There have been some threads on the Heating and Air Conditioning forum about these types of systems. Perhaps someone there would be able to answer your question.

I have a 60s ranch with hot water heating, so I follow the info about these systems. Right now we use room air conditioners but someday maybe we'll upgrade.

cocooner

Thanks for the advice. I suppose I should have mentioned that the rooms in question each have two "quarter-round" windows at one end of the room, and a skylight. A window unit is out of the question. I thought briefly about installing a window unit through the wall, but the neighborhood planning committee would be on me like a duck on a June bug!

The multi-duct requirement sure is a show-stopper, though! If I go for a Unico or Spacepak, I guess it should be sized for the whole house, instead of as an auxiliary system.

you should also consider a mini-split, which has a compressor on the outside, but a blower on the inside (basically mounted on an exterior wall). The two are connected by a small copper tube and a small drain pipe, and the compressor can be mounted on the roof or on the ground.

LG and Mitsubishi make good units.

Here is a link that might be useful: mitsubishi mr. slim

I am going for the mini splits in my addition (one in kitchen, one for bedroom, compressor outside), because I can't afford the spacepak/unico systems for the whole house, we currently have hot water radiators. They aren't cheap but are a good in-between from window unit to high velocity systems. If you are just cooling the attic, I definitely recommend this solution.

We do have forced air heat, so we're having a 48,000 BTU central air system put in, which isn't going to do much for the third floor. However, we won't use the third floor much, so I think a potential save will be a portable AC, for use when someone is in residence up top.

Here is a link that might be useful: Portable air conditioners

We had a Unico system installed several years ago. Conventional A/C upstairs, but Unico downstairs. The only place in the house where the blower units would fit was in the loft. The installers made a tremendous mess of the heavy fibreglas attic insulation I had laid down myself about 10 years earlier.

Overall, I have mixed opinions about the Unico system, even though we had limited options for getting central A/C downstairs because of lack of space for conventional size ductwork. Most of the Unico ductwork runs under the house in the crawlspace. Convetional ductwork might just barely fit, but would have severely restricted cross ventilation in the crawlspace under the house, which was already inherently prone to moisture problems.

My main complaint is that the flexible plastic ductwork is not leakproof. With the high pressure, it only takes a tiny pinhole in the plastic to create a leak where you can feel the air blowing out. The way the flexible tubing fits together allows additional air to escape. I'm not sure if it is the inherent design of the system or if it was installed improperly, but the ductwork leaks at several of the joints. I am glad we didn't have the mini-ducts run in the walls between studs as the Unico ads show, since I have had enough trouble with the ductwork that having them inaccesible would have posed a major problem.

Another problem is moisture condensation on the outside of the ducts, especially where they run under the house. It gets very humid here in the summer, and despite the fibreglas insulation surrounding the ducts, they sweat to the point that you can actually see water dripping off. Another reason I am glad we don't have any ducts running inside the walls is that the condensation would have undoubtedly eventually caused water damage to the wooden framing structure of the house.

Just a week ago, the system stopped cooling. The units still ran, but there was very little pressure to the air coming out of the vents and the coolest we could get was about 85 degrees. I went under the house and discovered that the galvanised steel bands used to hold up the main central duct that feeds all the little ones, had rusted in two and the whole thing had dropped onto the ground, and the large rigid steel part had actually separated from the main flexible plastic section coming down from the blower unit. The reason the system was working so poorly was that most of the cool air was blowing out into the crawl space!! Instead of calling for service I repaired it myself, replacing all the original steel bands with plastic ones, using stainless steel screws to hold them up. (I suspect a commercial repair service would have replaced all the rusted out hardware with the same kind of rubbish that was used originally.) Fortunately I was able to repair the separated ductwork using heavy duty professional grade duct tape, the stuff that is actually designed to be used on HVAC systems.

I think if we had known all about the Unico system that we know now, we would have chosen something else. The ductwork is failure prone, leaks air, and has the potential for causing damage to the house due to moisture condensation.

"The way the flexible tubing fits together allows additional air to escape. I'm not sure if it is the inherent design of the system or if it was installed improperly,..."

Improper installation. Period. Incompetant would be a good description. There should be no holes in the outer jacket. Period. None.
Steel straps are just plain stupid for this work. Nylon mesh in 3 inch rolls is cheap and handy. Aluminum staples should be used to prevent corrosion.

I have a Unico system installed by the prior owners in my circa 1970's colonial. It works rather well, the house cools mostly evenly (2 blowers, 1 in basement and 1 in attic) connected to 2 A/Cs outside. The blowers are not whisper-quiet, but I am used to old, in-the-window A/Cs that would wake you up at night. I think the amount of noise in a high velocity system is due to how well the installers did in snaking the vents. Also, I have retaped some of the tubing in the basement where I have felt some air escaping. It's important to use that sticky foil tape, NOT duct tape, which will provide a better seal (not sure where I picked up that factoid).

My question is, do you need to have it serviced every year? This is the first year in three years I have not had it serviced, that is, I have not had a tech come to the house and look at each air handler.

Besides, what does a tech do to service it? When I was home, the tech asked to fill a gallon milk jug with water, which I assume was to clean the coils. Is this something I can do myself? The Unico website is not very descriptive on how to maintain the system. I do change out the filters every year and I would like to not pay $80 each season if they just clean the coils.

If there is a duct up in the attic which puts cool air up there - would some strategically placed fans move it around? Or is the issue not enough cool air period?
Is there any way to put in some more roof ventilation to keep the attic from heating up as much - thereby decreasing the amount of cool air need to cool it?

We have a 1960's split level and spacepak had been installed since. Not sure when since been in house only 5 years. What maintenance is required on blower unit or coils? Other parts I don't know of require maintaining? I do clean the compressor outside and change the air filter in return, but anything else? THANKS

Some friends of ours offered to lend us one of their portable units (which I had never heard of before). It's the small 8500 btu unit and I roll it around to what ever room I'm working in. It plugs into a 110 outlet and doesn't require a drain. It does need to vent the hot air out somewhere, but doesn't necessarily require a window for the vent. We'll be getting one or two of these things for ourselves. I'd like to have one out in the shop!