The WEB, WEB Plus and Absorber
adjustable filters trim to fit these sizes:

14x20 14x24 14x25
15x20 15x24 15x25
16x20 16x24 16x25
17x24 17x25 18x20
18x24 18x25 20x20
20x24 20x25

No trimming is necessary if your filter is 20" x 25".