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.

We also have a dual fuel HP in ATL (13 SEER + 80% NG furnace). If you're going to invest that kind of $$ in a new system, plus pay to operate it for the foreseeable future, I'd do everything I can to ensure I got a quality install. Below is a link to a Southface Energy Institute fact sheet on blower door and duct blaster tests. They're an ATL non-profit. I highly recommend the info they have on their site. They might even be able to help or point you in the direction of a contractor to design your system and/or test your house/ducts. Ideally, you'd have the blower door done to feed into the Manual J sizing of the system. Then, after your new ducts were installed and sealed (but before insulating), you'd have the latter done to test how tight the duct system is. A brand new system, installed right, ought to leak at about 0.05cfm/sq ft of living space. That's only 125 cfm for your house. If at all possible, you want to maximize the amount of rigid ductwork, only allowing flex duct at the runouts (I'd get at least the Vision Pro w/ an outdoor sensor to control the switch to Aux heat. My understanding is that the IAQ version will handle the staging possibilities better than the 8000 series VP. It also costs more. I'd also be interested in getting a HP w/ good low temperature performance. Our gas bills have gotten smaller since getting the VP set up to control the switch. But on an old house, you're still going to use gas for the days in the teens/twenties like we've seen this winter. Anyway, food for thought. We have used ACS to do work on our system. They sell Carrier equipment. Here is a link that might be useful: Southface on blower doors and duct blaster testing

Thank you for the prompt reviews! Looks like Proposal #1 is the winner so far. Mike ��" the attic fan made a huge difference in second floor comfort. One of the best things I did. Glad your experience was the same. I will look into the 2 stage AC. I will not run the fan or put in an extra return for the humidity/temperature change issues. I will just continue to use my dehumidifiers. They do take care of the issue. I am going to plan on replacing the line set ��" it is easy to get to. What do you think about the drain pan/wet switch that will shut off the AC if there is a leak? Is it going to go off over nothing like a smoke detector I used to have and drive me nuts? Or is it a good idea? I might not have been clear about one thing. Both contractors told me to keep the old air filter set up (Spaceguard High Efficiency). It is the old Aprilaire humidifier that Contractor #1 said replace due to age/parts and Contractor #2 said keep it, parts are not going to be a problem and the only part that goes bad is the solenoid. Keep the old one or buy a new one? Contractor #1 is going to look into the Carrier early failure of heat exchangers settlement. It might only apply to the secondary heat exchanger. The primary one failed on my furnace. I meet with the last contractor tomorrow. I hope to have all the bids by the end of the week. My goal is all new equipment before I have to turn on the heat!

Johnax, I think we already covered your misinformation/mischaracterization in a previous post. PVC flue, instead of metal, is a huge plus. The option to sidewall vent is also a huge plus. The potential for eliminating a roof protrusion is a big plus. The potential for fixing venting problems in old masonry flues without lining them is also a big problem solver. There are millions of 90% furnaces out there since the 1980's... it's proven technology. If anything, I have found through my experience that it is the 80% furnaces that actually have the corrosion problem. I don't know about natural gas prices being cheap... what I know is that all energy - oil, gas, electricity is interchangeable to a great degree and therefore the prices are linked in the longer term. In other words, there may be short-term market fluctuations, but the price of all forms of energy are connected. We have seen significant price increases in natural gas in the last several years, I'd expect to see significantly more increases - esp if any type of cap and trade policy is put in place. The only down side I see with the OP's situation is that he evidently doesn't have a floor drain available and would require a condensate pump. Not a big deal - they are $50. Giving up a 15% efficiency gain - for less cost after the tax credit-- doesn't make any sense to me.