Australia has one of the world’s highest rates of asthma — approximately 2.8 million Australians, or 1 in 9, have the condition. Melbourne’s allergy and asthma burden is further elevated by the city’s unique climate: the combination of high grass pollen loads in spring, mould-promoting cool-wet winters, and high dust mite survivability year-round creates a significant allergen environment. For Melbourne households with a ducted heating and cooling system, that system is the primary mechanism distributing every indoor allergen throughout the home.
This guide covers the specific allergens that accumulate in Melbourne ductwork, the mechanism by which they affect allergy and asthma sufferers, and the evidence-based approach to reducing allergen exposure through duct cleaning and maintenance.
Allergens That Accumulate in Melbourne Ductwork
Melbourne’s four primary indoor allergen sources are all represented in duct contamination:
House dust mite allergens
House dust mites are the leading cause of year-round allergic rhinitis and a major asthma trigger in Melbourne. They thrive in soft furnishings, bedding, and carpets — and the dust they produce (primarily faecal particles containing the allergens Der p1 and Der p2) is distributed throughout the home by ducted systems. Melbourne’s moderate climate allows dust mites to survive year-round at lower levels even in winter, meaning ducted heating systems distribute mite allergen continuously through the heating season.
Pet dander
Cat allergen (Fel d1) is one of the most potent and persistent indoor allergens — it remains airborne for hours after disturbance and sticks to surfaces throughout the home. Dog allergen (Can f1) is similarly persistent. In Melbourne homes with cats or dogs, a contaminated duct system ensures dander reaches every room, including bedrooms where occupants spend 7 to 8 hours breathing accumulated allergens overnight. See our guide on duct cleaning for Melbourne pet owners for cleaning frequency recommendations.
Mould spores
Melbourne’s cool, damp winters create ideal mould growth conditions inside ducted systems that experience temperature differentials between the conditioned air and the roof space ambient. The most common allergenic mould species in Melbourne ductwork are Cladosporium and Alternaria — both established triggers for asthma and allergic rhinitis. Mould spore concentrations inside a contaminated Melbourne duct system can exceed outdoor levels during peak mould season. See our guide on mould in Melbourne air ducts.
Cockroach allergens
Cockroach allergen (Bla g2) is a significant sensitiser in inner Melbourne’s older housing stock — Victorian terraces, Edwardian bungalows, and inter-war era apartments. Cockroach droppings and shed body parts accumulate in ductwork and are a potent asthma trigger. This allergen is less discussed than dust mite or pet dander but is clinically significant for sensitised individuals.
How Ducted Systems Amplify Allergen Exposure
The mechanism by which a contaminated duct system increases allergen exposure is important to understand:
Continuous allergen redistribution
Without a ducted system, allergens settle from the air relatively quickly and concentration drops over time in a still room. With a ducted system running, settled allergens are continuously re-entrained into the airflow and redistributed throughout the home. The system creates a constant allergen cycling effect — every supply register is a source of allergen exposure, not just areas where pets live or where dust settles.
Bedroom exposure during sleep
Melbourne homes typically run ducted heating overnight in winter. Bedrooms with supply registers receive 7 to 8 hours of continuous allergen exposure during the period when occupants are most vulnerable — face close to bedding, breathing at elevated depth during sleep, immune system in overnight recovery mode. For asthma sufferers, nocturnal allergen exposure from ducted systems is a recognised driver of overnight symptom worsening.
Concentrated reservoir effect
The duct system acts as a concentrated repository for allergens that have been collected from across the home over years. When cleaning is deferred, this reservoir grows. Each time the system runs, it delivers a dose of accumulated allergens to every room in the home simultaneously — effectively the opposite of a clean room environment.
Reducing Allergen Exposure in Melbourne Allergy Households
A structured approach to allergen management in a Melbourne home with a ducted system:
Professional duct cleaning every 2 to 3 years
The primary intervention. Professional cleaning removes the accumulated allergen reservoir from duct surfaces. Post-clean, the system distributes significantly lower allergen loads with each cycle. The effect is cumulative over the weeks following the clean as residual surface allergens further diminish.
Higher MERV filter (8 to 11)
Upgrading from a standard MERV 4 to 6 filter to a MERV 8 to 11 filter captures finer particles including the sub-10 micron particles that carry most allergen. Confirm your system can accommodate the slightly higher static pressure of a higher MERV filter before upgrading — some older Melbourne ducted systems are not designed for high MERV filtration. Change at 3-month intervals in allergy households. See our air duct filter guide.
Encasement of bedding and soft furnishings
Allergen-impermeable mattress and pillow encasements reduce the primary source of dust mite allergen in bedrooms — reducing the amount that enters the ducted system’s return air path. This is a complementary measure to duct cleaning, not a replacement.
Humidity control
Dust mites require above 50% relative humidity to thrive. Keeping bedroom humidity below 50% significantly reduces mite allergen production. Melbourne’s dry winter heating season naturally reduces humidity, but poorly ventilated bathrooms and kitchens in older homes can maintain localised high-humidity zones that sustain mite populations year-round.