Duct Size	A	B	C
6 inch	20"	3"	6" x 12"
8 inch	20"	3"	8" x 12"
10 inch	20"	3"	10" x 12"
12 inch	20"	3"	12" x 12"
14 inch	20"	3"	14" x 12"
16 inch	20"	3"	16" x 12"
18 inch	20"	3"	18" x 12"
20 inch	20"	3"	20" x 12"
24 inch	20"	3"	24" x 12"

 

The size of the access door is a function of the nominal duct size.  As a standard, we cut the doors to a 12" width, making the minimum overall length of the access door fitting 20".  This can be customized to your particular application.