Undermount Floor Vent Size Guide
Undermount floor vent sizes
Eight sizes: 2x12, 3x10, 4x10, 4x12, 4x14, 6x10, 6x12 and 6x14, the widest range we make.
Undermount sizing has two numbers that matter, and mixing them up is the one mistake that ruins an install. The duct opening is the hole in the floor, and it decides which size you order. The tray cut-out is what you cut in the subfloor so the tray can drop in and sit flush. They are different numbers. Cut to the tray cut-out.
Measure your DUCT OPENING. Match it to the range below.Your opening must fit within the range shown for the size you pick. Install the undermount base before laying your flooring. The flooring insert cut sizes below are for the piece that fits inside the tray, not the subfloor opening.
2 × 12
3 × 10
4 × 10
4 × 12
4 × 14
6 × 10
6 × 12
6 × 14
| Size | Duct openingMust fit within this range | Flooring insert cut sizeFlooring piece inside the tray |
|---|---|---|
| 2 × 12 | 2–2½″ × 11¾–12¼″ | 1.02″ × 10.67″26 × 271 mm |
| 3 × 10 | 2¾–3¼″ × 9¾–10¼″ | 1.77″ × 8.70″45 × 221 mm |
| 4 × 10 | 3¾–4¼″ × 9¾–10¼″ | 2.76″ × 8.70″70 × 221 mm |
| 4 × 12 | 3¾–4¼″ × 11¾–12¼″ | 2.76″ × 10.67″70 × 271 mm |
| 4 × 14 | 3¾–4¼″ × 13¾–14¼″ | 2.76″ × 12.64″70 × 321 mm |
| 6 × 10 | 5¾–6¼″ × 9¾–10¼″ | 4.72″ × 8.70″120 × 221 mm |
| 6 × 12 | 5¾–6¼″ × 11¾–12¼″ | 4.72″ × 10.67″120 × 271 mm |
| 6 × 14 | 5¾–6¼″ × 13¾–14¼″ | 4.72″ × 12.64″120 × 321 mm |
How to measure
Replacing a vent?Pull the old one out and measure the bare duct opening. Match it to the duct opening range.
Installing undermount?Measure the actual vent base and duct opening before preparing the subfloor. Use the flooring insert cut size only for the flooring piece that sits inside the tray.
Works with flooring up to 20 mm (~13/16 in) thick.
Flooring insert cut size is the size of the flooring piece placed inside the vent tray. It is not the subfloor or duct opening size.
Free area and airflow by size
Free area is the open cross-section air actually passes through, not the outside of the cover, and not the nominal size on the label. It is the number that decides how much air a vent moves. We publish it for every size we sell.
| Size | Duct opening | Duct opening (mm) | Free area | Open | Airflow | Price |
|---|---|---|---|---|---|---|
| 2x12 | 2.17″ × 11.89″ | 55 × 301.9 mm | 13.4 sq in | 50% | ≈ 46 CFM | from $54.99 CAD 2x12 / 1 |
| 3x10 | 2.91″ × 9.92″ | 73.9 × 251.9 mm | 12.2 sq in | 41% | ≈ 42 CFM | from $54.99 CAD 3x10 / 1 |
| 4x10 | 3.89″ × 9.92″ | 98.9 × 251.9 mm | 13.3 sq in | 33% | ≈ 46 CFM | from $54.99 CAD 4x10 / 1 |
| 4x12 | 3.89″ × 11.89″ | 98.9 × 301.9 mm | 15.3 sq in | 32% | ≈ 53 CFM | from $59.99 CAD 4x12 / 1 |
| 4x14 | 3.89″ × 13.85″ | 98.9 × 351.9 mm | 17.3 sq in | 31% | ≈ 60 CFM | from $59.99 CAD 4x14 / 1 |
| 6x10 | 5.86″ × 9.92″ | 148.9 × 251.9 mm | 15.4 sq in | 26% | ≈ 54 CFM | from $59.99 CAD 6x10 / 1 |
| 6x12 | 5.86″ × 11.89″ | 148.9 × 301.9 mm | 17.4 sq in | 24% | ≈ 61 CFM | from $64.99 CAD 6x12 / 1 |
| 6x14 | 5.86″ × 13.85″ | 148.9 × 351.9 mm | 19.4 sq in | 23% | ≈ 68 CFM | from $69.99 CAD 6x14 / 1 |
Per-size detail:2x12 ·3x10 ·4x10 ·4x12 ·4x14 ·6x10 ·6x12 ·6x14 ·
Figures are calculated from factory drawings at 500 fpm face velocity with the damper fully open. See exactly how we calculate them, including what these numbers do and do not account for.
Frequently asked questions
Which number do I cut to?
The tray cut-out. The duct opening tells you
which size to buy; the tray cut-out tells you what to cut.
What if my flooring is thicker than 20 mm?
The tray is designed for
flooring up to 20 mm (~13/16"). Above that the grille will sit proud.
Get in touch before ordering.
Can I fit an undermount without lifting the floor?
No, the tray goes under
the flooring, so it needs the floor open. If the floor is staying down, use a
drop-in floor vent instead.
Do undermount vents have a damper?
Yes, adjustable, so you can balance
airflow room by room.