How to Choose Filters for Rooftop Package Units

Rooftop package units can be simple in concept, but filter selection is rarely straightforward. Access height, weather exposure, limited clearance and servicing access all affect what will work best in practice, especially when the unit sits in a harsh commercial or industrial setting.

For mechanical contractors and facility managers, the right choice is not just about particle capture. It is also about how the filter fits, how it seals, how it is changed, and how it performs between inspections when the unit is exposed to sun, wind, rain and rooftop dust.

Start with the unit, not the filter label

Before choosing a filter, confirm the filter arrangement inside the rooftop package unit. The frame size, filter depth, holding method and available access all matter.

A filter that looks suitable on paper may be a poor fit if the unit has tight access panels, shallow tracks or limited space for removal. In rooftop units, this can quickly turn a routine task into a frustrating one.

Check the following before ordering:

• •Exact filter dimensions, including depth and sealing edge
• •Whether the unit uses one panel, multiple panels or a filter bank
• •How filters are retained, such as clips, tracks or access doors
• •Whether there is room to remove the filter without bending or tearing it
• •Whether there is enough working space around the rooftop unit for safe servicing

If you need help confirming dimensions, how to measure an air filter is a useful starting point.

Match the filter to the site conditions

Rooftop package units often sit in dirtier and harsher environments than indoor plant. Windborne dust, leaf litter, nearby traffic, roof debris and construction activity can all influence how quickly filters load up.

The right filter depends on what the system is trying to do and what the site is throwing at it.

Consider these practical questions:

• •Is the site close to roads, car parks, loading docks or dusty external areas?
• •Is the unit exposed to heavy roof dust, pollen, salt air or industrial debris?
• •Does the building have a known issue with water ingress around the unit?
• •Is the system serving general ventilation or a space with tighter filtration needs?

For ventilation systems, AS 1668.2:2024 is often part of the discussion, but site requirements should always be confirmed with the mechanical services engineer or building owner. Rating choice should suit the application, not just a general assumption that a higher grade is always better.

Choose a filter rating that fits the application

Filter ratings are useful, but they should be read carefully. MERV, EN 779 and ISO 16890 do not convert directly, so avoid assuming that one rating automatically matches another.

In Australian projects, you may still encounter G3/G4 and F5-F9 references. These are EN 779 classes, which are now superseded by ISO 16890, but they are still widely used in Australia. What matters is selecting a filter that suits the airflow, dust load and service expectations of the unit.

A few practical points help narrow the choice:

• •Lower resistance can be helpful where the unit has limited fan margin, but the filter still needs to suit the site dust load
• •Finer filtration may be needed where the indoor environment or downstream equipment calls for it
• •A staged approach may work better than trying to do everything with one filter
• •If the system uses a final filter stage, make sure the prefilter is doing enough of the work upstream

If the system requires a high-efficiency final stage, note that HEPA grades are specific and should be selected carefully. H13 is at least 99.95% efficient, and H14 is at least 99.995% efficient at the most penetrating particle size under EN 1822.

Think about access and servicing from the outset

A rooftop package unit is only as manageable as its service access. If the filter is awkward to reach or hard to remove, servicing becomes slower and more likely to be delayed.

That matters because rooftop filters are often inspected and replaced as part of broader maintenance visits. If the design makes access difficult, maintenance teams may be tempted to postpone the job or use whatever is on hand rather than the correct replacement.

Good servicing design usually means:

• •Filters can be removed without tools where possible, or with simple, consistent tools where not
• •The access panel opens fully and safely
• •The filter does not snag on corners or sharp edges
• •Replacement filters are standardised across multiple units where practical
• •Pressure drop can be checked where gauges are fitted, so condition can be monitored rather than guessed

If your team handles ongoing maintenance, filter servicing and commercial filter servicing can help keep the process organised.

Weather exposure changes how filters behave

Rooftop units live with the weather every day. Heat, UV exposure, wind-driven dust and rain can all affect surrounding components and the ease of servicing.

While the filter itself is inside the unit, the rooftop location still affects performance in practical ways. Gaskets can dry out, housings can distort, debris can collect around the access area and wet weather can make rooftop work slower and less safe.

That means the filter solution should be robust enough for the site, not just technically correct in a clean test environment.

Useful considerations include:

• •Choosing a filter and frame arrangement that seals reliably even after repeated maintenance
• •Avoiding filters that are easily damaged during installation or removal
• •Making sure the housing is kept clean so debris does not compromise the seal
• •Considering whether the site needs a prefilter to handle heavier rooftop dust before it reaches the final stage

Some filters are designed to be washable - check the product instructions before deciding whether that option is suitable for your site and maintenance team.

Plan for replacement practicality, not just initial fit

The best rooftop filter is one your team can actually maintain consistently. That means thinking about supply, storage, handling and replacement compatibility from the start.

Questions worth asking include:

• •Can the filter be sourced in a standard size, or does it need a custom make?
• •Will the same filter suit multiple rooftop units on the site?
• •Is the frame rigid enough for repeated handling?
• •Is there a clear way to identify the correct replacement once the old filter is removed?
• •Does the site keep spares on hand for urgent maintenance needs?

Where a standard size does not suit the unit or the access arrangement, a custom solution can save a lot of trouble later. custom air filters are often the cleanest answer when a rooftop unit has unusual dimensions, depth limitations or special sealing requirements.

Choose a supplier who understands the real-world job

Rooftop package units need filters that fit the equipment and the maintenance routine, not just the catalogue description. A good supplier should be able to help with sizing, media selection and practical replacement options.

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, established 2009. We work with mechanical contractors and facility managers who need filters that suit the realities of rooftop access, weather exposure and ongoing servicing.

If you are reviewing a rooftop unit, ask for help with standard or custom options, and compare the filter choice against the access conditions and site dust load. You can also browse our products or see the industries we supply for more context on the types of applications we support.

Need help selecting the right rooftop filter?

If you want a practical recommendation for a rooftop package unit, Total Air Filtration can supply or make the right filters for the job. Call 07 3800 3448 or request a quote and we can help you match the filter to the unit, access and servicing needs.