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Duct-Free Zone – The Advantages of Mini-Split Heat Pumps

Mitsubishi Hvac Mini Split Heat Pump Carl Green Curmudgeon Seville

mitsubishi hvac mini split heat pump carl green curmudgeon sevilleLast week, (EVER rater and Green Curmudgeon) Carl Seville and I took a trip up to Suwannee, Georgia to visit the Mitsubishi HVAC facility and learn more about their ductless heat pumps. I’ve mentioned here before that 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.

Last week, (EVER rater and Green Curmudgeon) Carl Seville and I took a trip up to Suwannee, Georgia to visit the Mitsubishi HVAC facility and learn more about their ductless heat pumps. I’ve mentioned here before that 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.

Mitsubishi’s line of residential ductless heat pumps is called the Mr. Slim. It’s a split system heat pump, which means that the compressor and condensing coil ductless heat pump condensing unit mr slim hvacare outdoors, and the evaporator coil and blower are indoors. In that regard, it’s like your typical ‘central’ air conditioner or heat pump. You can tell if a house has a mini-split by looking at the outdoor condensing unit (photo right). They’re thinner and smaller than the typical ducted system condensing unit.

The indoor unit can be mounted on a wall, set into the ceiling, or sit on the floor. At the Mitsubishi facility, we saw all three styles, and you can see photos of them below.

ductless heat pump wall mount head hvac

Wall mount (set off from the wall here but mounted flush in a home)

ductless heat pump floor mount head hvac

Floor mount (can be recessed into the wall)

ductless heat pump ceiling cassette head hvac

Ceiling cassette

In addition to coming in smaller sizes (down to 6000 Btu/hour, half the minimum size of regular system), mini-split heat pumps can modulate the amount of heating or cooling through variable refrigerant flow (VRF) to match the actual loads in the house, not just the design loads. They’re also ideal for zoning a house and limiting the amount of energy you use for heating and cooling.

The knock against mini-splits is that some people find them unattractive. They don’t want to have that piece of equipment on their wall, even if it is quiet. Ceiling cassettes are a good alternative. Ducted mini-splits are another, and they allow you to hide the head above a dropped ceiling, for example, and run short ducts for the return and supply air.

Another drawback is that even 6000 Btu/hour is too large for a high performance home that’s going to have several heads (the indoor unit). The reason that Mitsubishi does this seems to be for ease of manufacturing. They make as few different evaporator coil sizes as possible.

Even with these weaknesses, the ductless mini-split heat pump is a great idea and, I believe, will increase in popularity because of the many advantages. There’s a ductless heat pump project in the Pacific Northwest that promotes and tracks the installation of these systems. I heard about this from Bruce Manclark at the recent ACI conference in San Francisco, and he said they’ve got a 98% customer satisfaction rate through about 10,000 installations.

What do you think? Is a ductless mini-split heat pump in your future? Or are you gonna stick with this? Or this? Or this? Or this?

This Post Has 51 Comments

  1. I LOVE Mitsubishi mini-split
    I LOVE Mitsubishi mini-split products! We have been installing them for maybe 15 years or more. Real problem solvers and everyone who has them loves them.  
    For residential use, they are best for bonus spaces, like sunrooms, bonus rooms, finished porches, etc. A home would have to be designed from scratch to go 100% ductless. And, you can get ceiling cassettes for residential Mr Slim products. They also make a ducted model now, *GASP!*  
    Downsides: Installation is critical. If it isn’t installed perfectly, the first time, the system will be nothing but problems. Speaking of problems, they are very challenging to diagnose and repair, despite what Mitsubishi says about advanced on board diagnostics. The average residential service technician will not know even where to start. Additionally, we can have long delays when ordering parts.  
    They are a great product. Amazing technology. A very useful option. I have yet to see a home 100% ductless, but the idea is very appealing.

  2. I agree with your thoughts
    I agree with your thoughts entirely, especially the appearance issue. That why our firm uses their concealed terminal units. In the most simple situations you just hide them in a crawlspace (conditioned of course) or above a dropped ceiling/soffit and attach a short portion of flex duct. More complex situations, like commercial buildings, we run a short trunk with a couple ducts splitting off of it. This might be a pricy option for residential, but it provides people with the concealed look they are used to and as an architect, we appreciate.

  3. Phil:
    Phil: Thanks for sharing your experience with these systems. (And for clearing up my mistake about the ceiling cassettes. I’ll update the article right after I finish writing this comment.) 
    I think that new homes aren’t the only ones that can go ductless, though. My condo, for example, has a central return in the living room and a central trunk running through the lowered ceiling in the hallway, with vents blowing supply air from the trunk. With 32% duct leakage to the outside (mainly to our neighbors upstairs), it’s a good candidate for replacement with mini-splits. You’re definitely right, though, in that it would take careful design to make it work properly. 
    I think some of the drawbacks will be solved as ductless heat pumps become more popular, especially the parts delay. 
    And yes, they do make a ducted model, but it’s nothing like the standard ducted systems. The  
    ‘ductless ducts’ have to be short and straight because they have almost no static pressure to work with (0.2″ water column).

  4. Brad: Yes,
    Brad: Yes, I neglected to mention the ducted head that allows you to conceal it and overcome the appearance problem. I’m hoping they’ll come up with other ways of dealing with this issue, too, like maybe a recessed wall mount unit similar to the ceiling cassette.

  5. I agree with some of your
    I agree with some of your thoughts, however, the inefficiency of HVAC systems in homes is due to the lack of education from the HVAC and building industry, plus some laziness of doing things right and the “build it cheap” mentality. When you make sure HVAC systems are designed, built, installed and commissioned by true professional contractors the right way, you should not have any problem at all, and all systems perform efficiently and economical. 
    I’ve spec minisplits in guest and pool houses or casitas, but they are ugly and intrusive. Manufacturers need to work on their aesthetics to be used at least in midsize or larger homes.

  6. Alison, what options are
    Alison, what options are there for a house in Maine that has radiant heat but no A/C. What are your recommendations for ductless A/C units (in lieu of -old technology- Window units.)

  7. Sorry Allison, I agree w/ you
    Sorry Allison, I agree w/ you. My comment was more about the design, building and HVAC industries about doing things right.  
    With an HVAC system done right, one can control temperature, humidity and ventilation with one high efficient system, plus you can run it at low speed very economically.  
    Another point to make is that to get balanced (or slightly positive pressured) systems and ventilation you should install ERVs or HRVs, which adds to the cost, plus with minisplits is hard to supply all rooms unless you install one or more of them; that could bring affordability and comfort issues.

  8. What’s a ball park cost to
    What’s a ball park cost to run 2 mini-splits, model MSZ-GE09,a in heat mode for 3 hours per day at 67 degree’s F when the outdoor temperature is 50F? I installed 2 units in February and my electric bill increased from $40 per month to $200 per month. My units draw .8amps of current even when they are off-were they installed incorrectly? My electrician says this is normal, I hope not.

  9. Armando: I
    Armando: I wrote something once about the HVAC industry not doing things right. Maybe you saw it already? 
    Yes, there are ways to control temperature, humidity, and ventilation with an HVAC system done right. It’s just not the system that most people get installed in their homes. Most systems are oversized, fixed speed, and have poor distribution efficiencies. Ductless mini-splits are one way to overcome the problems, but they’re certainly not the only solution.

  10. I have been specifying some
    I have been specifying some ductless mini-splits for retro fit work in specific situations. I think they can really do a good job in the right situations. Many houses in the 50 – 70 year old range have multiple additions that were not really thought out or planned well. A 1000 sf house built in 1949 with a crawl and attic. Then a 500 sf add. in 1965 with a slab and flat roof. Then in 1972 a second add with a basement and Master suite of 800 sf. All served by 2 100KBTU/hour 60 AFUE furnaces. No way to go to one furnace. So two of the ductless mini splits? Probably just the ticket. 

  11. Allison, I’ve been given the
    Allison, I’ve been given the opportunity to make the choice and decided against them personally. However, I do recommended them for cottages or similar size structures. 
    However, I have mastered how to design and install traditional split-system HVAC systems. Unfortunately, I have to do the ductwork myself because I can’t afford the price HVAC contractors want to charge me to install it right. I couldn’t trust them anyway. 
    When I apply the principles of Manuals J, S, D, & T, I get a great comfort system I don’t really know is there. 
    The biggest draw back I have with mini-splits is multiple units I have to baby sit. I’m not convinced they last long due to my experience with PTACs. The other reason is that I don’t want to know when my AC system comes on or turns off.

  12. These have been used in Japan
    These have been used in Japan for years. They were used for almost all the air conditioning in homes and offices in Okinawa when I was there in 1996/98. One thing that wasn’t completely clear in your article is that there can be more than one evaporator unit inside the house for a single outdoor compressor/condensor unit. In Okinawa, I saw them installed as a one-for-one in a few places, and three-for-one or four-for-one in other places. The main issue I ever saw there was getting the drain to carry the condensation water outdoors if an evaporator coil was installed somewhere other than an exterior wall.

  13. Allison, I really like this
    Allison, I really like this solution. My only concern is how well would splits really perform in a very cold climate; e.g., several consecutive days below 20 degrees F, with dips approaching zero, assuming the house is otherwise reasonably sealed and insulated? Isn’t it often the case that heat pumps need an auxiliary source of heat when temps get really low? Otherwise, they have my attention…

  14. John N.: I
    John N.: I think mini-splits are a great solution for older houses with additions like you describe. Running even poorly installed flex ducts in them can be a challenge a lot of times. 
    Sam: Why do you think you need to babysit mini-splits? Yes, there are multiple, individually controlled heads, but in a home, you’re probably going to have only one condensing unit for all of them. Also, have you heard how quiet these things are? You’d have to really be paying close attention to notice their on-off cycles. They’re not like noisy PTACs with the compressor sitting in your living room. 
    Lee: Yeah, the rest of the world (not just Japan) uses mini-splits. Sorry if I wasn’t clear about the ability to have multiple heads for each condensing unit. Mitsubishi has models that can take 1, 4, 8, or 50 heads per condenser (and probably other numbers, too). And yes, taking care with the condensate lines is important. 
    John P.: Mini-split heat pumps easily work well down to single digit temperatures with no supplemental heat. They’re more efficient and effective at heating than standard heat pumps, which do require supplemental heat.

  15. These mini-splits are great
    These mini-splits are great and supplemental and space cooling/heating in certain areas. They are very reliable and durable. However, the problem with using them on a 20-story retrofit is that you still need a some kind of DOA system. Most AHJ’s are adopting the new green codes all or in part. The mini-splits do have an OA option, but it is only capable of reaching about 10 feet or 3 meters. Then there is the question of where are going to place the condensor section for the multiple evaporator sections. The ones I have specified will only allow a maximum distance even with over-sized refrigerant lines. If you use these in a cold climate there are only certain manufacturers that design them for below freezing conditions, without supplemental heat. 
    Before you decide to ues only these mini-splits you should thing and design very carefully. 
    I have been designing HVAC systems for everything from restaurants to toxic chemical labs. I am not saying that it cannot be done, you just need to look at the design and the code requirements for OA and look at the economics of this type of design. 

  16. Allison wrote “They’re
    Allison wrote “They’re more efficient and effective at heating than standard heat pumps, which do require supplemental heat.” 
    I agree with first part of sentence, but last part implies ductless mini-split HP’s do not require supplemental heat. That is not the case. It depends on the balance point, just like with standard HP’s. If the mini-split has a higher heat output curve, the balance point will be slightly lower. 
    To John P’s question, there’s no reason not to specify a heat pump (standard or mini) in a cold climate, especially in an area without access to natural gas. See last half of this article: 
    If supplemental heat is needed, it can be provided by electric or hydronic baseboard radiators, depending on relative energy costs and HDD.

  17. David:
    David: Dang, I’ve got to be sharp as a tack with every statement, I make, don’t I? Yes, you’re right that mini-splits don’t completely obviate the need for supplemental heat. But systems with variable refrigerant flow that can provide 100% of the required heating down to single digit temperatures (Fahrenheit) means that in a lot places, they won’t need supplemental heat. I didn’t really mean to say that you never need supplemental heat in any climate or with any system. The devil’s still in the details, as usual. 
    Thanks for keeping me honest, David!

  18. Sorry, didn’t mean to pick
    Sorry, didn’t mean to pick apart your reply. This is an important yet rather technical point that is widely misunderstood. Allow me to explain. 
    Variable refrigerant flow does not increase heat output at colder temperatures. It only allows the system to put out LESS heat at part load conditions. When a variable (inverter driven) heat pump operates at full capacity, all else being equal, the heat output curve is no different than a conventional single speed heat pump. The fact that many mini-splits have higher heat than cooling capacity has more to do with coil design. This raises the output curve, and may give it a slightly less negative slope. I could get a similar capacity bump from a standard heat pump by oversizing the outdoor coil (actually, it’s a bit more complicated than that). 
    Mini-splits, like conventional HP’s, are AHRI rated for full output at 47F. The heat output vs. ODT curve will always have a negative slope. When ODT drops into the single digits, output capacity is less than half the rated output on the models I’m familiar with. BTW, some mini-splits are designed to shut down at a pre-set temperature, for example, 15F, because they don’t (can’t) provide reheat during defrost operation (electric strips would melt the plastic enclosures!) 
    I’m only aware of one heat pump, the Acadia by Hallowell, that can maintain full capacity into the single digits. It has a separate booster compressor. Very different technology. Unfortunately, it’s priced too high to be cost effective.

  19. David, I understand that VRF
    David, I understand that VRF technology is used to lower system capacity at times of lower demand, but isn’t it also how they maintain efficiency levels at lower demand? As I understand it that is it’s raison d’etre. 
    By the way, Hallowell International seems to be defunct. I had some experience with their system, as well as it’s predecessor from Nyle. Wonderful enthusiastic people who, I think, overextended themselves. To be clear, Nyle still exists but I don’t think they produce the residential space conditioner heat pump product any longer. 
    I hope that the concept isn’t allowed to die because of the poor experiences with a company that was probably under capitalized.

  20. Allision, you’re exactly
    Allision, you’re exactly right about how a variable compressor maintains high efficiency at part-load. But this has nothing to do with low-temperature capacity.  
    A heat pump’s maximum output capacity is always a function of outside temperature. The variable drive simply allows the system to reduce its capacity below the maximum. It doesn’t change the fact that output slope is negative.  
    The actual slope and “height” of the output vs temperature curve depends on coil design, not the variable drive.

  21. Sorry, my last comment was
    Sorry, my last comment was intended as a response to what Bill said.  
    Too bad about Hallowell. This is exactly the reason I avoid recommending anything new to clients. There’s simply too much low hanging fruit to be gathered by getting the basics right. Too many people in the ‘green building’ industry are obsessed with chasing the latest and greatest, looking for that silver bullet, while ignoring the elephant in the room.

  22. Thanks to you all for this
    Thanks to you all for this helpful discussion. I am in the process of a deep energy retrofit to an 1884 three family. Each unit is approximately 800 square feet and all will be superinsulated. (4″rigid foam exterior, 3.5″ cellulose interior walls, 6″ rigid foam exterior roof, 6″ cellulose interior as well as R 5 windows and doors and 3″ of closed cell foam on basement floor and walls. I’m baffled by the science and the options when it comes to heating and cooling the units. It seems as though the ductless mini split heat pumps are the least expensive to install….but are they the cheapest to run in a central massachusetts climate with access to natural gas? I have 2 Rinaii space heaters and will have to purchase another and have them installed as back up.(I think)……..or should I just go with a mini split air conditioners only and run a single radiant(baseboard) hot water system for all three units. The units are so small they don’t allow for ducting of forced air units…. Any suggestions? Thanks in advance.

  23. I might add, the above retro
    I might add, the above retro fit is a gut retrofit.

  24. Interesting project, Jeff.
    Interesting project, Jeff. Whether or not heat pumps would cost less to operate ‘above the balance point’ (vs. NG) depends on your marginal electric rate in winter vs. price of NG.  
    Given that you have access to natural gas, baseboard is likely the least cost option for supplemental heat (or primary heat if winter electric rates are high). And as long as you don’t need separate gas bills for each unit, I see no reason to have 3 separate water heaters.  
    One last thought… With those insulation and window specs, your heat loads will be very small. Again, depending on your winter electric rates, supplemental heat demand may be so low that electric baseboards may provide a lower lifecycle cost. 
    This is exactly the sort of analysis I routinely do for clients. The key to a project like this is getting a handle on the design loads, which few people seem to understand. Feel free to contact me through my website for further assistance.

  25. David, Thanks for the reply.
    David, Thanks for the reply. Do you sleep? I guess my question is really… I better off installing a single buderus, baseboard hot water system to handle all three units and a 3 branch ductless air conditioning only unit and spending the extra or should I go with three separate hyper heat models and three Rinai hot air space heaters with an efficiency of 80% as back up. I would naturally have to supply my hot water needs with Rinnai condensing on demand condensing hot water units. It seems as if the buderus system is about 9,000 more then the mitsubishi hyper heat after considering install costs, rebates and incentives. (to the best of my estimation) 
    Thanks again David. I will attempt to contact you to morrow.

  26. Great discussion. Do you have
    Great discussion. Do you have any suggestions for getting the temperature more homogeneous across rooms that don’t have the units in them? We have had some problems getting the temperature right in bathrooms, laundry rooms, and etc. Thanks!

  27. Adam, not all homes are
    Adam, not all homes are candidates for ductless mini-splits. It depends on climate, envelope efficiency and most importantly, room layout. 
    For example, a bath or laundry that has little or no exterior exposure should be fine. A continuous ventilation system (HRV/ERV or exhaust only) plumbed to draw stale air from the baths and laundry will pull conditioned air into these rooms. Whether or not this is adequate to offset the load must be analyzed by the designer, based on an accurate room-by-room load calc. A small amount of electric heat (e.g., in-floor or kick-space) is usually required in full baths. 
    More often than not, bedrooms represent the biggest challenge for ductless systems, especially in cooling dominated climates where the bedroom has south or west exposure. Homeowners don’t want to be told to keep their bedroom doors open at night. On the other hand, putting a head in each bedroom can get crazy expensive. Also keep in mind that the minimum output for a head is usually way to large for a regular size bedroom, leading to wide temperature swings (think about your experiences with hotel rooms).

  28. Does someone have a reference
    Does someone have a reference to the effectiveness of utilitizing exhaust from a HRV/ERV to assist with the air movement in a ductless system?

  29. I’m a home owner in northern
    I’m a home owner in northern NJ. Our house of 3000 square foot, is from the early sixties, California style split level. Exposed wooden ceilings with some insulation, walls same with little opportunity for improvement and lots of windows. We now use oil hot air, inefficient oil furnace and huge ducts through our first floor to heat upper. We initially wanted ground source heatpump, water tubed radiant to eliminate ducts and go green, Way too costly! HVAC contractor adviced 2x Mitsubishi inverter heat pump, ultra high efficiency 4 zone heating and air conditioning system. This would be our only heating/cooling source. I first understood that this is a very efficient system, but reading this blog I wonder if we should do this, as running costs will be absurd. What are your thoughts?

  30. @Miriam, I think Allison
    @Miriam, I think Allison intended to close this article to further comments, given that it’s a year old.  
    In any case, you clearly need professional design assistance from someone other than the folks who sell and install HVAC equipment. Feel free to contact me through my website.

  31. Hello…I recently had a new
    Hello…I recently had a new garage constructed with a 600 sq ft apartment above it. Two rooms plus a bathroom. Spray foam insulation on the ceiling. They installed a 12,000 btu Mitsubishi ducted mini split system. The apartment is shaded and does not get much sun. So far it has been set to 74 degrees but will creep to 78 degrees. Installer swears that it is the correct size. The ducts are not smooth and there are 4 ducts to cool the 624 sq feet. From my research it looks like they should have used smooth ducts with very few bends. They didn’t. The ducts run 15 feet in some cases. Is that too long for this system? I can’t get a straight answer. The contractor is saying that I need to wait for tenants to move in because I am cooling an empty apartment, that’s why it can’t keep up. I’m an idiot with these things, so any help would be appreciated. Oh, one more thing…they said that the system will continuously run unless it is manually turned to “off”. Is that true? Without tenants, my electric bill was $75 more than usual, which seems high for a mini split 16 seer. I dont want to be overly hard on the contractor, but I can’t tell if he is just making stuff up?

  32. Mike, if your mini-split is
    Mike, if your mini-split is the Mr. Slim SEZ-KD12 (as opposed to a commercial city-multi), then no, it cannot support the duct system you described. Not even close.  
    Mitsubishi stipulates a maximum of 0.2″ external static pressure for the above referenced ducted air handler. That’s very difficult to achieve unless the designer really knows what he’s doing. 
    You can hire an independent technician to do a simple static pressure test (takes 10 minutes), which may give you leverage to deal with the contractor. However, given the run-out lengths you mentioned, even smooth (metal) ducts would likely exceed the system’s air delivery capacity.  
    The blower can be set to operate continuously or on cooling calls, but the outdoor unit definitely should cycle off when the temperature setting is reached.  
    I suspect you may have insulation and thermal bypass issues. You mentioned foam on the ceiling, but that’s just part of the picture. 
    Contact me or Allison privately if you need more assistance, as this is getting to specific for a blog.

  33. We have a 160 plus year old
    We have a 160 plus year old home – all brick – an antebellum. We have no duct work, of course, and have investigated the Mr. Slim’s which we like. However, we are shocked at the price quotes we are receiving, especially when compared to online prices. Any advice is appreciated. Why is the installation cost so extremely high??? 

  34. We have a 1200ft smie
    We have a 1200ft smie detached home and are thinking of having a mini ductlesss system installed. We curently use electric baseboard heaters during the winter and window installed AC units. We also have a HRV which supplies air circulation to our main floor as well as our basement which we will be finishing soon. Could you give me some advice as to whether or not we should go with a unit for just AC as I would have the basement level one operate as a dehumidifier in summer or a unit that gives us Heat/ Ac. Our winter temps reach a low of -35 C. Thanks for any info…Cheryl

  35. @Tim & Mary, you
    @Tim & Mary, you could get prices from a few more dealers, but the issue you raise is common. I’ve advised several friends buy through the internet and install it themselves, and pay a licensed contractor to make the refrigerant connections and commission the unit. For a couple of hours of work, you might have to pay $300 or so. Of course, don’t expect them to warrant the unit. 
    The smaller units plug into a standard AC 120V outlet (indoor unit), with the outdoor unit drawing power from the indoor unit. You just have to provide a level surface to support the outdoor unit and cut a hole in your wall for the refrigerant lines. If you need to a new electrical circuit, you should sub that out to a licensed electrical contractor unless you’re qualified to do electrical work. 
    @Cheryl, heat pumps (heat / AC) units don’t cost much more than AC only. No matter how cold your area gets, there are more heating hours above freezing than below, so you should take advantage of the *much* lower operating cost of the heat pump vs electric baseboard. Just make sure you keep the baseboard heat off until the heat pump needs some help, and then keep them on the lowest setting that will maintain the space at the preferred temperature. The more heat the baseboard contributes to the mix, the less you will save. For your climate, I recommend Mitsubishi Mr. Slim H2i Hyper Heat (MSZ-FExx indoor unit, MUZ-FExx outdoor unit). At present, H2i Hyper-Heat performance is only available in single zone configuration. If you need more than one indoor unit, a multi-zone system night be less expensive (MXZ outdoor unit with inverter technology)

  36. I have a 100+ year old home
    I have a 100+ year old home in central GA, 2250sq. ft., that I would like to install minisplits in. I don’t mind installing one or more units to accomplish what this. The master bed/bath is approx. 500 sq. ft. and I was thinking about one small unit for that. Then a dual unit for the other two bedrooms, each about 150 sq. ft. That would leave the living room and dining room….each with 12 ft. ceilings, kitchen, sunroom and laundry room for maybe a third unit. Any thoughts?

  37. @Carl, there’s no way to know
    @Carl, there’s no way to know whether this would be a reasonable solution without knowing a lot more about your home. In particular, how it’s currently heated/cooled, if windows are dual pane, how well it’s insulated, etc. The fact that it’s 100 years old leaves too much to the imagination!  
    You can contact me privately for further advice.

  38. I need to install some kind
    I need to install some kind of heat in a home I recently purchased. It had a gravity wall furnace that the inspector said was unsafe so I had it removed. The house is approx. 1000 sqft. Its 2bdrm, 1 bath . Old original windows and about 6 inches of insulation in the attic. OH I’m located in Los Angeles about 2 miles from the Pacific Ocean highs in the summer around 82 and winter lows at night of maybe low 40’s (maybe 30 nights a year). I don’t need much and I’m thinking of a ductless mini split like the mitsubishi or a central gas furnace laying on its side in the attic. My main concern is the cost of electricity to heat vs. natuarl gas. Is there a way to compare the two?

  39. @Steve, mini-split vs gas
    @Steve, mini-split vs gas would normally be a simple conversion based on relative equipment efficiencies and energy costs. The hard part is estimating the supplemental heat fraction. But in your case, supplemental heat shouldn’t be required. 
    The problem in your case is determining the applicable electric rate (e.g., marginal winter rate based on temperature zone and usage profile). Unfortunately, electric tariffs in California are notoriously complicated. And if you live in the LADWP service territory, a large two-step rate increase is pending. 
    Contact me privately through my website if you’d like help selecting the best system for your situation, perhaps avoiding an expensive mistake.

  40. I am remodeling a small
    I am remodeling a small apartment for my daughter’s college years. It is at the top level of a three-story building, Spancrete floors and ceilings. It still has the original Lennox air handler, manufactured in September 1969. Amazingly enough, it’s still working fine. However, given the age, everyone, including Lennox, is recommending I replace the furnace. I would like to drop the heating element to about 8 KW, but Lennox would not release the drawings for the heating element I need (they no longer make the part for my 43 year old air handler). The reason I want to reduce the heating element is because I am installing an electric tankless water heater and I am limited to a total of 125 Amps for the entire apartment. 
    Intuitively I could adapt a Goodman 8 kW heating element to use it in my 43 year old air handler. Or, I could replace everything with a new system. If I go with a new system, I am considering a Mitsubishi Mr. Slim. Would the heat pump provide heat in a typical northern Illinois winter? Is a drain required with every wall unit? Is there an application similar to Mr. Slim that would fit into a duct system? Should I replace my 43 year old Lennox with a “classic” air handler coupled with a new compressor on the roof, given the ducts already in place?

  41. thank you for help me made my
    thank you for help me made my project work in collage.

  42. Michael, I would have
    Michael, I would have commented sooner but didn’t receive a notification when you posted (for some reason, notices on this blog can be delayed by weeks or even months!) 
    I love to hear about systems that last for decades! But you really should replace the air handler so you can get one with an ECM motor, which will consume much less energy than a standard motor. 
    Also, sounds like the current system is an electric furnace. If so, you should insteall a heat pump (outdoor unit) instead of replacing the air conditioner. A heat pump only costs a few hundred extra and will consume less than a third as much energy as an electric furnace. I recommend a nominal 14 or 15 SEER single stage model, which when combined with an ECM air handler, will yield 15 to 16 SEER (cooling mode). 
    No heat pump is going to handle the entire heating load in that climate (except perhaps for a Passive House). The heat pump air handler can be outfitted with electric elements (like your existing furnace). The elements will only operate as needed to supplement the heat pump as required, so 8kW should be more than enough for an apartment, perhaps even 5kW (would require a load calc). 
    Ductless heat pumps don’t have supplemental heat, so if you go that route, portable heaters (or electric baseboard) would be needed in mid-winter when the mini-split can’t keep up with the heat loss.

  43. We have no heat/ac in our
    We have no heat/ac in our 1500 SQ FT home in Central Texas (Hot). We just purchased this home this year and I intended on installing central heat/air. Then I realized there isn’t any attic space. So I thought about using a duct system through the floor. Then I heard about the mini split.  
    I think I need a 3 zone system, but I am not sure. We have a pretty open floor plan, with 1 spare bedroom right off the living room. The house is old, and isn’t insulated very well. Any thoughts?

  44. My family recently retired to
    My family recently retired to Nicaragua, and have purchased and renovated a beautiful 2000 sq ft. home. They are not looking to run the machine constantly, but just to take the edge off. I am looking for suggestions on a larger unit that can stand some humidity. Any thoughts here?

  45. I have 3 Hyper heat Mr Slim
    I have 3 Hyper heat Mr Slim units in my Mobile home 1979. 
    I only went with 3 units because I don’t heat the 2 ends much as much as the rest of the house and the cost difference was very little. and also wanted the -13 degree Heat pumps with no need for backup heating. In fact I took out the 2000$ a year heating oil furnace. This winter with temps down to -2 degrees my highest  
    bill was 94$ Yes they are not as pretty as normal unit but saving over 1000$ a year I can live with that. As far as the sound I can hear my next door Hugh 18000 BTU unit all the way over here and can only hear mine on start ups when I need a loot of heat or Air and that only lasts 15 Minutes or so. 
    Best HVAC I have ever used.

  46. I am getting different advice
    I am getting different advice from different installers. Any help as to which installer(s) are correct would be appreciated. 
    All installers recommend the Fujitsu mini ductless systems for both heating and cooling. Here are some of the differing opinions: (1)using the multi-zone systems, i.e., two or more indoor units for one outdoor unit reduces the efficiency; as a result, this installer recommends a 1:1 indoor/outdoor unit systems, which greatly increases costs; (2) the ceiling cassettes are mainly for commercial purposes and are noisy and has problems with draining the condensate, which may lead to eventual problems in the ceiling; (3) using one indoor unit for two bedrooms, even with the doors open; the doors of the two bedrooms are at a ninety degree angle to each other, so the louvers cannot be directed to blow air out from one bedroom directly into the other.

  47. @Roy, all are correct to some
    @Roy, all are correct to some extent…  
    (1) multi-zone systems are indeed less efficient than single zone (as are ducted mini’s, and larger capacity systems).  
    I’m not sure I’d agree that 1:1 “greatly” increases cost. Keep in mind that you don’t need (or want) a head in every room!! The minimum output of even the smallest 1:1 system is way larger than the typical bedroom load. Gross over-sizing reduces or eliminates the benefits of variable compressor capacity and can lead to comfort problems (what I refer to as motel room syndrome).  
    (2) True that ceiling cassettes are not typically used in residential. I can’t speak to the noise issue, but condensate shouldn’t be a problem if installed correctly. You can have condensate drain problems on any AC system if improperly installed! 
    (3) If you live in a cooling dominated climate, especially if any bedrooms have south or west exposure, ductless isn’t a good option. Even in homes built to Passive House standards, glazing loads require direct supply air.  
    I sometimes specify ducted mini’s for bedrooms in super insulated homes, but blower power is very limited on most models so a low-friction duct system is critical. 
    For a super insulated home in a heating dominated climate with little or no cooling load, a centrally located ductless unit may work well since most folks don’t mind cool bedrooms. 
    In general, climate, home layout and envelope, and homeowner expectations are key factors in whether ductless is an appropriate solution.

  48. We have a 3500 sf home in
    We have a 3500 sf home in Northern CA which is serviced by two central systems. Downstairs works great, but the upstairs only cools the bedrooms sufficiently. There is a family room over garage which was former attic space which is ducted, but never conditioned sufficiently. We are thinking that mini-split is our answer. The area is a very long rectangle (40’X12-15′)with a stairway about 2/3 back from the front side of the room. There are windows on front and back ends..  
    We had a contractor take a look and he is talking about either three evaporators with a 36k system or a ducted system with duct runs up to 20 ft. I’m worried that this might be grossly over sized for the space. After reading through the posts and taking into consideration the openness of the space, could we get away with a single evaporator placed centrally on the long exterior wall (west wall)? I don’t want the “hotel feel” (wildly varying temps) that was spoken about in previous posts.  
    Thank you for any tips you can give. Our summer high can be 109 and lows seldom venture below the 20’s.  
    Would ductless be a good solution for this area? And does a single evaporator have the wind-power to get the cooling throughout this open space? 
    Thanks in advance.

  49. @Ruth, cooling rooms over a
    @Ruth, cooling rooms over a garage (bonus rooms) are often problematic for a variety of reasons. It’s always best to diagnose the the problem before throwing money into more cooling capacity. For example, if the room has insulated knee-walls, the stud cavities should be encapsulated on all six sides (top/bottom/left/right/front/back), otherwise, the R-value of insulation would be greatly compromised.  
    In any case, there’s no way to assess your situation with the information provided, or in a public forum like this.

  50. I wanted to comment on the
    I wanted to comment on the noise mentioned that a cassette style can produce. In my case, I have two Mitsubishi cassette style units that were recently installed into my renovation.  
    They are indeed noisy. I am currently researching this myself since it seems too odd to be operating correctly. This only occurs in the air conditioning mode and not while heating. My air conditioning company said that this is due to the variable speed DC motor that pumps the water out. The electric eye is basically seeing some, but not enough water to pump it out and is running in a consistent state of trying to purge water.  
    The units cool and heat great and you can barely notice the mount in the ceiling. The draw backs are the following: There is no circulation of fresh air and there is basically no useful dust filtering. I can deal with these in other ways, but the noise that these units are currently producing makes me nuts. It’s like a white noise machine that never stops. Both units do it, so it’s consistent.  
    I think this can be fixed if I got anyone to donate some know how. That is the other thing I found… at least in my area (Austin Texas) there is a general lack of quality technicians.  

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