Choosing Filters for Open-Plan Office Zones with Mixed Occupancy

Open-plan offices can look uniform from the outside, but the air conditions inside are often anything but. Desks near entries, breakout spaces, meeting points and areas close to outdoor air paths can all place different demands on the ventilation system as occupancy changes through the day. The right filter setup needs to suit those shifting conditions, not just the floor plan on paper.

Start with how the space is actually used

Before choosing a filter, map the office by use rather than by room name. A quiet focus zone with steady occupancy behaves differently from a collaborative area that fills up for meetings, lunches or training sessions.

In mixed-occupancy spaces, think about:

• •Where people gather at peak times
• •Which zones stay lightly occupied for much of the day
• •Which areas have doors opening frequently
• •Which parts of the office are closest to outside air intake paths, loading areas or nearby traffic
• •Whether the system serves the whole floor evenly, or whether some branches carry more dust load than others

This matters because filters are selected to work with the actual air conditions the system sees. If one zone regularly draws in more outdoor particles or sees heavier use, that section may need different attention during servicing or a different filtration approach within the same system.

Match the filter to the load, not just the label

Open-plan offices usually rely on a staged filtration approach, with a pre-filter or coarse filter upstream and a finer filter downstream. That arrangement helps capture larger particles first, which can support better performance from the finer stage.

For office systems, filter selection is often influenced by:

• •The outdoor air quality around the building
• •Whether the air handling unit is bringing in a high proportion of outdoor air
• •The amount of dust, lint or general debris carried through the system
• •The sensitivity of the work area and equipment served by the system
• •The pressure capability of the fan and the condition of the existing ductwork

If the system is under strain from changing occupancy or a dustier intake location, a better-sequenced filter set can be more practical than simply choosing a denser final filter. The goal is to capture particles without creating unnecessary resistance that the system cannot handle.

Where higher-efficiency filtration is being considered, it should be checked against the unit’s operating limits and the wider mechanical design. If you are working to AS 1668.2:2024 or another project requirement, confirm the site arrangement with the mechanical services engineer or building owner before changing the filter specification.

Pay attention to the zones closest to outdoor air paths

In many office buildings, some parts of the open plan sit closer to outside air intakes, doors, car parks or service entries. Those areas can see a different mix of dust and outdoor particles compared with the centre of the floor plate.

That does not always mean the whole building needs the same filter upgrade. Instead, it can mean you should focus on the intake side of the system and the sections that experience the heaviest incoming load.

Useful questions include:

• •Is outside air being drawn in near a dusty driveway or landscaped area?
• •Do doors open often enough to bring in extra debris?
• •Are some zones receiving more fresh air than others because of system balancing?
• •Does the filter pressure rise faster in one air handling unit than another?

If a zone near the outdoor air path is carrying more dirt into the system, a better pre-filter can often help protect the finer filter stage. In some cases, duct placement, air balancing or louvre position may also need review. Filter changes alone do not solve a design issue, but they can be part of a practical response.

Consider pressure drop and service access

In a mixed-occupancy office, filters may load unevenly because people move around, rooms are used differently and some intakes sit in harsher locations. That means pressure drop monitoring becomes especially useful where gauges or differential pressure indicators are fitted.

Rather than relying on a fixed calendar, inspection frequency should depend on the system, site conditions and dust load. Follow the filter and equipment manufacturer instructions, and inspect more closely if:

• •The office has changed layout or occupancy pattern
• •Nearby construction has increased dust exposure
• •Doors, windows or loading access create more outside air ingress
• •The building has had complaints about airflow or dust build-up on grilles

Also consider how easy it is to access the filters. If the system is in a tight ceiling void, plant room or service corridor, the right filter choice is one that can be maintained safely and consistently. A filter that is too restrictive, awkward to handle or poorly sized for the frame can create avoidable maintenance problems.

For practical guidance on sizing and fit, see how to measure an air filter and compare the details with your current set-up.

Use the right filter type for the job

Office environments often use panel filters, pleated filters and bag filters in different stages, depending on the system and the level of filtration required. The best choice depends on the equipment, the intake location and the type of dust the system is handling.

A sensible approach is to think in layers:

• •A coarse or pre-filter to capture larger debris and protect downstream filters
• •A finer filter for smaller airborne particles in the supply air path
• •A product format that fits the frame properly and seals well in service

If you are comparing classifications, remember that MERV, EN 779 and ISO 16890 do not convert directly. G3/G4/F5-F9 are EN 779 classes that are still commonly referenced in Australia, even though ISO 16890 has superseded EN 779 for many applications. Keep the specification consistent with the system documentation rather than trying to force an exact cross-over.

Where a HEPA stage is being considered for a specific area or application, use the correct EN 1822 figures: H13 is at least 99.95% efficiency at MPPS, and H14 is at least 99.995% at MPPS. That level is not necessary for every office zone, so it should be selected for the job at hand, not as a default.

Some filters are designed to be washable, but that depends on the specific product. Check the product instructions before cleaning or reusing anything.

Keep servicing aligned with changing occupancy

Open-plan offices can change from calm to crowded in a matter of hours. That swing affects how quickly filters load, especially where outdoor air paths bring in extra dust or where foot traffic is heavy.

A good servicing plan should:

• •Track pressure drop where monitoring is installed
• •Note seasonal dust changes and nearby site activity
• •Include visual checks for damaged seals, bypass and frame distortion
• •Be adjusted when occupancy patterns or tenancy layouts change

If the office has multiple zones served by the same system, it can be useful to record which areas seem to drive the heaviest load. That helps with future filter selection and reduces guesswork when the time comes to order replacements.

If your office needs ongoing support, our filter servicing and commercial filter servicing pages explain the kind of maintenance support we provide.

Getting the specification right for your building

The best filter for a mixed-occupancy open-plan office is rarely chosen by size or rating alone. It is chosen by understanding how the space is used, where the outdoor air enters, how the system is configured and how much resistance the fan can handle over time.

If you are reviewing an existing office setup, it can help to document the zones, check the current filter frames and compare the physical dimensions before ordering replacements. If the system has unusual sizes or a special arrangement, custom air filters may be the most practical option.

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, established 2009. We can help supply or make the right filters for your office setup, including mixed-use and hard-to-fit systems. Call 07 3800 3448 or request a quote.