They've GOT to be better than window/wall units, plus no ducts running through HOT attics, dropping your laboratory-measured 16 SEER to a real-life 11. ;') OTOH, though the condenser+compressor are now outdoors, you still have fundamental issue with the warm return-air and the cool outflow-air being co-located... but, apparently this problem has been engineered away to a significant degree. It is very difficult to find someone who is NOT happy with their "mini-splits", though correct sizing and installation are still paramount... as is patching up the huge holes left by the window units. ;') I wonder if Brickeyee could provide the details on how his noisy units are MOUNTED in his industrial setting, i.e. perhaps on exposed metal studs, uni-struts, or some similarn base that does not dampen vibration? One does not hear the noise complaints from residential users.

Thanks for your help, zL700; I like your link for SlimDuct enclosure, much better than my idea for 3"-4" pvc pipe! I plead guilty to a LOT of sharing! Once one reads all the way to the end, my question in the first line was 'history' : "Can anyone support my argument that it is ample to use a dual split unit for just the front two bedroom's? " This would save both cost and a difficult condenser install location. In short: We have a MrSlim MSZ-A17NA single-split 17 Kbtu unit for the 3rd floor finished attic, and a conventional 28 Kbtu ducted unit on the first floor. Our calculated 50 degree day heat loss for the entire house is 48 Kbtu, of which the two rear small bedrooms are only 5 Kbtu each. I have agreed to put in a dual-split 9+9 or 12+12 for the two 2nd floor front bedrooms. Shouldn't this effectively cool the entire 2nd floor? I need technical, experienced opinion to support my desire to avoid having to put in a 3rd condenser in the larger of the two rear bedrooms. Thanks to All - - Old Salt Details were dated SEP 3, 2307 hours.

I have no experience with heat pumps in an area that cold. I understand that they are getting better all the time, but I don't know how they will do in your coldest weather. Cost will depend a lot on how many rooms you have. If it is an open floor plan, cost will be lower. If you have lots of walls and doors, the cost will go up as the number of units increase. Ducts are bad when they are outside of the house envelope. Design your house with indoor ducts if you go that way. Ducts are bad when returns are inadequate causing pressure differentials between rooms. This, just like leaks in outdoor ducts makes an air handler into a power vent. Mini splits are inherently zoned, but what does that get you? Zoning is not going to save you that much energy with a well-insulated house. Heat transfer between rooms will be much faster than from inside to outside. Zoning for comfort and control might be worth it. I have seven mini splits inside on three systems for nearly 5 years. I live in a hot, humid environment in a home that was retrofitted with central and had ducts in the attic and crawl space. The original central system was done right with a dropped ceiling (9 to 8 foot) in the central hallway. Later is was messed up with outdoor ducts added. The mini splits perform beautifully for humidity control. Maintenance is higher with mini splits. At minimum, you need to clean filters for each unit instead of one, two or three. I am finding that maintenance of my Mitsubishi units is greater than that. Lots of dust gets stuck in the "coils" despite regular cleaning of the filters. The back side of the coils is difficult to reach if the units are near the ceiling. In addition to that, the blower cages get dirty as well. I am trying to figure out how to get the cages out to clean them without largely dissembling the whole thing. There are some characteristics of mini splits that some to not think of. Their performance measures are hard to compare to single speed central systems. My understanding is that they are locked into a constant chosen frequency (speed) and measured like that. In real operation, at low output, variable speed systems are more efficient than at high output. This can be a factor in choosing to use set backs, which can be counterproductive. My belief is that the manufacturers could fix that by allowing a set back recovery at less than 100% output with more sophisticated controls. My mini splits run very well on portable generator power. There is no start-up surge as seen with on-off units. They spool up very smoothly and slowly. If you have more than one system, you will never be totally out of heating or cooling. You might find this study useful. It was an eye-opener for me: Long-Term Monitoring of Mini-Split Ductless Heat Pumps in the Northeast Building America Report - 1407 December 2014 Kohta Ueno and Honorata Loomis

Just realize that if you are spending a lot of time in a room that is far from a thermostat, the thermostat in this case is not a telepathic device. It's impossible to control temperature in a room that is not designed to be operated in the way in which you are operating it. Moving the thermostat to this room adding ducts won't solve the problem either. In some cases single floor homes can be improved with zone system control. But this is a dangerous statement, zone systems are science and 'art'. There is a plethora of garbage and much more in terms of people who actually understand how to do these thing properly. With that said, a HVAC zoned system will not fix and otherwise ailing system. It needs to be an elegant solution otherwise it will be a waste that will cost you many different ways. It's not a bad idea to start doing your research and find out who the 'most knowledgeable' HVAC company is in your area. I think Alabama climate is probably more on the humid side than dry side so if you look into systems that better handle dehumidification (typical 2 stage AC, even better is inverter AC) if you pair that with a properly installed zone system I think you will reach your heating and cooling bliss moment. Also when selecting a company select one not only for knowledge but also service after the sale. Once the sale is over, you want to be sure you can get the service you require to fix any problems that develop with the new system. Things like availability. Are they open 8-5 and closed on the weekends? Do they show up on time? Constantly busy and don't answer the phone or return your calls? Where there is smoke, fire is usually not far behind. If you know what I mean...