Guy who lives around the corner from me asked me for some advise. I didn't know the answer, but told him I'd try and find out. In his house he has 2 7&3/4 x 31&1/2 R/A grills and 1 7&3/4 x 13&1/2 R/A air grill. Is it hard to find filter grills for this application? It's understood that he's going to have open up the walls to accomadate a slighty larger grill then he has. Can you get a R/A fil. grill say like 10 x 15 or 16, or something like 10 or 12 x 32 or 34?