How to Match Filters to Mixed HVAC Systems in a Strata Building

Strata buildings rarely run on one simple HVAC setup. Apartments, corridors, basement car parks and shared amenities often use different equipment, different airflows and different filtration needs, so a single filter approach usually creates avoidable problems. The practical goal is to match the filter to the system and the space it serves, while keeping maintenance straightforward for the building team.

Start with the system, not the filter

Before choosing any replacement filter, identify exactly what each piece of plant is doing. In a mixed strata complex, one system may serve tenant apartments, another may handle common corridors, and a separate exhaust or supply arrangement may serve the car park or gym.

That matters because the filter must suit the fan, ductwork, housing and intended air quality outcome. A filter that works well in a common area air handling unit may create too much resistance in a smaller apartment system. On the other hand, a light pre-filter may not be enough for a corridor unit that sees higher dust loading from foot traffic and open doors.

A good starting point is to gather:

• •the make and model of each air handler, fan coil or exhaust unit
• •existing filter dimensions and frame type
• •filter class or rating currently specified
• •whether the system uses return air, outside air or both
• •whether there are pressure gauges or ports for checking pressure drop
• •any notes from the mechanical services engineer or building owner about site requirements

If dimensions are unclear, how to measure an air filter is a useful reference before ordering replacements.

Match filter performance to each area

Different parts of the building place different demands on the filter.

Apartments

Apartment systems are often limited by space, access and fan capacity. In many cases, the aim is to capture everyday dust without overloading the equipment.

When selecting a filter for apartment air conditioning or ventilation systems, consider:

• •the available filter slot depth and face area
• •whether the unit needs a panel filter, pleated filter or another format
• •how much resistance the system can handle without affecting airflow
• •whether the apartment receives outside air through the system or only recirculates indoor air

If the original equipment specified a particular G, MERV or ISO class, keep in mind that these ratings do not convert directly. The safest approach is to follow the equipment documentation or get guidance from the building’s mechanical services engineer.

Corridors and common areas

Corridors, lobbies and shared lounges often benefit from a more considered filtration setup because these spaces see more movement, more doors opening and more airborne dust being carried in. Depending on the system design, a finer final filter may be appropriate, but only if the fan and housing can support it.

For common area systems, it is worth checking:

• •whether the filter rack can accept a deeper or higher-capacity filter
• •whether there is room for staged filtration, such as a pre-filter followed by a finer final filter
• •whether the system operates continuously or only during set periods
• •whether nearby works, landscaping or road traffic are increasing dust load

If the building uses filters that fit under the older EN 779 wording, G3, G4 and F5-F9 are still widely used in Australia even though EN 779 has been superseded by ISO 16890. Don’t assume a direct replacement based on label alone; confirm the actual dimensions and intended performance.

Car parks

Basement car parks usually need a very different approach again. These systems may be handling dust, lint and other fine particles drawn in from vehicle movement and outside air. In some buildings, the filtration is tied to supply or exhaust fans that are critical to overall ventilation performance.

For car park systems:

• •confirm whether the unit is supply, exhaust or smoke control related
• •check that the filter type does not restrict airflow beyond what the fan can manage
• •inspect housings for corrosion, moisture and build-up around the frame
• •select filters that are robust enough for the site conditions and easy to replace safely

If a system is part of a broader ventilation arrangement, site requirements should be confirmed with the mechanical services engineer or building owner, particularly where AS 1668.2:2024 is relevant to the ventilation design.

Build a maintenance plan around pressure drop and site conditions

With mixed HVAC systems, the biggest mistake is treating all filters as if they load up at the same rate. They won’t.

Inspection frequency depends on the system, the site conditions and the dust load. A coastal building, a site near construction, or a complex with high vehicle movement will usually need closer attention than a low-dust site. Follow the filter and equipment manufacturer instructions, and monitor pressure drop where gauges are fitted.

Pressure drop is a practical indicator of when a filter is becoming restricted. If the reading is rising, the system may be working harder than intended, airflow can change, and the building team may start seeing complaints about uneven performance. Regular checks also help you spot issues such as:

• •filters fitted the wrong way around
• •damaged frames or seals
• •bypass air around the filter edge
• •water ingress or condensation damage
• •unusual dust build-up that points to another fault in the system

Some filters are designed to be washable - check the product instructions before attempting cleaning, and never assume a washable style based on appearance alone.

Make replacement simpler across multiple systems

A strata complex is easier to manage when the filters are standardised where possible, but only where the equipment allows it. The aim is not to force one product across every system; it is to reduce confusion, ordering mistakes and emergency callouts.

Useful ways to simplify the job include:

• •creating a site register of each unit, its filter size and its recommended filter type
• •labelling filter housings clearly so the right replacement goes in the right place
• •keeping a record of frame style, thickness and gasket requirements
• •storing one or two spare filters for critical plant, if the building manager approves it
• •confirming whether custom sizes are needed for older or modified equipment

If a filter housing is unusual or the size is non-standard, custom air filters can be a practical way to keep the system operating without forcing a poor fit.

For larger buildings, it also helps to separate routine replacement work from more involved plant servicing. Our filter servicing and commercial filter servicing pages are useful starting points for planning that work.

What to check before ordering

Before placing an order, make sure the replacement is based on the actual system rather than a rough guess. A few minutes spent checking the details can save a lot of site disruption later.

Confirm:

• •exact width, height and depth
• •whether the filter has a cardboard, metal or plastic frame
• •whether the unit needs an airside seal or gasket
• •whether the old filter had a higher or lower dust holding capacity than the proposed replacement
• •whether the system needs a coarse pre-filter, a medium filter or a finer final filter
• •whether there are access limits that affect the maximum usable depth

If the building has a mix of legacy and newer equipment, it is often worth reviewing the full inventory together rather than ordering area by area. That gives the strata manager and contractor a clearer picture of where standardisation is realistic and where bespoke sizing is unavoidable.

Practical support for strata sites

Mixed HVAC systems need a filter supplier who can work across apartments, corridors, car parks and shared spaces without forcing one-size-fits-all assumptions. Total Air Filtration is a family-owned air filter manufacturer and supplier based in Hillcrest, Brisbane QLD, and we can help you match the right filter to the right system.

If you need help identifying sizes, choosing a replacement type or organising a site-specific supply plan, call 07 3800 3448 or request a quote. You can also contact us or view our products to get started.