My parents have Goodman GMP075-3 up flow furnace. Furnace sets in a hall closet in the middle of the house. Under it is where they originally cut the drywall for the return when the house was built.Filter sets in the inside the base of the unit. They want to replace the 1954 return grill. Size now is 31 3/4 by 9 3/4. I would like to know what the right size of grill I would need for proper return. 31 3/4 wide is as far as I could go but I can go bigger then 9 3/4 if I need to. Thanks, jmb

[Edited by jmb on 07-09-2005 at 10:51 AM]