Thanks all! It sounds like, on this forum, no one is worried about a ductless unit being able to supply these three bedrooms via ducts (that is what one salesperson was trying to tell me--he'd not ever use these with a duct run longer than 6 feet, and certainly not 3 duct runs...) In fact he said, the ductless system is "rated at only .2"w.c maximum. Typical duct systems are designed at a .5"w.c. static pressure, the low static units are best suited to having the air outlet directly against a sidewall and the air inlet directly below the unit,..." This is where it definitely goes above my understanding, but the salesperson trying to sell the ducted ductless system says they just size up the ducts so there isn't as much resistance on the interior head. I just wish there was a lot more information available (in English) on these systems and how they have been used well.

tommy, you talk about a LOT of things! so your ducts are ductboard with 2 flex ducts? ductboard is rigid fiberglass insulation board with foil surface facing into the attic, flex is flexible duct with foil insulation jacket. 1" ductboard is R-4.2 (just fyi) the first thing I would look at is how is this duct system sealed..duct tape..foil tape..mastic seal? duct tape fails..doesnt take long in extreme attic temps, foil tapes (unless mastic tapes) also fail quickly. tapes don't adhere to dirty or wet surfaces, although they may look to be intact when the system is running you will be able to feel air escaping from these areas. sealing with a paint on mastic or cleaning and drying surfaces and sealing with a mastic tape is the better, longer lasting option. you can buy mastics at hvac supply stores. areas of leakage on duct board would be areas where duct board sections connect, and each supply duct. flex would be where it attaches to ductboard plenum. these areas should be sealed with a paint on mastic sealant. the other area of duct leakage is the supply box. if you feel around the supply boxes in the attic, they should sit evenly without gaps on the attic floor. lots of times the side attached to the ceiling joist makes a snug fit, but the opposite side (not attached to anything) will raise up when supply grills are installed. I use Hardcast mastic tape to seal these areas from inside the house by removing supply grills. heat is an issue here also, today it is 92 degrees outside and RH is 87%. it isn't a bad thing that your unit runs alot when temps are so high. shortcycling, unit running 10 minutes on and 10 minutes off adds to cost of utilities, does not remove humidity and wears out equipment sooner. You may want to think about upgrading to a higher SEER heat pump, 10 SEER is not very efficient and is no longer mfg'd because of inefficiency and cost of operation. Federal tax credits can help to offset costs. in adding more insulation to the attic...did you use layers of unfaced insulation?? the paper backing (vapor barrier) causes condensation between vapor barriers..this can cause more harm than good. under the house the insulation should be in contact with the underside of the flooring, or condensation occurs between the gap between the underside of the floor and the insulation. I'm not sure what you mean by double bubble wood siding for your walls... foil bubble foil wraps are not good insulators, and in our hot humid climate vapor barrers are to the exterior of the walls. cold climates have vapor barriers to the interior, but here promotes mold growth. If you are insulating the exterior of your walls, a foam sheathing board with all seams taped is the best option. to upgrade the insulation from R-13 in the walls to R-15 is a minimal cost and would be of benefit to you. if you are not working from the exterior to the interior ..well..enough for now..that can be discussed later. Like the attic ventilation...not enough info! for your windows in your home, adding a piece of glass to the screens really isn't your best improvement. check HD and Lowe's for Gila brand window tint. these will reduce heat gain, whereas two panes of glass that are not insulated glass units will trap heat between the panes of glass. I understand perfectly about being 57 and this being the last big undertaking..I'm 48 and just getting too stiff for some of this stuff! That you are happy with a $300 plus utility cost just blows me away! My last utility bill was $70.00 my little house is about 950 sq ft full sun, just plantings in the yard to block west sun from the windows. when I first bought this house my utility bill was $275 - $300 a month. Knowing where and how to correctly address specific issues in the house makes a lot of difference! You can get help specific to your home that will make all this time, effort and money spent worthwhile. visit http://www.natresnet.org/directory/raters.aspx to locate an energy rater in your state.

Disclaimer: I'm a homeowner not a plumber. How about something like this: Quiet Wrap⢠Pipe Soundproofing Wrap (see link below) I came upon it when searching for noise abatement of a HVAC duct which started last winter when a new more powerful solenoid was installed for our whole house humidifier. It causes the Aprilaire to suck quick and tightly to the furnace return, sending off pressure waves etc on the vent ducts. I haven't tried the noise reducer yet, but sure enough, with the heat and humidifier back this weak on the specific HVAC duct noise is audible and I believe traceable. None of the HVAC men seem to want to replace the offending copper solenoid, nor check part number on the Aprilaire humidifier. I think it's just too much of a load so I'll probably call them. Read up on flammability and check with local code department for your booster pump though if you consider using this tape. I'm not familiar with booster pumps (hot water delivery related)? Good luck. Here is a link that might be useful: Sound proofing wrap

I think in this case the room was an addition 50 years ago with no HVAC. Then 4 years ago the house was renovated and they decided the simplest solution would be to run this vent across the roof (it looks like there is no other solution internally, based on how these rooms connect. No way to get from the original attic into that room with the flat roof.) Despite being insulated from the inside, the duct does in fact blow hot air for the first few seconds and then clears out to colder air, which is obviously not efficient. So I guess the big question is, whether that duct is even built for outdoors. and can ever be waterproofed.