4x10 Metal Floor Vents: Free Area, Airflow and Duct Fit
A 4x10 floor vent has a free area of 14.8 square inches and a calculated airflow of 51 CFM, and it drops into a duct opening of 97 x 250 mm.
- Duct opening
- 3.82″ × 9.84″
- Metric
- 97 × 250 mm
- Best free area
- 14.8 sq in
- Comes in
- Drop-In · Upgraded 2-in-1 · Undermount
4x10 is the most common floor register size in North American homes: 14.8 square inches of free area and 51 calculated CFM on the Drop-In, 13.3 and 46 on the Undermount.
Free area and airflow at this size
| Product | Free area | Open | Airflow | Price | |
|---|---|---|---|---|---|
| Drop-In Floor Vent [Metal] | 14.8 sq in | 37% | ≈ 51 CFM | from $29.69 | View 4x10 |
| Upgraded 2-in-1 Drop In Vent with Insert | 14.8 sq in | 37% | ≈ 51 CFM | from $37.99 | View 4x10 |
| Undermount Flush Floor Vent [Metal] | 13.3 sq in | 33% | ≈ 46 CFM | from $54.99 | View 4x10 |
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
Measure the hole in the floor rather than the old faceplate. The Drop-In is built for a 97.0 mm by 250.0 mm duct opening and the Undermount for 98.9 mm by 251.9 mm, and every faceplate is larger than the duct it covers.
Why is the 4x10 only 37 percent open when the 3x10 is 44 percent?
Because free area is the ring around the inner tray, and widening a vent from 3 to 4 inches adds face area faster than it adds perimeter. The 4x10 has more free area than the 3x10 in absolute terms, 14.8 square inches against 13.2, but it spreads that over a larger face, so the percentage drops.
Can I put an area rug or furniture over a 4x10 floor vent?
You can, but you will lose most of the airflow. The 4x10 Drop-In relies on a 14.5 to 17.0 mm slot around the tray, and anything resting on the face closes it. If the room needs that outlet, a 4x12 elsewhere on the same branch is a better answer than covering the vent.
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.
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