Homeowner symptom guide · Melbourne
Mould in Air Conditioning: Causes, Health Risks & What to Do
Melbourne's humid winters and warm summers create ideal conditions for mould growth inside air conditioning systems — particularly in ducted heating and cooling units that sit unused for months before being needed. When these systems restart, they can spread mould spores throughout the entire home, affecting air quality for all occupants. This guide explains the causes and the correct response.
Take the free home risk check →Common Causes
- • Moisture in ductwork: condensation in ducted systems — particularly in poorly insulated ducts running through cool roof spaces — creates persistent moisture that supports mould growth inside the duct lining.
- • Dirty evaporator coils: the wet evaporator coil in a split system or ducted system accumulates organic dust that, combined with moisture, becomes a mould growth medium.
- • Blocked condensate drain: a split system's condensate drain removes moisture during cooling cycles. When blocked, water accumulates in the drain pan and feeds mould growth that eventually appears on the unit's interior and air louvers.
- • Long periods of inactivity: systems left unused between seasons retain moisture in filters and coils without the drying-out effect of regular operation, making mould establishment faster.
When to Be Concerned
- Musty or earthy smell when the system runs
- Visible black or grey spots on or near air supply vents
- Household members experiencing increased respiratory symptoms, particularly when the system runs
- Dust and debris being expelled from vents when the system first starts
What to Do
- 1 Do not continue running a system you suspect has mould — this spreads spores throughout the home. Turn it off and arrange professional cleaning.
- 2 Clean or replace filters immediately — filters are typically accessible without tools and can be washed with warm soapy water and left to dry fully.
- 3 For split systems: arrange professional coil cleaning and internal inspection ($150–$300) — the evaporator coil requires careful chemical cleaning that goes beyond what filters cover.
- 4 For ducted systems with suspected duct mould: HVAC duct cleaning ($400–$800 for an average home) is required — this is not a DIY task.
Frequently Asked Questions
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Is mould in a ducted system dangerous to health?
Yes — particularly for people with asthma, allergies, or compromised immune systems. Mould spores spread by a ducted system can accumulate in bedrooms and living areas at levels that trigger respiratory symptoms. Children and elderly household members are most vulnerable.
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Can I clean mould from my split system myself?
Filter cleaning is a safe and recommended DIY task. Cleaning the evaporator coil and internal components requires specific chemical agents and knowledge of the refrigeration system — attempting this without training risks damaging the coil and can void the warranty.
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