20" X 20" Steel Access Panel Removable Door For Concealed Wall / Ceiling Application With Slotted Lock - [Outer Dimensions: 21" Width X 21" Height] Compatible with Duct 8" Actual Filter Size – 29 4 X 12 Is CRFG2028 Width_14in

Actual Filter Size – 29 3/4"w x 9 3/4" x 1"

The ring base allows installation without removing the thermostat

+ Product Details Perfect Fit & Easy Sizing - Designed for a 22" x 26" OR 26" x 22" duct opening (measured at the opening)

+ Product Details Size - 4"w X 26"h is the size for the duct opening measurement only

these grilles offer both functionality and aesthetic appeal

20" X 20" Steel Access Panel Removable Door For Concealed Wall Ceiling Application With Slotted Lock [Outer Dimensions: 21" Width X 21" Height] Compatible with Duct 8" Actual Filter Size – 29 4 X 12 Is CRFG2028 Width_14in Actual Filter Size – 29 3 4"w x 9 3 4" x 1" The ring base allows installation without removing the thermostat