YIDINGAIR FILTRATION
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YIDINGAIR FILTRATION
Technical Guides
2026-10-30
Why one air handling unit takes 592 × 592 mm filters and another takes 24 × 24 in, how nominal and actual sizes differ, and what to measure before ordering replacements.
Key points
Most air handling units are built around one of two systems. European and many Asian units follow EN 15805, which sets metric face sizes based on a 610 mm module, the metric equivalent of 24 inches. The filter face is made slightly smaller than the module so it slides into the frame: a full module becomes 592 × 592 mm.
Units built to US practice use nominal inch sizes such as 24 × 24 in or 12 × 24 in. The nominal size is a name, not a measurement: the real filter is a little smaller so that it fits the opening.
| Face size W × H (mm) | Share of a full module | Typical nominal airflow, pocket filter (m³/h) |
|---|---|---|
| 592 × 592 | Full | 3400 |
| 490 × 592 | 5/6 width | 2800 |
| 287 × 592 | Half width | 1700 |
| 287 × 287 | Quarter | 800 |
| 592 × 892 | Full width, 1½ height | 5000 |
Airflow figures are typical published nominal values for pocket filters; panel and compact filters can be rated differently. 3400 m³/h through 592 × 592 mm is a face velocity of about 2.7 m/s.
For inch sizes, always check the actual dimensions. Our own catalogue lists the actual size in millimetres next to each nominal size.
| Nominal size (in) | Typical actual size (in) | Actual size in our catalogue (mm) |
|---|---|---|
| 24 × 24 | 23⅜ × 23⅜ | 595 × 595 |
| 12 × 24 | 11⅜ × 23⅜ | 289 × 595 |
| 20 × 24 | 19⅜ × 23⅜ | 492 × 595 |
| 20 × 20 | 19⅜ × 19⅜ | 492 × 492 |
A 595 mm filter can jam in a frame made for 592 mm, and a 592 mm filter in a 24-inch frame leaves a gap around the edge. Air takes the easiest path, so even a small gap lets dust bypass the media, and the efficiency printed on the filter is lost. Gaskets and clamping clips close small differences, but they cannot fix a filter that is the wrong size.
They are close but not the same. A 24 × 24 in filter is about 594–595 mm in reality, which may be too tight for a 592 mm frame. Measure the frame opening before ordering.
It standardises the face dimensions of air filters for general ventilation, so filters from different makers fit the same frames and housings.
Only if there is space in the unit behind the frame. A deeper filter lowers pressure drop, but the pockets must not touch the coil or the unit wall.
Yes. We build filters to the dimensions you give us, so older or non-standard units can be supplied too.
