For the return duct from the return intake to the plenum, the contractor used the attic joists with no liner, etc. He simply blocked each end with sheet metal plates. The house is very old and the attic is not conditioned/finished so I doubt the attic floor provides a very tight seal for this return vent. Is that method acceptable for my geographic area (Virginia)?
Next, even if this is acceptable, is there sufficient space for air flow on the return side given the following: Although the air return vent is about 18x24 inches (3 square feet), the joist bay openings (two joist bays were used) are somewhat less. The joists are about 12 inches on center and are 2x8s thus you only have an opening of about 1 square foot (12 inches times 2, less nominal width of center joist and outside joist, times 8 inch height yields about 152 square inches, about 1 square foot (144 squire inches)). The A/C size is a 3-ton unit.
Thanks in advance.
[This message has been edited by JamesPatrick (edited September 04, 2002).]