if they have split..I've never tried to repair them, not much cost to replace. to repair the duct would have to be clean and dry and then use a mastic tape, but it won't stick if surfaces are not clean and dry. usually gray duct splits due to uv rays. wrapping them with another vapor barrier can cause condensation problems. best of luck

Basements which are mostly underground have a small heat load. In the summer the basement can actually become too cool if you leave the vents open. When I installed my new system I didn't get a separate zone for the finished part of the basement. I didn't think it was needed but now I know better. I would be concerned creating a zone for the 1500 sq ft basement with a single stage furnace. I am willing to bet the first floor system is over sized which further aggravates the problem. I suppose a contractor who is very good a zoning could do it correctly. But then again someone who understands the physics behind good zoning design would probably recommend upgrading to a variable speed 2-stage furnace.

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.

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