushed as ductless. In other words, I really don't think this is a super isolated issue to a small New England segment, but basically any cold climate scenario. There's lots of posts on GBA of people facing this challenge that bears this out (anecdotally). E.g. installer wants to install 7 heads. Maybe they're all in the northeast, not sure.

          My understanding is that ductless cold climate pumps are also more common in other parts of the world vs ducted, so there may be a manufacturer bias. I could be way off here; that is just my sense.

          The point being that lots of people looking at cold climate heat pumps are facing this issue and the prevalence of ductwork in U.S. homes, generally speaking, doesn't really make this a simple matter for many.

          Have you seen Jon Harrods piece on planning for a furnace to ducted heat pump retrofit? He implies that a mindless box swap (which sems to be what you suggest should be the norm- i.e. nonload calcs, no duct testing, etc.) is a recipe for poor performance given the different requirements of cc heat pumps.

          1. paul_wiedefeld | | #30

            I haven’t read the pieces, but it’s so cheap to include a low end furnace, resistance strips, or keep the existing furnace, I think this problem (needing more airflow then the ducts can provide given a lower air temp) is solved. Will the ductwork be perfect? Unlikely! But it’ll perform just as it did before. There’s not a true difference between cold climate and warm climate installations besides familiarity, an undersized duct or undersized heat pump has the same fix across climates.

    2. maine_tyler | | #10

      RE humidity.

      I am interested in this bit of performance comparison. I found this GBA thread where it was implied that the high SHR numbers in the Mitsu specs may not resemble operating reality.

      I would be interested to delve into this topic a bit more though. For example, the idea that the SHR is poor because the coil temp is so warm... doesn't that imply that CFM would have to be very high to deliver the needed cooling (for a given cooling load) compared to a cooler coil? If so, does this imply that a ducted unit with better SHR will move less air than a ductless unit for a given cooling load? I was in front of an FS-09 in cooling mode recently and it didn't seem to be delivering that much air, so it's a bit hard to believe the blower on a ducted unit would deliver less...

      Perhaps another question is: for humidity control, does the SHR of a unit matter more, or does have a low turn down and right sizing matter more. I suppose I was thinking the 1:1 ductless unit have the edge on the latter front, but I had not considered the specifics of the equipment operation.

      1. Expert Member
        DCcontrarian | | #12

        SHR is kind of a derivative measure. Unless the indoor dew point is already below the coil temperature, the lower the coil temperature the more humidity will be removed and the lower the the SHR. For heat pumps the COP is always dependent on the delta between hot side and cold side, so the lower the coil temperature the lower the COP. So manufacturers will try to boost the COP by raising the coil temperature.

        What controls the coil temperature? There are two factors that can be controlled, the compressor speed, which controls how much refrigerant flows into the coil, and the blower speed which controls how much air passes it. The higher the ratio of compressor speed to blower speed the colder the coil, and vice versa. The refrigerant flow determines the total amount of cooling provided, which presumably is matched to the load, so it's really the airflow that can be adjusted (within limits, the airflow also has to support the load and the coil can't be allowed to freeze). So at any cooling load, the higher the airflow the higher the coil temperature, the higher the SHR and the less dehumidification provided; the lower the airflow the lower the coil temperature, the lower the SHR and the more dehumidification.

        Chiltrix has an interesting feature they call "Psychrologix." You provide setpoints for both temperature and humidity. The controller adjusts the coil temperature to maximize COP while meeting both setpoints.
        (see )

        1. maine_tyler | | #15

          "So at any cooling load, the higher the airflow the higher the coil temperature, the higher the SHR and the less dehumidification provided"

          This makes sense and is the logic I was heading towards. What is confusing then is why a small ductless unit would have so much higher airflow than a ducted unit. It just doesn't seem like that much airflow in front of the ductless units in cooling mode. Though I also haven't experienced the airflow of a ducted unit so maybe it really is less.

          1. Expert Member
            DCcontrarian | | #17

            I pulled together some real(ish)* numbers. Let's say your house is at 75F, 50% RH. It's summer and the cooling load is 3,000 BTU/hr, the compressor is supplying refrigerant to provide that level of cooling.

            Scenario 1: The blower is providing the rule-of-thumb 400 CFM per ton, or 100 CFM for the quarter ton. The exiting air is at 52F, 100% RH. The latent cooling is 547 Btu/hr, the SHR is 84%.

            Scenario 2: You go for maximum dehumidification, you reduce the airflow to drop the coil temperature to 33F. With the same 3000 BTU/hr of cooling the air flow is 42 CFM. The latent cooling is 1,092 BTU/hr, the SHR is 64%.

            Scenario 3: You speed the fan up to eliminate any latent cooling. Coil temperature is 56F. Exiting air is 98% RH. Fan speed is 146 CFM, SHR is 100%.

            *( Here's where the numbers come from: I made up a spreadsheet to calculate latent and sensible loads for various combinations of temperature change and air flow. You can see it at:
            Coil temperature is assumed to be leaving air temperature)

  3. AndrewJohn | | #3

    I'm in a similar boat but in Denver. ~1400 sq feet between the first floor and basement. Pretty standard 1920s bungalow layout. Living room, kitchen, den, bedroom. It's been a nightmare trying to get an appropriately spec'd system. Did an energy audit, some of the thermal pictures are hilarious.

    They did do a blower door test so I attempted a manual J on cool calc. I'll probably run a second just to validate when I'm ready to pull the trigger. Tried to be as accurate as possible with windows sizes, equipment and all that. Whole house is about ~25k heating after we blow 19 inches of cellulose back into the attic.

    This is a fair amount of word vomit but here is how I worked through things and it may be helpful. You have to compromise and\or be extremely assertive with the installer if you aren't going to do yourself.

    The quotes I've gotten from some of these people are hilarious. None have been willing to discuss a ducted or partially ducted system.

    The first one - Mitsubishi diamond dealer - was for a 48k multi split. $22k for 4 zones $29k for 7 zones. (off to a really good start). Egregiously oversized and would have been a waste of money.

    The second one - for the basement alone they wanted to put a 15k head in. Then upstairs they wanted to put 2 or 3 9-12k ceiling cassettes upstairs. So again we're talking like 36-48k BTU's. I mentioned to this bozo that I did a manual J calc and that the basement should be just a 9k and he said "nah, I do this all the time you'll want 15 down here just to be safe". As soon as he realized I was doing our electrical reno myself he didn't have a lot of interest in the job and I never got a quote. Kept mentioning rebates and stuff. This is one of those things where I don't know if the rebates are a blessing or a curse.

    Both recommend putting cassettes right over where the oven (with no exhaust) lives now which does not seem like a good idea.

    I have a third feller coming in tomorrow and we'll see what he says and then I'm just going to get a quote on the following since ducting is impractical - all hyper heat models (if the price isn't reasonable I'll just get my EPA cert and do it myself):

    FH06 in the bedroom pointed towards the door. FH09 to hit most of the common area upstairs and an FH09 for the basement. These all be 1:1. Not keen on a mini split farm outside but it's the best solution I think. It is maybe slightly undersized but based on the submittals - there seems to be enough overhead to compensate for the "rated" BTU's.

    The bedroom load is allegedly 36ooBTU with the north facing not insulated walls and big windows. The 6k unit should modulate enough to be relatively efficient even if we wrap the house and replace the windows. Any other product would be massive overkill and it being 1-1 it can be turned off when not needed. 2 6k ducted units in a conditioned attic is probably more ideal for our layout but no one makes a 6k ducted unit (though I think Fujitsu makes a 7) but either way that isn't practical from a cost or time and effort perspective and the Fujitsu wall units don't (on paper anyway) modulate as far down as the Mitsubishi.

    How do I know this should work reasonably well? I can cool my first floor reasonably well with a 12,000BTU Midea U-shaped air conditioner with one ceiling fan pushing air into the kitchen and a little (loud) vornado blowing cool air down the hallway to the bedroom. The bedroom does get warmer since the airflow there isn't great but it's a solid starting place for a proof of concept. +15k of heating should be no issue in the main living space even in zone 5 and the two units being able to modulate down to ~3400 BTU combined should keep those things running at a happy clip.

    Anyway, the bedroom unit may cycle a bit because its a bedroom and were compromising. Yes I could do ducted but the loads between kind of adjacent rooms is over double so I'd have to play games with duct size and go down that rabbit hole, plus there's a few walls and a closet that need to be traversed and I'd have to drop a ceiling so its a huge PITA and major construction project.

    Based on what I've read here and the internet at large, for a reno there isn't a perfect solution. I want to get rid of my central system to reclaim 150 sq feet of floor space and I'm sick of banging my head on ductwork. With the size of our house, usable square footage has more value then reusing the existing central system and the slim ducts require a fair amount of space themselves which I'm not willing to accommodate in the basement.

    So based on our goals with the house and what were willing to tolerate temp difference with organic air movement through open spaces and doors - it should still be more comfortable than our current heating solution and lack of central cooling with the benefit of being more efficient while making an unusable room usable now and onestep closer to removing the gas appliances in the house.

    I think you have to get a little creative and really think about what rooms need to be directly conditioned and what rooms you can get away with them eventually cooling off or heating up.

    If your building envelope is pretty solid, or like my case where you just don't have a lot of square footage, fewer heads pushing more air with open doors is probably more comfortable/tolerable then you would think.

    1. cs55 | | #6

      basically my experience.

      1500 sqft in oklahoma, so its decently warm and somewhat humid here. one bedroom has a 1 ton minisplit, and a bedroom on the complete opposite side of the house has a 1.5 ton unit.

      if its 105f outside and the minisplits are set to 70, the warmest room in the house will be 72. however, where this falls short is when people are going in and out of the house. temperatures can quickly raise and take awhile to recover in the kitchen/living room(one open area) since there is no air handler/vent in those rooms.

      last winter when it was down to about 3-5f, it did get a little cold. but the minisplits are only rated down to -5f. my attic insulation is really bad and the 20 year old aluminum single hung windows that would literally have ice on the interior side have been replaced with tilt and turn windows. so hopefully next winter will be a little more comfortable once the insulation is fixed this fall.

      1. AndrewJohn | | #16

        That's the experience we're going for.

        1. cs55 | | #19

          its been around 100 with a heat index of 110 the past couple of days. so humid.

          the living room has about 30 feet of exterior west facing wall, with a glass sliding door, and 2 ~36x84 windows that have no overhang or an awning.. is decently warm by the windows. hopefully this weekend the new windows will be installed.

          but you can see how much the temperature will peak at 6 pm when the sun starts to hit that side.

  4. 1910duplex | | #4

    I did ducted minisplits for the upstairs (about 600 sq ft) of my not-at-all-tight 110 year old duplex. Fujitsu. The ducts and handler are in the attic. I had already insulated at the ceiling of the attic a few years earlier b/c it is a walk up attic, so it was impractical to air seal at the floor with that giant staircase.

    My installer did not do a perfect job of the ductwork -- it failed a duct blaster test, and there is a little spot of moisture stain in the plaster of one of the ducts in the master bedroom -- but the system is still not using a lot of electricity and is effective. They came back and allegedly improved things, but we haven't had another duct blaster test.

    Last June 15th to July 15th, where we started running it daily probably the last three weeks of that period, it used 658 KWH

    July 16th-Aug. 12th, 590 KW (ran every day until Aug. 6)...

    post duct tightening, we started running it July 3rd in the evening when we got home from a trip. It does struggle to get down to the set point when you come home to a 93 degree house! Used 17 kw that day, 34 kw the next day as it was still trying to catch up and doing lots of laundry, and then 19-23 kw to keep up with 24 hour periods where the average temp is 79 or 80 (about 90 as high, about 72 as a low)

    our base use for small dehumidifier in basement and fridge with no one here at all is 7kw daily

    Before installing this, we had a window unit in our kid's room and one in the former sleeping porch off the upstairs home office, and suffered with no A/C in our room and the rest of the house... comparison for that half June/half July was 513 kw, and about the same for July/August bill. And those window units only ran 12 hours a day.

    We set the hallway thermostat at 80 degrees (where the return is), and the bedrooms range from 72 at the low point overnight to 77 in the peak afternoon (except the home office, which is south facing, which runs close to 79 during the day)

    We scraped the paint off the edges of our transom windows so the conditioned air returns to the hallway when the doors are closed.

    We got a system that could take over as heat when we're ready to get off natural gas boiler/radiators, but haven't really tried it for that because we have no minisplit arrangement on the first floor.

    But the first floor even with no a/c is much more comfortable much of the day with the lower humidity the system upstairs maintains.

    The downside -- it was expensive. About $15k. (not counting the cost to do flash and batt in the attic ) But there would have been no way to serve the bathroom, the sleeping porch/tiny third bedroom with individual minisplits, and an individual minisplit in the moderate size bedrooms was way too big for the cooling loads and was even too big for the heating loads.

    I'm hoping when we decide to go minisplit for heat (I'm nervous, b/c of our lack of insulation in the walls) that there will be a way that makes sense to use a wall mounted unit or two downstairs, but I think it would have to be the ones designed to sit in the same place as radiators because of our layout -- the three rooms downstairs, the walls that face the length of those three rooms have large windows taking up all the high wall space.

  5. nynick | | #5

    This industry is a nightmare. You don't know who to rely on for design, install or system selection. The GC's don't care enough to educate themselves and the homeowners are ignorant on the specs (like me!). GBA is great for advice, but it really shouldn't be this hard to find qualified, dependable and accurate installers in the field.

  6. Expert Member
    Akos | | #13

    Short answer is yes. There are very few cases where a wall mount is the right answer.

    The efficiency difference between a wall mount and a ducted unit comes down to blower power, it takes more power to move air through ducts. You can always reduce this difference with good duct design though.

    For anything new built, I would not bother with wall mounts. Retrofit is harder but even there, I would try for a ducted unit unit at least for the smaller rooms.

    Many moons ago I made the mistake to install an oversized multi split with a bunch of wall mounts, if the unit ever fails, it will be replaced by a ducted unit.

    1. maine_tyler | | #25

      Your voice is one that came to mind with this question. Would you care to summarize what benefits you see with the ducted option?

      As a follow up, do you think someone like me should be concerned with the lack of local know-how to implement proper duct redesign in an existing building with an old oversized furnace with leaky rectangular trunk and round branch ducting in the basement?

      If ductless I would avoid multi split in favor of 1:1.

      1. Expert Member
        Akos | | #28

        I've done a retrofit of a hydro air coil into an older furnace a while back.

        This is similar to a heat pump retrofit, if you want good efficiency you need to keep the water temps low so you need more flow per BTU delivered.

        Since the original furnace was oversized, like almost all out there, the existing ducting was mostly not an issue. Did have to replace a very restrictive fitting in the return air fitting but that was mostly because it was wrong to leave it.

        Even though the new coil was much lower BTU and the delivered air was colder, the place was much more comfortable as runtimes were much longer.

        There are definitely a lot of bad ducting out there. Lot of times fixing it won't make financial sense but it doesn't mean you can't swap in a heat pump and in most cases it will work better. Checking the exiting ducting is relatively straight forward, a home owner can do it with a $75 pressure gauge.

        As for ductless installs, the main issue is the smallest head is too big by at least a factor of 2. I think the Mitsubishi SM series has some 4000BTU in-wall units that could be made to work but even there the smallest outdoor unit does almost 4 tons of heat.

        The minimum airflow on even the smallest indoor wall mount unit is also too high which creates issues with placement and comfort.

        When you are looking at these 1000BTU to 3000BTU heat loss numbers, the simplest is a duct to supply it. The register can now be placed where it works best. You can also now use this ducting to supply fresh air to the room which can't be done with a wallmount.

        Also having dedicated equipment for each room creates too many issues with noise and maintenance down the road.

  7. drewintoledo | | #18

    I installed both ducted and ductless

  8. entropic | | #20

    Thanks for this discussion.

    I’ve asked this question elsewhere but haven’t got an answer yet. I’m sure someone on this thread might know. Why is it that only ductless units have the -13/-15 F ratings? I think the coldest I’ve seen ducted units rated is -5 F. I’ve only really looked at Mitsubishi and Fujitsu. Maybe I’m missing something.


    1. cs55 | | #21

      but for the most part its just from a lack of innovation from companies that make ducted heat pumps.

      the rest of the world has been okay with ductless units and/or makes extensive use out of radiant floor heating.

      energy in the US has been overly cheap/subsidized for decades. so people just use gas furnaces.

    2. Expert Member
      Akos | | #23

      Domestic heat pumps have a lot of catching up to do. The imported ones are rated down to -22F in a lot of cases.

      Your best bet is one of the re-badged units such as the Carrier/Midea or Trane/Mitsubishi

      Something like these:!/product/64684/7/25000///0!/product/69165/7/25000///0

  9. buildzilla | | #24

    this vid summarizes some aspects to consider around the benefits of a ducted system:

    1. maine_tyler | | #27

      Thank you.
      I had seen that video. I'll be honest, the only point I could take away from that video is that ducted systems allow for better filtration. He said a lot of words but that is literally the only takeaway point i could find.

      I think people are operating on entirely different paradigms depending on local norms and expectations. Where I live and grew up, even having a window AC unit was special. Heating duct not unheard of but less common. AC is now becoming more popular, but in large part via ductless cc heat pumps. HRV and ERV are basically unheard of save new high performance builds. Same for whole house dehumidifiers.

      So this concept of needing to circulate, filtrate, and constantly condition air year round comes off as borderline absurd to the uninitiated. People open windows around here. The idea of HVAC running constantly through a summer would seem wasteful to the old mindset.

      So all these benefits of ductwork begin to vanish. But of course winter heating will be more constant.

      I'm not saying the benefits to the paradigm displayed in that video aren't real, im just saying it relies on a lot of assumptions (that people will be running the HVAC nonstop and adding in ERVs, make-up air etc.) which may not hold true to old house renovations in many parts.

      New construction is a different story in that we can rethink old assumptions.

      1. Deleted | | #29


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