A. A grille is a louvered covering for an opening through which air passes; a return grille is any opening through which air is removed from a conditioned space; a register is equipped with a damper or control valve, and directs air in a non spreading pattern; a diffuser is an outlet discharging supply air in a spreading fan-shaped or 360° pattern.

Q. How do I determine the correct size?

A. The opening, or hole, is the critical measurement in determining the correct size. For floor and sidewall applications, measure both the vertical and horizontal length of the opening. If the vertical measurement of the opening is 4 inches and the horizontal measurement of the opening is 12 inches, the correct size to cover your floor opening would be 4" x 12". When ordering sidewall products specify the horizontal dimension first.