Plastic Grille Boxes

Plastic grille boxes — also called plenum boxes — are the missing link between round ducting and a square grille, louvre or diffuser. The box mounts behind the grille, and the round connection takes rigid or flexible duct, giving a clean, sealed transition inside the ceiling void or wall cavity. Made from high-quality, impact-resistant plastic, they are light to handle, easy to fit and suited to both residential and commercial installations. Without one, connecting a round duct to a square grille means fabricating an adaptor; with one, it is a straight push-fit job.

The range covers face sizes from 100mm x 100mm up to 550mm x 550mm, each offered with a choice of circular duct connections from 100mm up to 500mm — including the standard 125mm, 150mm, 200mm, 250mm, 315mm and 355mm duct sizes in between. That means you can match the box to your grille first, then pick the spigot to suit the duct run.

Pair a grille box with our eggcrate grilles, 4-way diffusers or square weather louvres. Order by 3pm for next-day delivery on stocked sizes.