There are two types of return filter grilles namely fixed bar type grille and a stamped face grille. A high flow return grille is type of return grille that is much more aerodynamic than a stamped face return grille. The louvers positioned on a fixed bar return grille are further apart, and are designed much more aerodynamically than those of a stamped face grille. A high flow return grille has essentially more open area to let air flow through the actual grille.
