About two years ago, I bought a custom home as a builder's foreclosure. Great buy, but obviously some unknowns in it. My first great surprise was that it was plumbed to run two 40 gallon gas water heaters and two furnaces from a 3/4" gas line. That's now been replaced with the 1.5" line.

The home is a three story town house with a total square footage of 3860. I'm currently running a 4 ton and a 5 ton unit. Unfortunately, and I'm almost certain that it has undersized ducting to most of the rooms. For instance, the master bedroom has one 6" duct for a room that is 14' x 17'. About half of the rooms have similar duct sizing issues. Of course, if this were a one story and all was coming in from the attic, reducting would be a reasonable approach. But it's three stories. Of the contractors I've spoken with, one suggested reducting, which was going to be a lot of expense and misery for a long time during construction. The other suggested a larger blower motor, I assume to force more air through the system along with some type of a valve on certain ducts to turn them down where they didn't need it.

My fear is that with a larger blower motor that it would also create noise of air rushing through the ducts, especially if one were closed a bit with the valve. Is this correct? Any other options?

The other odd thing is that the 4 ton until supplies the first two levels of the house, which are mostly open to one another. There is a second story loft area that opens to the first floor. The 5 ton unit is supply just the top level, which is basically 1/3 of the square footage and more isolated than the first two floors (only a stair case leading up to that floor). Given the under plummed gas line (which I still can't understand how it passed inspection), I'm fearful that the two units are actually reversed - the 5 ton should be for the first two floors and the 4 ton for the third floor. Is this a valid assumption? Is the fix to this as simple as rotating the equipment?

Thanks in advance!