Acorn Cast Iron Floor and Wall Grilles: Inside and Outside Sizes, Screw Holes and Registers with Louvers

The old vent cover in your floor or wall is cracked or missing, and you want a cast iron one in its place. Most Acorn grille pages print two sizes, and the size in the item name is only one of them. Before you order, it helps to know which number is which, what the -D at the end of a model means and where a register differs from a grille.

Cast iron with a matte black finish

For this family Acorn answers the material question plainly. The Grilles and Registers list on acornmfg.com says the grilles are made from heavy cast iron, and Acorn describes its registers as having a traditional matte black finish on heavy cast iron. It adds that all of its grilles have a traditional matte black finish.

According to Acorn, the grilles can be used on wood floors, tile and wall-to-wall carpeting, and they come with or without holes to accommodate floor or wall openings.

ID and OD: which size is in the name

Most grille pages give two sizes, length by width in inches, marked ID (inside) and OD (outside). On those pages the ID matches the size in the item name, with one exception covered below. The GR6BG, for example, is sold as a 10 x 4 grille, with an ID of 10 x 4 and an OD of 12 x 5-1/2.

Here are the eleven grille sizes on Acorn's list, with the OD printed on each item page:

Do not work out an OD from a neighboring size. Acorn gives the 10 x 6 GRABG an outside width of 7-1/2 inches and the 12 x 6 GRBBG an outside width of 8. Take the figure from the row of the exact grille.

One page does not add up. The GR8BG is named 14 x 4 and its OD is 16 x 5-1/2, but the ID on its page reads 14 x 2-1/4, the size of the narrow GR4BG. If you need that grille, ask us before you order.

Acorn does not explain how to measure an opening or an old grille.

With or without screw holes: the -D numbers

On Acorn's list, a number ending in -D is the version with screw holes. GR4BG is the 14 x 2-1/4 grille, and GR4BG-D is the same size titled Grille with Screw Holes. Its page prints the same ID and OD as the GR4BG.

Ten of the eleven grille sizes are listed both ways. The 8 x 4 GR5BG appears only without holes. Acorn's pages do not tie either version to floors or to walls.

Grille or register: the louver

A register, as the GRBBG page puts it, includes the grille and a louver. Acorn says the same of its registers: the GL3BG comes with a grille and louver, and the GL4BG-D with a pre-drilled grille and louver. Acorn lists registers in five sizes, and each of them is also listed with screw holes:

Several grille pages say the grille is also available as a register, among them the 14 x 6 GRCBG and the narrow GR2BG and GR4BG. None of those sizes has a GL number on the list. Go by the table: a size that is not in it has no register on Acorn's list.

Several grille pages also mention louver assemblies, which Acorn calls air flow control, in five sizes. On the register pages, the GL1BG gives an ID of 10 x 4 and an OD of 12 x 5-1/2, the same as the GR6BG grille, and the GL4BG-D an ID of 12 x 6 and an OD of 14 x 8, the same as the GRBBG. The GL3BG page prints 10 x 6 for both the ID and the OD, so ask us about its outside size before you order it.

What the pages leave out

Acorn's grille and register pages give no airflow figures, no load ratings and no installation instructions. Questions about heating and air flow for a room belong with your HVAC contractor.

The grilles and registers we carry are listed with the rest of the Acorn range on our Acorn page.

Not sure which of the two sizes your numbers match, or have a size that is not in the tables? Our customer support team is available Monday - Friday, 8 AM - 4 PM Central Time, at 1-888-800-7789 or [email protected].