4x12 Metal Floor Vents: Free Area, Airflow and Duct Fit
A 4x12 floor vent has a free area of 17.5 square inches and a calculated airflow of 61 CFM, and it drops into a duct opening of 98 x 300 mm.
- Duct opening
- 3.86″ × 11.81″
- Metric
- 98 × 300 mm
- Best free area
- 17.5 sq in
- Comes in
- Drop-In · Upgraded 2-in-1 · Undermount
4x12 keeps the 4-inch duct width and adds two inches of length, and at 17.5 square inches it is the highest free area of any Drop-In we make.
Free area and airflow at this size
| Product | Free area | Open | Airflow | Price | |
|---|---|---|---|---|---|
| Drop-In Floor Vent [Metal] | 17.5 sq in | 37% | ≈ 61 CFM | from $31.49 | View 4x12 |
| Upgraded 2-in-1 Drop In Vent with Insert | 17.5 sq in | 37% | ≈ 61 CFM | from $39.99 | View 4x12 |
| Undermount Flush Floor Vent [Metal] | 15.3 sq in | 32% | ≈ 53 CFM | from $59.99 | View 4x12 |
Free area is the open cross-section air actually passes through, not the outside of the cover. How we calculate it.
Measuring for this size
The extra length is in the duct rather than in cover overhang, so the Drop-In wants a 98.0 mm by 300.0 mm opening and the Undermount 98.9 mm by 301.9 mm. A 4x12 will not drop into a 4x10 hole without opening the joist bay another two inches.
Can I open a 4x10 hole up to a 4x12 for more airflow?
Yes, and it is worth about 18 percent on the Drop-In: 17.5 square inches against 14.8, or 61 calculated CFM against 51. The Drop-In needs a 98.0 mm by 300.0 mm opening and the Undermount 98.9 mm by 301.9 mm. The branch duct behind the vent has not changed, so the real gain depends on the system.
Does the 2-in-1 4x12 flow the same as the plain Drop-In 4x12?
Yes. Both are built on the same tray and duct geometry, so both publish 17.5 square inches of free area and 61 calculated CFM. The 2-in-1 adds a matte black insert for appearance. The drawings we hold are for the vent without the insert fitted, so email support@khansupply.co if you need a figure for that.
How do I measure for a replacement vent?
Measure the duct opening, not the old cover. Pull the existing vent out, measure the hole itself across the width and the length in millimetres, and match that to the duct dimension listed on this page. Vent sizes are named for the duct, so a vent called 4x10 has a face larger than 4 by 10 inches. Measuring the faceplate is the single most common reason a size arrives wrong.
What happens if I order the wrong size?
Email support@khansupply.co with your order number and the millimetre measurements of your opening, and we will work out which size actually fits and sort out the exchange. Every Khan Supply vent also carries a 2-year warranty against defects, which is separate from a fit exchange.
What does shipping cost?
Nothing. Shipping is free on every order across North America, on a single vent and on a 5-pack alike. You will get tracking by email once the order is on its way. If a vent arrives damaged, photograph the box and the part and email support@khansupply.co, Monday to Friday 9 to 5 ET, and we reply within one business day.
Every Khan Supply vent is all metal, not plastic, and ships free across North America with a 2-year warranty. If a size is wrong, email support@khansupply.co and we sort out the exchange. Mon-Fri 9-5 ET, one business day reply.
Not sure of your size? · All sizes and free-area figures · Every size we make