Managing Wet-Season Odours in Shopping Centre HVAC Systems

Wet-season weather can make shopping centre odours harder to ignore. When outdoor air is damp and indoor surfaces stay cooler for longer, moisture can linger in plant rooms, ceiling spaces, return-air paths and lightly used tenancies, allowing stale or musty smells to travel further through the HVAC system.

For facility managers, the challenge is not just the smell itself, but how air movement spreads it across food courts, retail corridors, amenities and shared back-of-house areas. Filtration will not remove every source of odour, but the right filter selection and maintenance approach can help capture airborne dust, lint and other material that can contribute to that heavy, damp-air feeling.

Why wet weather makes odours more noticeable

During the wetter months, shopping centres often deal with a mix of moisture, low airflow pockets and more frequent door opening from customers and deliveries. That combination can make ordinary background odours seem stronger.

Common reasons include:

• •Damp carpets, mats and floor coverings holding moisture longer than usual
• •Condensation on ductwork, grilles or around poorly insulated services
• •Musty return air moving from service areas, amenities or plant rooms
• •Dust and organic debris trapped in coils, filters and ducts, then disturbed by airflow changes
• •Tenancies with intermittent use, where air stagnates and odours build up before trading resumes

When filters are heavily loaded, airflow can become uneven. That can allow stale pockets of air to sit in parts of the centre and make odours feel more noticeable even when the source is not obvious.

How filtration affects odour movement

Filters do not remove odours directly in the way a carbon medium can, but they still play an important role in how clean and stable the air system feels during wet weather.

A suitable filter setup can help by:

• •Capturing airborne dust that may carry musty smells
• •Reducing the amount of lint and fine debris recirculating through the system
• •Helping keep coils and internal components cleaner for longer
• •Supporting steadier airflow when the filter is matched correctly to the system

For shopping centres, the goal is usually to balance air cleanliness, pressure drop and maintenance access. A filter that is too open may allow more particulate loading deeper into the system. A filter that is too restrictive may reduce airflow or create nuisance pressure drop if it is not selected for the unit and duty.

If you are reviewing options, it can help to compare our products with the specific needs of each air handling unit rather than using one filter type across the whole site.

Filter media and odour-prone environments

In odour-sensitive areas, the filter media and frame design both matter. For example, some systems benefit from a staged approach, with a pre-filter taking the larger load before a finer final filter.

That can be useful where the building has:

• •High pedestrian traffic
• •Entrances exposed to wet weather and windblown debris
• •Food preparation areas nearby
• •Tenancies that create grease, paper dust or packaging debris
• •Limited access for frequent maintenance

Where odour control is a recurring issue, some sites also use activated carbon stages or other specialist media alongside particle filters. The right solution depends on the source of the odour and the design of the system.

Practical checks for facility teams

Before changing filter grades or adding specialist media, it is worth looking at the wider system. Wet-season odours often come from a combination of air quality, drainage, housekeeping and maintenance issues.

Useful checks include:

• •Inspecting condensate drains and trays for standing water or blockages
• •Checking for damp insulation, water ingress or roof leaks near air intakes
• •Reviewing toilet exhaust balance and any short-circuiting of air paths
• •Looking for signs of mould, dust build-up or stagnant air in returns and plenums
• •Checking whether external air intakes are positioned where rain splash, vehicle exhaust or litter can be drawn in
• •Confirming that access doors and panel seals are intact

If you are unsure about the physical size or fit of a replacement filter, our guide on how to measure an air filter can help before you order.

When filters should be inspected

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.

In a shopping centre, that is especially important during wet weather because dirty or damp filters can shift quickly from serviceable to underperforming if the system is carrying more debris than usual.

Some filters are designed to be washable - check the product instructions before cleaning or reusing them. If a filter is not intended to be washed, cleaning it can damage the media or reduce performance.

Choosing filtration for shopping centres

The right filter choice depends on how the centre is zoned and how the HVAC system is set up. Different areas can need different approaches.

A practical review might consider:

• •Main air handling units serving public corridors
• •Food courts and adjacent tenancy return air paths
• •Amenities and service corridors
• •Basement car park interfaces, where odours can move through doors and penetrations
• •Plant rooms and other low-traffic spaces where moisture can remain trapped

In many centres, finer final filters are selected where air cleanliness needs are higher, while pre-filters are used to protect the main filter and manage debris load. If your site uses EN 779 terminology such as G3, G4 or F5-F9, remember those classes are still widely used in Australia, but they do not convert directly to MERV or ISO 16890 ratings.

Where high-efficiency filtration is specified, it is important to be precise. HEPA H13 filters are at least 99.95% efficient at the most penetrating particle size under EN 1822, and H14 filters are at least 99.995%. Whether a HEPA stage is suitable should be assessed against the system design and the actual site requirement.

AS 1668.2:2024 is relevant to ventilation design, but site requirements should be confirmed with the mechanical services engineer or building owner before making changes to filtration or airflow arrangements.

Keeping odours from spreading through the system

Filtering better is only part of the answer. To limit musty air movement, the HVAC system also needs a sensible maintenance and housekeeping approach.

A good wet-season checklist includes:

• •Checking that outdoor air intakes are clear and not affected by leaf litter, rubbish or splash-back
• •Making sure wet mats, carpet runners and cleaning equipment are not left near return-air paths
• •Reviewing whether any areas need more targeted exhaust or air balance adjustments
• •Replacing damaged or collapsed filters promptly
• •Keeping spare filters on hand for known high-load periods
• •Recording pressure drop readings so changes can be compared over time

If the issue is recurring in a particular zone, it may be worth reviewing whether a standard replacement filter is still the best fit, or whether commercial filter servicing could help with a more regular inspection and replacement plan across the site.

Talk to Total Air Filtration

At Total Air Filtration, we are a family-owned air filter manufacturer and supplier based in Hillcrest, Brisbane QLD, and we work with facility teams to match filters to real site conditions, including wet-season odour concerns.

If you need replacement filters, a custom size, or help reviewing a shopping centre system, call 07 3800 3448 or request a quote. You can also contact us to discuss the options for your site.