Measure the opening in your floor, wall or ceiling. The width and length of your opening should match the duct opening sizes.
1. Note if the register or grille you are replacing is for a wall, ceiling or floor.
2. Remove screws holding the vent in place. If the vent is held in place by its own weight or tension, pull the vent forward and out of the opening.
3. Measure the size of the air duct opening. Do not measure the old register or vent. Write down the measurements as Width and Length because this is how register and grille packaging is labeled.
4. Make note of the size of the existing hole, you will want to ensure the register or grille you choose will cover the opening. Look for units with wide borders to compensate for large openings.