Grille Dimensions and Required Openings
| Grille Dimensions and Required Openings | (W x H) | ||
| Grille | Grille Exterior | Frame | Minimum Return |
| Size | Casing | Exterior | Air Duct Opening |
| 12 x 12 | 14 7/8 x 13 9/16 | 12 x 12 1/4 | 12 1/8 x 12 3/8 |
| 12 x 24 | 14 13/16 x 25 9/16 | 12 x 24 1/4 | 12 1/8 x 24 3/8 |
| 12 x 36 | 14 13/16 x 37 9/16 | 12 x 36 1/4 | 12 1/8 x 36 3/8 |
| 14 x 14 | 16 13/16 x 15 9/16 | 14 x 14 1/4 | 14 1/8 x 14 3/8 |
| 14 x 20 | 16 13/16 x 21 9/16 | 14 x 20 1/4 | 14 1/8 x 20 3/8 |
| 14 x 25 | 16 13/16 x 26 9/16 | 14 x 25 1/4 | 14 1/8 x 25 3/8 |
| 14 x 30 | 16 13/16 x 31 9/16 | 14 x 30 1/4 | 14 1/8 x 30 3/8 |
| 16 x 16 | 18 13/16 x 17 9/16 | 16 x 16 1/4 | 16 1/8 x 16 3/8 |
| 16 x 20 | 18 13/16 x 21 9/16 | 16 x 20 1/4 | 16 1/8 x 20 3/8 |
| 16 x 25 | 18 13/16 x 26 9/16 | 16 x 25 1/4 | 16 1/8 x 25 3/8 |
| 18 x 18 | 20 13/16 x 19 9/16 | 18 x 18 1/4 | 18 1/8 x 18 3/8 |
| 20 x 20 | 22 13/16 x 21 9/16 | 20 x 20 1/4 | 20 1/8 x 20 3/8 |
| 20 x 25 | 22 13/16 x 26 9/16 | 20 x 25 1/4 | 20 1/8 x 25 3/8 |
| 20 x 30 | 22 13/16 x 31 9/16 | 20 x 30 1/4 | 20 1/8 x 30 3/8 |
| 24 x 12 | 26 13/16 x 13 9/16 | 24 x 12 1/4 | 24 1/8 x 12 3/8 |
| 24 x 24 | 26 13/16 x 25 9/16 | 24 x 24 1/4 | 24 1/8 x 24 3/8 |
| 25 x 20 | 27 13/16 x 21 9/16 | 25 x 20 1/4 | 25 1/8 x 20 3/8 |
| 30 x 20 | 32 13/16 x 25 9/16 | 30 x 20 1/4 | 30 1/8 x 20 3/8 |
