Pocket filter guide: measure frame size and bag depth, compare ISO 16890 classes, pressure drop and replacement compatibility.
Pocket (bag) filters are used in many air-handling units, especially larger ventilation systems. Their flexible pockets provide a relatively large filter-media area within a defined face size. If you need to replace one, confirm the frame size, pocket depth, number of pockets, filtration class and pressure drop before ordering. These details matter more than a generic product description.
Quick checklist: identify the equipment and original filter; measure frame width and height, pocket depth and frame thickness; count the pockets; check the exact filtration rating and operating airflow; consult the equipment manufacturer’s specification.
A traditional pocket filter consists of several bags of filter medium attached to a supporting frame. The bags increase the media area relative to the front opening. The actual efficiency, resistance and dust-holding performance depend on the filter’s construction, media and operating conditions, not simply on the number or length of the bags.
Frames may be made from metal, plastic or other suitable materials. Some rigid multi-pocket or compact designs use a different construction from traditional flexible bags, so their specifications should not be treated as interchangeable without verification. Pocket filters are common in air-handling units; many residential heat-recovery ventilation (MVHR/HRV) units instead use flat or pleated panel filters.
G4, M5 and F7 are older EN 779 designations still found in equipment documentation. ISO 16890 expresses particulate filtration performance using classes such as ISO Coarse, ISO ePM10, ISO ePM2.5 and ISO ePM1. There is no universally exact conversion between the old and new systems. Check the tested rating of the specific replacement element.
A finer filter does not automatically have a higher initial pressure drop in every design; media area and construction can change the result. However, a change in filtration class must be assessed against the fan’s available pressure and the equipment’s required airflow.
Matching only the nominal front dimensions is not enough: the frame must seal correctly, fit the mounting rails and leave sufficient clearance for the pockets during operation. A difference in dimensions or design may lead to air bypass or mechanical interference.
Start with the equipment manufacturer’s manual or the specification for the original filter. Verify the required filtration class, the relevant airflow and the permissible pressure resistance. Where those data are available, compare the initial pressure drop of the candidate filter at the same airflow. Consider also its dust-loading behaviour and recommended final pressure drop.
Outdoor particulate pollution and the intended application influence filtration requirements. But an apparently higher-efficiency substitute is not automatically appropriate for the fan, mounting frame or installation. Where measurements or specifications are uncertain, ask the filter supplier to confirm the proposal before ordering.
The replacement interval is determined by the manufacturer’s instructions, operating conditions and, where fitted, differential-pressure measurement or a maintenance indicator. Airflow changes, contamination and a rising pressure drop can all prompt inspection. Do not assume all pocket filters have one fixed service life.
A heavily loaded filter can restrict airflow or increase the fan effort needed to maintain it. Replace damaged or saturated disposable elements, and do not wash them unless the manufacturer’s instructions specifically allow cleaning.
Custom manufacturing may be considered if the required frame size, depth or mounting arrangement is unusual. A supplier should be given the outer frame dimensions, frame thickness, pocket count and depth, filtration rating, airflow, equipment model and estimated quantity. A drawing and photographs are useful for avoiding misunderstandings.
A product advertised as compatible should still be checked against the original specifications; compatibility does not imply that the part is made by the ventilation-unit manufacturer.
This article is provided as technical information about pocket filters. Pocket filters are not currently listed in the ZenAero residential replacement-filter catalogue. Our current catalogue focuses on compatible filters for specific residential ventilation units, including flat and pleated designs. If your system uses one of those formats, you can browse the ZenAero filter catalogue and select a compatible replacement by make and model.
For a pocket-filter enquiry, first collect the technical details above. Availability or a custom solution would need to be confirmed individually; this article is not an offer of a stocked pocket filter.
No. Pocket count alone does not determine filtration efficiency or airflow resistance. You need the complete technical specification at the intended airflow.
Only after checking the actual efficiency, dimensions and pressure drop, and whether the equipment manufacturer permits that replacement. EN 779 and ISO 16890 are not directly interchangeable.
Frame width and height, frame thickness, pocket depth and count, plus mounting details and the filtration rating.
Brand names and trademarks mentioned in this article belong to their respective owners and are used to identify equipment or replacement-part compatibility.
