Standard sizes cover most air handling units, but older plants and purpose-built housings often need an element that no catalogue lists. A custom size is a production decision, so it needs the same technical file a serial product would have.
Measure the housing opening, not only the old element
A filter that has been in service is compressed at the gasket and may have swollen or distorted media. Record the clear opening of the housing, the depth available to the clamping mechanism and the position of any rails or lugs. Keep the old element until the replacement is approved, and photograph its label before it is discarded.
State the dimension order and which dimension is critical
Write dimensions as width x height x depth in mm, and say which face you are looking at when you call one of them width. Then mark the dimension that cannot move. A frame can usually absorb a millimetre on height, while the depth that seats against a clamping bar often cannot. Tolerances belong on the drawing, not in an e-mail sentence.
Describe the frame, seal and flow direction as a set
Frame material, seal type, seal position and flow direction decide whether the element can be fitted at all. A gel seal needs a matching channel; a gasket needs a flat seating surface of a known width. Working directly with the manufacturer that produces the element shortens this stage, because frame and seal options are production choices rather than catalogue entries.
Agree the approval route before production starts
For a custom size, decide in advance what is approved and by whom: the drawing, a first article, or a sample installed on site. Record who signs the drawing, how revisions are numbered and what happens if the sample does not seat. A custom tool or fixture may make later changes expensive, so revisions are cheaper before the first production run.
Field example
Example: A housing opening measures 610 x 610 mm, but the old element measures 605 x 605 mm with a compressed gasket. The correct request states the opening, the gasket thickness in free condition and the clamping travel, rather than repeating the worn element's dimensions as the new specification.
Practical checklist
- Clear housing opening, available depth and clamping travel
- Dimension order in mm and the dimension that cannot move
- Frame material, seal type, seal position and flow direction
- Drawing revision, approval signature and sample route
Send Safe Air the dimensions, requested class, airflow per element and quantity. Identify missing information and confirm product and document scope during quotation review.
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Frequently Asked Questions
A label identifies a starting point. Confirm the housing opening, seal geometry and flow direction against a drawing or measurement before the size is released for production.
No. Where the interface is documented and the drawing is approved, a first article check can be enough. A sample is useful when the seating surface or clamping mechanism is uncertain.
