Bag Filters, Pocket Filters and ISO 16890: How Ratings Influence Specification

When you are specifying filters for a larger air handling system, the filter type is only part of the decision. Bag filters and pocket filters can look similar at a glance, but their construction, media area and rating class all influence how they behave in service, how much space they need, and how well they fit the duty of the plant.

For mechanical contractors, facility managers and industrial buyers, the practical question is not just “what rating do I need?” It is also “what filter construction suits the airflow, casing depth, access and maintenance approach of this system?”

Why construction matters as much as rating

Bag and pocket filters are both used in commercial and industrial air handling units where a large filter area is needed within a compact frame. The folds, pockets or bags increase the effective media area, which helps the filter hold dust and manage resistance to airflow.

That construction detail matters because two filters with a similar rating can behave differently in the field. A deeper pocket filter may suit a system with more available depth and a need for longer dust holding capacity. A shallower bag filter may suit a tighter plant space or a retrofit where access is constrained.

When selecting a filter, consider:

• •Available filter depth in the frame or housing
• •Airflow volume and face velocity
• •Access for removal and replacement
• •Dust loading from the site environment
• •Whether the system uses pre-filtration upstream
• •Pressure drop limits set by the equipment design

A filter that fits physically but is too restrictive for the system can create unnecessary resistance. A filter that is too open for the application may not provide the level of particle capture the site needs.

How ISO 16890 changes the way filters are specified

ISO 16890 is the current rating system used to describe particulate air filters by their efficiency against particle size ranges. In practical terms, it helps buyers and designers compare filters based on how they perform on airborne particles that are relevant to real systems, rather than relying on older class labels alone.

That said, ratings do not tell the whole story. Two filters with similar ISO 16890 designations can still differ in construction, media type and installed performance. This is why specification should always look at both the rating class and the physical design.

For example, a system may need a filter that balances capture performance with manageable resistance over time. In that case, the construction becomes just as important as the efficiency class printed on the product data.

If you are working from legacy drawings or existing plant records, you may still see older EN 779 class references such as G3, G4 or F5 to F9. These classes are still widely used in Australia, even though ISO 16890 has superseded EN 779. They do not convert directly, so avoid assuming one-to-one equivalence when you replace filters or update specifications.

Bag filters and pocket filters in larger AHUs

In larger air handling systems, bag and pocket filters are often used as the main medium-efficiency stage or as part of a staged filtration arrangement. The right choice depends on the air volume, the contaminants in the intake air, and how much room is available in the filter section.

Bag filters

Bag filters are often selected where the system needs a large media area in a relatively simple format. They are commonly used in commercial HVAC applications and can offer a practical balance between dust holding capacity and footprint.

Useful checks when specifying bag filters include:

• •Frame dimensions and sealing arrangement
• •Number of bags and bag depth
• •Media type and stiffness under airflow
• •Whether the filter is intended for front access or side access housings
• •Compatibility with the existing holding frame

Pocket filters

Pocket filters use multiple pockets of media to increase surface area. They are often chosen for air handling systems where the filter section can accommodate the pocket depth and where a stable, even airflow profile is important.

Pocket filter specification should take into account:

• •Pocket length and spacing
• •Support structure within the frame
• •Whether the pockets will have adequate clearance when loaded with dust
• •The risk of turbulence or crowding in compact filter banks
• •The required balance between capture efficiency and pressure drop

For both styles, the installation conditions matter. If the filter bank is poorly sealed or the frame is distorted, even a well-rated filter may not perform as intended.

Choosing the right rating for the application

ISO 16890 rating selection should follow the function of the system and the air quality expectations of the site. A general ventilation system, a manufacturing space and a data or process environment may all need different approaches.

Some practical specification questions are:

• •Is this a primary filter, a secondary filter or a final stage?
• •What contaminants are most relevant at this site?
• •Is the goal to protect equipment, improve indoor cleanliness or support process conditions?
• •Are there upstream filters already reducing the dust load?
• •What pressure drop range can the system tolerate?

Where older project documents still refer to EN 779 classes, use caution. G3/G4/F5-F9 classes may help describe historic performance expectations, but they should not be treated as a direct translation to ISO 16890.

If you are working on a building design or upgrade, the ventilation arrangement should also be considered against AS 1668.2:2024, with site requirements confirmed by the mechanical services engineer or building owner. The filter choice needs to suit the overall system design, not just the label on the carton.

Maintenance, access and inspection planning

The best filter specification is not only about initial performance. It also needs to make sense over the life of the system, including how often the filter bank can be inspected and how easily elements can be changed.

Inspection frequency depends on the system, site conditions and dust load. Follow the filter and equipment manufacturer instructions, and monitor pressure drop where gauges are fitted. That is often the most practical way to know when a filter bank is approaching its service limit.

A few points worth confirming before ordering:

• •How the filter is inserted and removed
• •Whether the frame is reusable
• •Whether there is enough access space for safe handling
• •Whether a pre-filter stage is in place to extend downstream filter life
• •Whether replacement sizes match the actual opening, not just the nominal size on drawings

Some filters are designed to be washable - check the product instructions. Do not assume washability unless the manufacturer states it clearly.

If you need help checking dimensions, our guide on how to measure an air filter is a good starting point before you place an order.

Matching the filter to the site environment

No two sites load filters in exactly the same way. A warehouse intake near traffic, a production area with fine airborne dust, and a commercial building with standard fresh air demand different filtration choices.

The most reliable specification process is to work backwards from the site conditions:

• •Identify the source of airborne particles
• •Confirm the airflow and housing size
• •Decide whether bag or pocket construction is better suited
• •Select the appropriate ISO 16890 class
• •Check access, sealing and replacement handling
• •Review whether upstream or downstream stages are needed

If the site has special requirements, custom sizing or non-standard frame details may be needed. In that case, custom air filters can be a practical option when standard products are not the right fit.

For buyers across different sectors, our industries we supply page can also help you think through the type of application before you specify a filter.

Specifying with confidence

Bag filters and pocket filters are both useful in larger air handling systems, but the right selection depends on more than the rating label. Construction, media area, frame fit, airflow conditions and maintenance access all affect how the filter performs in service.

At Total Air Filtration, a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, established 2009, we help customers choose or make the right filters for the job. If you need support with a replacement specification, a custom size or a project order, call 07 3800 3448 or request a quote. You can also contact us to discuss your application.