Moving A/C supply vents - cost savings?
I have a 13-year-old home that I built new, but did not realize during construction that my builder's HVAC contractor took the cheap route and installed my A/C supply vents in (generally) the middle of each room rather than near a window on an exterior wall. And I was too stupid at that time to realize what had been done.
A couple of local AC guys were stunned to see how my vents were laid out - no vents near the greatest heat transfer. One guy said it was clearly a matter of a contractor going cheap and quick rather than right. A look in the attic clearly shows one main, large conduit with clearly a minimum number of branches for the room vents. Two of our bedrooms have their supply vents about 36"-48" from the return air, and I've noted that cold air is getting sucked right back up into the system the way it is.
What it boils down to is that while my A/C works and the house stays cool, its costing a small fortune presumably because my vents are really trying to cool essentially the majority of the space in the house rather than cooling the heat entering through the windows.
Bottom line - I need to move the vents to the walls with outside windows in nearly every room in the house. A local A/C contractor won't touch the job this summer, but said he'd probably be willing to tackle it for $1K later in the fall.
My question is this: Is there any way to predict or model just how much I stand to save by moving these vents so I can gauge the payback time? I (now, years after the fact) know this installation is terribly inefficient.
I was planning to add extra insulation, but I can't really do that until the vents are moved because guys crawling in the attic would squash the new insulation.
Any thoughts or feedback would be appreciated.