Ducted gas heating is the dominant heating system in Melbourne — installed in the vast majority of homes built from the 1960s through to today. These systems share a duct network between every room in the home, meaning whatever accumulates in the ductwork — dust, allergens, mould spores — circulates to every room every time the heater runs. Regular professional cleaning of the duct network is the key maintenance step that preserves both system performance and indoor air quality through Melbourne’s long heating season.
Why Ducted Gas Heating Ducts Get Dirty in Melbourne
Melbourne’s extended heating season — typically April through October — means ducted gas heaters run for 6 to 7 months per year. During that time, the entire volume of home air is recirculated through the duct system repeatedly. Every airborne particle in the home has a chance to be captured by the return air path or to settle inside the duct network.
The accumulation process
Return air drawn through the filter captures most particles, but no residential filter captures everything — particularly fine particles below the filter’s MERV rating. Over a heating season, a thin layer of fine dust deposits on the inner surface of every duct run. Over 2 to 3 seasons without cleaning, this layer becomes a significant debris load — compacted enough to reduce the effective cross-section of the duct and provide an organic substrate for mould growth during the system’s inactive summer period.
Melbourne winter conditions and mould risk
Melbourne winters are cool and damp — conditions that favour mould growth. When the gas heater is turned off for summer, the duct network sits inactive in a roof space that has absorbed ambient humidity during winter. Any organic debris in the ducts — dust, pollen, pet dander — provides substrate for mould growth during this inactive period. The mould then circulates throughout the home when the heater starts up in autumn. This is why Melbourne gas heating systems that have not been cleaned for several years often produce a musty smell on first use each winter. See our guide on musty smell from vents in Melbourne.
What a Ducted Gas Heating Duct Clean Involves
Step 1: System off and setup
The gas heater is switched off and the thermostat disabled. The negative pressure extraction machine is connected to the duct system — typically via the return air grille or a supply register near the system unit. All other supply registers are sealed to direct the full extraction vacuum to the section being cleaned.
Step 2: Return air duct cleaning
The return air duct — from the return grille to the system unit — is cleaned first. This section often has the heaviest debris load because it receives all return air before filtration. A rotary brush is used to dislodge material from the duct walls, with the negative pressure machine simultaneously extracting the dislodged debris.
Step 3: Supply duct branches
Each supply register is removed. The flex duct branch serving that register is cleaned by negative pressure extraction and rotary brush from the register end back toward the trunk line. Registers are vacuum cleaned and reinstalled. This process is repeated for every register in the home — typically 8 to 14 for a standard Melbourne 3 to 4 bedroom home.
Step 4: Main trunk line
The main trunk line — the primary distribution duct running from the system unit through the roof space — is cleaned by a combination of compressed air agitation and negative pressure extraction. The trunk line handles the full system airflow and accumulates a proportionally higher debris load than individual branches.
Step 5: Filter replacement
The return air filter is replaced. Even if the filter appears moderately loaded, replacement at the time of cleaning establishes a clean baseline for the filter interval going forward. FreshDuct supplies the replacement filter; confirm at booking whether the replacement is included or charged separately.
Step 6: Sanitisation
A tea tree oil solution is fogged through the complete duct network using the negative pressure machine to distribute the mist. The sanitisation agent addresses residual biological contamination — mould spores and allergen proteins — that mechanical cleaning alone does not fully eliminate from duct surface materials.
Gas Service vs Duct Cleaning: Two Different Things
A common source of confusion in Melbourne is the relationship between the gas heater service and the duct cleaning service. These are two different scopes of work performed by different contractors:
Gas heater service (performed by a licensed gasfitter): inspects and services the gas heater unit — burner, heat exchanger, flue, gas valve, ignition, and controls. The heat exchanger inspection is critical for identifying cracks that could allow combustion gases (including carbon monoxide) to enter the duct airstream. Victorian regulations require this service every 2 years for rental properties. It does not include duct network cleaning.
Duct cleaning service (performed by a duct cleaning specialist): cleans the duct network — supply branches, trunk line, return air duct, and registers. Does not include the gas heater unit, burner, or heat exchanger inspection. Does not involve combustion or gas handling.
Both services are needed on a 2-year cycle for a fully maintained Melbourne ducted gas system. They can be booked separately or some companies offer combined services.