How AS 1668.2:2024 Affects Filter Specification in New Builds

AS 1668.2:2024 brings the ventilation standard back into focus for anyone designing or delivering new commercial and multi-residential HVAC systems. While the standard is not a filter catalogue, it can affect how filters are selected, documented and coordinated across drawings, schedules and equipment selections.

For mechanical contractors and building designers, the practical question is simple: what needs to be checked so the filter specification matches the system, the space and the project requirements? The answer starts with the drawings and schedules, then moves through access, pressure drop, filter class and maintenance planning.

Start with the design intent, not just the filter size

A filter schedule should do more than list a nominal size. Under a project governed by AS 1668.2:2024, the filter specification needs to suit the intended use of the space, the ventilation design and any site-specific requirements confirmed with the mechanical services engineer or building owner.

When reviewing the drawings, check that the documentation clearly shows:

• •the air handling unit or terminal equipment the filter belongs to
• •the filter stage or stages in the system
• •the required filter dimensions and depth
• •the direction of airflow
• •the service access arrangement
• •the pressure drop basis used for fan selection

If any of these items are unclear, the filter schedule can become disconnected from the actual equipment order. That is where installation delays, incorrect substitutions and avoidable site variations often begin.

Confirm the filter class and standard reference used on the project

One of the first things to check is which rating system the design team has used. In Australian projects, you may still see EN 779 class references such as G3, G4 or F5 to F9 on older documentation, even though ISO 16890 is now widely used. These systems do not convert directly, so the filter schedule should state the actual class or performance basis being specified rather than relying on assumed equivalents.

For higher-efficiency applications, HEPA filters may be specified where required by the project brief or equipment design. If HEPA is used, it should be identified correctly on the schedule, including the relevant EN 1822 class. H13 is at least 99.95% efficiency at the most penetrating particle size, and H14 is at least 99.995% efficiency at the most penetrating particle size.

It is also worth checking whether the design has allowed for a pre-filter and final filter arrangement. In many systems, that is the best way to keep the schedule practical and the plantroom easier to maintain, but the final arrangement should always match the equipment supplier’s guidance and the engineer’s design intent.

Check the drawings for the details that affect installation

Filter specification problems often come down to details that are easy to miss in a drawing package. A design may name the right filter class but still leave gaps around how it is actually installed.

Look for the following items in the drawing set and equipment schedule:

• •exact filter face dimensions and frame depth
• •whether the frame is rigid, disposable or reusable
• •the sealing method required in the frame or housing
• •the access side for removal and replacement
• •any restrictions caused by ductwork, pipework or nearby services
• •whether the filter bank needs a retaining arrangement or special holding frame

For multi-residential projects, access is especially important. If a filter can only be reached by moving other equipment or entering an awkward ceiling space, servicing becomes difficult and future maintenance may not follow the original design intent. If the access detail is not clear in the shop drawings, it is worth raising early.

Make pressure drop part of the specification conversation

Filter selection is not only about dust capture. It also affects fan duty, system resistance and how the plant behaves as the filter loads with dust.

When checking the schedule, confirm:

• •the initial pressure drop used for selection
• •the final or changeout pressure drop basis, if specified by the engineer or equipment manufacturer
• •whether gauges, differential pressure switches or other indicators are fitted
• •whether the design allows enough space for the filter to load without causing access or performance issues

This matters because a filter that is too restrictive for the application can create unnecessary operating issues, while a filter that is underspecified for the environment may need very close monitoring. The right balance depends on the system type, the dust load and the design conditions.

Inspection frequency should be based on the system, site conditions and dust loading, not on a fixed calendar rule. Follow the filter and equipment manufacturer instructions, and monitor pressure drop where gauges are fitted.

Match the filter to the environment and maintenance plan

Not every new build needs the same approach. A retail tenancy, apartment tower, office fitout or mixed-use development may each have different contamination sources, occupancy patterns and maintenance access constraints.

Design teams should check whether the schedule reflects the actual site conditions, including:

• •construction dust during commissioning and fitout
• •outdoor air intake location and exposure
• •internal dust sources from tenancy use or common areas
• •rooftop or basement plantroom conditions
• •whether the system needs a washable product or a replaceable filter element

Some filters are designed to be washable - check the product instructions before specifying or cleaning them. Where washability is mentioned, it should be supported by the product data, because not every filter media or frame style is suitable for washing.

For larger or more complex systems, it is also sensible to plan how filters will be serviced after handover. If the building has limited access, unusual dimensions or a non-standard frame, the maintenance team should know this before practical completion. If needed, filter servicing and commercial filter servicing arrangements can be discussed alongside the specification.

What to check before the order is placed

Before signing off the filter schedule, review the details that often trigger rework at procurement or installation stage:

• •Does the filter code match the actual equipment dimensions?
• •Has the correct class or performance basis been named?
• •Is there enough room for replacement access?
• •Has the pressure drop been coordinated with the fan selection?
• •Are pre-filters and final filters identified separately if both are required?
• •Has the engineer confirmed any project-specific interpretation of AS 1668.2:2024?
• •Is the maintenance team likely to be able to service the filter without dismantling nearby services?

If the answer to any of these is unclear, it is better to resolve it before the filters are manufactured or ordered. For unusual sizes or layouts, custom air filters may be the cleanest way to keep the specification aligned with the equipment.

Work with a supplier that can support the drawing set and the jobsite

AS 1668.2:2024 makes it more important for the filter specification to be clear, consistent and practical. That means checking the drawings, confirming the schedule and making sure the filter selection suits both the system and the maintenance plan.

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, established 2009. We can help supply the right filters for new commercial and multi-residential HVAC projects, including standard and custom sizes. To discuss a project or request support with a specification, call 07 3800 3448 or request a quote.

You can also view our products or contact us if you need help checking a drawing, measuring a filter or confirming a replacement detail.