OMG, reading this makes me so glad that I don't have ducts in my crawlspace anymore. Here are some of my previously-posted thoughts. I wish I had more time to edit it. I hope it is at least marginally understandable. ------- A couple of things to keep in mind that are often left out by marketers and sellers. Most mini spits don't have back-up heat so you will not have any heat while they are defrosting. (I think I ran across at least one brand that does.) So far, the only time I find it annoying is in the morning when I want things to be warming up fastest. Otherwise, I don't really notice it. I know that with Mitsubishi's current residential equipment, the 1:1 systems have better low temp performance than the multi-splits. They are more efficient too. Even if they do have back-up heat, you can kill the efficiency pretty fast if you need back-up very often. Keep in mind that there are alternatives to the wall-hung indoor units. They cost more, but there are units that can be dropped into ceilings and others that sit on the floor. There are also short, ducted units that would solve that big room problem by splitting the supply and return. Condensate needs to be dealt with using pumps. I have 7 of the old-fashioned wall units. The only place I would change in my house is the dining room. It is a small room and it is obtrusive there. I should have used a ceiling cassette in there. They do cost more and are less efficient. What mini splits might not work well for is conditioning a bathroom. For that you might need one of the short ducted units to handle one room and a bathroom. Unfortunately, that will add a lot of cost. Ceiling cassettes or small air handlers might have been less expensive to install than wall units despite the equipment cost in a couple of rooms. I thought of this when my system installation was well underway, unfortunately. The reason might be unique to my house. Since we were abandoning a duct that ran through a chase in the middle of the house, and the condensate lines that also ran through the chase, we could have very easily routed the refrigeration lines, drain lines and control/power cables through that chase for several rooms rather than going through walls and under the house. It would have required condensate pumps, but that is a relatively minor issue. This kind of thing is where installer experience is likely to be a factor. Installing a mini-split through outside walls, as is it usually promoted, is pretty quick and straightforward (Read fast and cheap straight through the exterior walls.) compared to installing a new duct system in an existing house with no central AC. My install was done through interior walls running the lines/cables under the raised house and out to the side which was much more complicated. If I were doing this over and I had a good duct system within a house envelope, I might stick with it to save money. The trouble is, what is a good duct system? More often than not, they are outside of the living space in older homes. In addition, they are considered good when they leak 5% of the air and they only get worse as they age. Even if the whole duct system is within the envelope, you will still get pressure differentials that can force air in or out of the house. Summary of the factors that went into my decision: I had a crappy duct system. My system was in the attic with parts of the duct system in the attic and a trunk that was a furred-down space over the main hallway. That space was both in and out of the conditioned space. The worst part was one duct that started at the AH in the attic, dropped down under the house in a chase and ran for about 30 feet before it reached the first floor register in an addition with a flat roof (thus no attic). It then reduced in size and ran another 25 feet under the house. That part might have been mini-splitted even if the rest of the house retained a ducted system. Mini split sellers market their good dehumidification heavily. The variable-speed-blowers and variable speed compressors would help with low-load situations better and single-speed equipment. I am sure that some variable-speed ducted systems can match it. In my climate, if you have a lot of air infiltration, you will have a humidity problem no matter what you install. No matter how good at dehumidification any cooling system is, in my climate (US, Gulf of Mexico coast) a dehumidifier is a very nice thing to have for a few weeks out of every year. If you go mini splits, don't mount a wall unit above where you will have a bed. I saw advertising that showed that and planned that. I changed my mind figuring that at low speed, at night the cold air would sort of cascade down over the heads and be uncomfortable. I am glad that I changed my mind about it. I don't know if that cooling-mode problem would occur. What I did find, since we did the installation during heating season, is that the default programming of the heat pump mode makes the units good ceiling heaters. As they approach the set point the blower speed goes way down so hot air gets stratified near the ceiling even though the louvers are pointed down. Setting the blower speed manually to a slightly higher speed fixed that. A ceiling paddle fan would too. Putting the indoor units above the bed would have been uncomfortable if only for that reason, hot air right in the face. As far as efficiency goes, my worst of my three "systems" is supposed to operate at SEER 17.5, and HSPF 8.9. The 1:1 systems are rated better, some over SEER 20. Obviously, I do not have to subtract duct losses from that. I appreciate the ability to put ducts within the house envelope, but you can still get pressure differentials from room to room that push air out and suck it into the house. My house is a 1940 raised, wood-frame house that probably could have been built in 1920 for the construction techniques. It must have been conservative builder. It is notable that the house still has all the doors and walls that it ever did. (I have none of that open floor plan nonsense. If I am going to stay married, I need to be able to get away from my wife sometimes and she needs doors to slam when she gets mad at me.) We only seriously heat or cool rooms that we will be in. We are not home much either, and we are working in the kitchen a lot when home. The life style has a lot to do with our decision. Minisplits are inherently zoned and our house lay-out is such that we can take advantage of that. I have found the remote controls of the Mitsubishi not very flexible. You can set on and off times, but you can not really make true setbacks. You might want to check the possibility of hard-wired controls and investigate closely how the remotes work for several brands. One thing you might want to keep in mind. As of 2011, I can say that the Mitsu (and perhaps all brand) multis are less efficient than the 1:1 units and they do not do as well as the single units with heating at low temperatures. For the former, I think it stems from the fact that the compressors only throttle back to a certain percentage of max. For example, a single unit might be rated at 9000 BTU. If you only need a little cooling, and assume that they throttle back to 10%, you can efficiently get 900 btu out of them running constantly with no on/off. If a tri unit is probably 22,000 btu and can throttle back to 2200 btu with the same assumption so your compressor will be flicking on and off more often which yields poorer humidity control and not as even cooling as you might expect from looking at data from the single units. This might affect planning an install of a system. If you are going to have one single unit in addition to several multis, you might consider putting the single where it will be operating at low load a lot, like a bedroom. I have some interesting data in some service manuals that I was able to download that shows, a little indirectly, what the lowest capacity is that they will run at.

Where milder/less mild matters is in the heating season with a heat pump. The AC functions about the same, but if it's too cold out the heat pump BTU output may not be enough to keep up. Even if you have plenty of AC capacity in the summer. I assume you're on NG and not propane. Also, $2.1 per hundred cubic feet (ccf) would be more normal. Ours in ATL is around $1/therm (therm = ccf), and it might be $2.1 once you add on the administrative costs. It might make sense, if you're already paying the overhead on your NG account, to go with a dual fuel system. The extra use spreads that admin cost further, if your system is set up to do it when it makes sense. A dual fuel system will run the HP until it can't keep up (or the controls lock it out based on outside temperature), then kick on the gas furnace as the 2nd stage. This takes advantage of running the heat pump most of the time without needing electric heating strips as backup heat. The HP will put out about 3X as much heat as the energy it uses- that's what makes it cheaper to run than a NG furnace. But the backup heat strips are 1:1 on energy to heat, which usually isn't competitive with NG. Also, I kind of like the idea of having a standard efficiency gas water heater. Offends my drive for efficiency, but as a kid on the N end of AL, the power went out enough during hurricanes, ice storms and the like that it was nice to still have hot water (and a fireplace) when that stuff happened.

All units are Bryant Furnace = 355BAV A/C = 127A Heat Pump = 226A Had to order today to take advantage of rebate offer that ends 8/31. Never could figure out how to estimate the cost of running the heat pump vs. the gas furnace and couldn't locate any on-line calculators/spreadsheets that would help. Figured I'd save a bunch with new 95% furnace over the old sigle-stage 80%, and the new 17 SEER a/c over the old single-stage 10. It's small house (1450 sf) and well insulated, and I didn't know if I'd squeeze enough additional savings with a heat pump to justify the extra initial cost of the pump plus whatever extra cost would be involved in replacing it sooner because of running it much more. When in doubt, play conservatively (at least where money is involved), so I went for the a/c unit. Wish I'd discovered this website a month earlier. Thanks to all those who responded.

Hi, I'm in the midwest and have a 5100 sq ft home. I'm looking at replacing my 17 yo furnaces, 2 Carrier Weathermaker high efficiency , with electronic filtering system , (eletroair SST), two air conditioning units, one blown and one 4 years old (got 10 years out of the blown one) with a similar set up to above. Recommended by the dealer is 1 American standard 16, 2ton communicating heat pump with a Am ST. Freedom 95 60K btu, 3 stage furnace and Acculink 900 comfort controller... AND 1 Heritage 16, 3 ton communicating heat pump with Freedom 95, 80K btu, 3 stage furnace, both with the AccuClear air cleaner system. We could keep the 4 yo air conditioner for a while, and put in the extra heat pump later. We could keep the current air cleaner (the kids, who sleep near it downstairs say it cracks and pops a bit). I'm looking at getting another quote, and from the looks of it above Carrier would be the place to get another quote and opinion. The American standard dealer made a big deal about the communication between the furnace and heat pump, calling this "geothermal above ground, at 1/3 of the price". We probably could get a couple more years out of our furnace, but has needed repair a couple of times, and were told it could become a problem, which we'd like to avoid in the middle of winter. We did consider geothermal and priced that out last year, and just felt the retrofit wasn't worth the bother. A contractor friend recommended that future high efficiency furnaces would make the geothermal unnecessary, at least for retrofitting. Any opinions out there?