Evaporative cooling is Melbourne’s second-most-common cooling system type, highly effective in the city’s relatively low-humidity summer climate. Unlike gas heating or refrigerated cooling systems, evaporative coolers use water — which introduces specific maintenance requirements around mineral scale, biological growth, and seasonal shutdown that don’t apply to other system types. Understanding these requirements prevents the most common evaporative cooling problems: musty first-start smells, reduced cooling performance, and mould in the duct network.
How Melbourne Evaporative Cooling Systems Get Contaminated
Evaporative coolers are open systems — they draw in large volumes of outdoor air and introduce water into that airstream. This creates contamination pathways that sealed refrigerated systems do not have.
Mineral scale from Melbourne water
Melbourne’s water supply contains dissolved minerals. As water evaporates from the cooling pads, these minerals are left behind as white or grey mineral scale. Over a season, scale builds up on the pad surface and on the internal water distribution manifold and tray. Heavy scale reduces water absorption by the pads (reducing cooling effect) and can block the water distribution nozzles.
Biological growth in the water system
The warm, moist environment inside an evaporative cooler — particularly the internal water tray — is ideal for algae, bacteria, and mould growth. During the cooling season, continuous water flow through the system limits growth to manageable levels. When the system is shut down for winter with water remaining in the tray, biological growth accelerates in the stagnant water. By the following spring, the tray can have significant biological contamination that is then aerosolised into the home on first-start.
Outdoor air contaminants
Evaporative coolers draw in outdoor air, meaning that pollen, dust, and bushfire smoke particles entering through the system are present in significantly higher concentrations than in a closed refrigerated system. During Melbourne’s spring pollen season and in smoke events, this can substantially increase allergen and particle load in the home. See our guides on duct cleaning after bushfire smoke and air ducts and allergies in Melbourne.
Full Service Scope for Melbourne Evaporative Cooling
Roof unit service
Pad inspection and replacement: The cooling pads are removed and inspected. Pads with structural integrity and only light mineral scale can be hosed clean and reinstalled. Pads with significant scale hardening, biological growth, or physical deterioration are replaced. See the FAQ below for pad replacement intervals in Melbourne.
Internal water tray cleaning: The water tray at the base of the unit is drained, scrubbed to remove mineral scale and biological residue, and rinsed thoroughly. A mild descaling solution (white vinegar or commercial descaler) dissolves mineral scale. The tray is inspected for corrosion in older metal-tray units.
Water distribution system: The water distribution manifold and nozzles are checked for blockage and flow balance. Blocked nozzles cause dry sections in the cooling pad — areas where water does not reach, leaving the pad dry and ineffective for that section.
Blower and motor inspection: The blower fan is inspected for debris accumulation and the motor is checked for bearing noise and electrical connection security. A blower clogged with debris draws more current and moves less air.
Duct network cleaning
The duct cleaning scope for an evaporative system is the same as for gas heating: negative pressure extraction of all supply branches and trunk line, rotary brush cleaning of accessible runs, register removal and cleaning, and sanitisation fogging. The larger register sizes typical of evaporative systems (to accommodate the higher air volumes) are a practical difference but do not change the cleaning approach.
Seasonal Shutdown: The Most Important Evaporative Maintenance Step
Proper seasonal shutdown is arguably the single most important maintenance step for Melbourne evaporative cooling owners. It takes 30 to 60 minutes and prevents the winter biological contamination that produces musty first-start smells the following season.
At end of cooling season (March to April in Melbourne): turn off the water supply to the unit, run the blower for 30 minutes without water to dry the pads and internal surfaces, drain the water tray completely, clean the tray of any residual scale and debris, and cover the unit outlet with a purpose-made evaporative cooler cover to prevent debris and bird entry through winter.