yes. by foaming the roofline you have moved the air barrier & the thermal barrier from the attic floor to the roofline. this makes all the kneewalls, non air tight recessed lights, between floor penetrations, oversized cuts at supply boxes, stove vents etc no longer suck from hot attic. as this air will not be drawn into first & second story...it reduces the amount of tons required. people building tightly, and foam insulating rooflines are achieving 700 to 1,000 sq ft per ton with the better building practices. not that I'm a fan of sq ft per tons sizing. last summer a friend of mine built a 3800 sq ft house with a 4 ton zoned system one system...4 tstats. the wife homeschools 7 kids..in the summer they are in and out of the pool all day. I teased them that they should have put in revolving doors they open & close them so much. the most comfortable house...acording to them... ever. affordable to heat & cool. great comfort lowered costs of equipment as opposed to the 2 three ton systems spec'd by every hvac company in their area. they got an independent load calc, duct design & sizing, shopped the calcs to local hvac companies. took them months to find the right company. but it is great. their highest utility bill in our mild winter this year was $100. with the highest utility costs in the state and a not so great water heater choice. in two years they will move the existing water heater to their camp & put heat pump water heater in attic. if they had access to gas..they'd put a tankless on the outside of the house..its mild enough winters here for that. shop carefully lex mom. this is important. be aware that their job is to sell equipment and not have call backs..thus the oversizing. the next thing they will want to do, is expensive. variable speed/ staged units set on low tonnage. (5 ton set on 3 ton capacity) so that on those 7 100 degree days..you'll have capacity & not call them. however..the cost of equipment really gets up there. you should talk to an energy rater in your area to find out who will properly size & install. if they can give you some company names of folks that truly understand what you are trying so hard to achieve..it may save you a lot of time. check this site for someone close to you for a consultation. www.resnet.us this hvac oversizing issue is probably 75% of why people hire independent energy raters. one day...maybe...foam companies & hvac will work together..or so I keep hoping! best of luck.

1. Is there a measurement (decibel reading) that tells me how loud the unit is (inside blowing noise and outside the house). - Yes, there is a decibal rating but I believe that it is for the outside unit only. The inside blowing noise (at the vents) is more of a function of duct design and blower speed. A 14 SEER unit and above will have a variable speed fan which should be more quiet than a fixed speed fan. 2. Where's the break point SEER for energy efficiency (say a 5 year payback)? I know that 13 is the new standard, but is it worth going up to 17 SEER? - Ah, the mother of all questions. Depends on electric rates, climate, and system usage. You say that the climate is temperate most of the year so the system usage will be fairly minimal compared to Texas or Florida. How are the electric rates in CA? I would think that payback from a 14 SEER to 17 SEER would be 10 years or more in your situation but I do not know the rates. 3. What is a typical warranty? 1 year, 10 yr? - Some systems are 5 year warranty, some are 10 year. Major parts only, labor is another issue. 4. Does the suitcase models require less maintance than the full size units? Are their any benefits to suitcase models besides the size? - Not sure what you mean by "suitcase models"? Good luck to you.

You need to sit down with the contractor and go thru all of that in detail with them. There is just too much detail and unknowns in this for me to give advise here. It never hurts to get more opinions. The dampers will work if installed correctly and will help the upstairs a lot. I like that contractors proposal.

Sizing can be less of an issue when you have multiple units. Because each unit is controlled independently, provided of course the unit itself is not over sized for the area in which it serves resulting in excessive short cycling. In your case 3 ton plus 2 ton isn't necessarily equal to 5 tons of cooling... unless you drive those thermostats really low. By having two systems with total capacity of 5 tons (which, most of the time this would be oversized for a 1700 - 1800 sq ft structure) has a few advantages. 1. You have the ability to use one system only during low heat days or set the opposing unit higher. The unit set higher only runs if load conditions warrant.... meaning if it's not hot, the thermostat controlling the unit does not call... the unit can not run without a call... 2. Utility bills can be much less... because you rarely use both systems at the same time. You run the bedroom system when you sleep, the other when you're awake. If you have a home office in one the bedrooms you may need to rethink things a bit. 3. Extra capacity for when it's hot out. When it's hot you have the capacity to cool the home. (even while entertaining guests --- additional people add heat) Remember heat waves come, heat waves go... a so call 'properly sized' AC system is essentially properly sized roughly 10% of the time... especially if that system is a single speed AC system. Alot of people I come across like to sleep cool. So for that reason I doubt I would change the configuration of the space. Once you realize what you have, the choices you make are mostly budget type concerns. Essentially a set up like this runs like a 2 stage system. This kind of subject is above the pay grade of many... choose your contractor wisely. I service the Katy, Texas area.