Does evaporative cooling work in Perth?

Yes on dry days, which Perth has plenty of, and poorly on humid days, which Perth's coastal suburbs get most summer afternoons once the sea breeze arrives. It works best east of the coastal plain and in homes where windows can stay open.

Is evaporative cooling cheaper than air conditioning?

Much cheaper to run, at roughly 10 to 20 cents an hour against $1.30 to $2.00 for whole-home refrigerated cooling, and cheaper to install. It is not cheaper if you also need heating, since it provides none.

Can you run evaporative cooling with windows closed?

No. The cooled air must exit the house or the unit just raises humidity and pressure. Windows or doors need to be open in the rooms you are cooling, which affects security, noise and dust.

Which is better for allergies, evaporative or refrigerated?

Refrigerated. It recirculates and filters indoor air and lowers humidity, which limits mould and dust mites. Evaporative brings in outside air with its pollen and humidifies the house.

How much water does an evaporative air conditioner use?

Roughly 20 to 30 litres an hour on a hot day, plus periodic dump cycles to flush salts. Over a Perth summer that is typically several kilolitres, a small cost in dollars but worth knowing in a dry climate.

Evaporative vs Refrigerated Air Conditioning in Perth: What Actually Works in a Perth Summer

Perth is one of the few Australian cities where this is a genuine question. Here is how each performs on the days that matter.

By Nik Jankovic, owner and lead technician at NCA HVAC. ARC licence AU069671Published 7 September 20267 min read

Short answer

Refrigerated reverse-cycle is the better choice for most Perth homes because it cools reliably on every day of summer, including humid sea-breeze afternoons, and it heats in winter. Evaporative cooling costs a quarter to a third as much to run and suits Perth's dry easterly days well, but it loses effectiveness above about 50 percent humidity, cannot heat, needs windows open, and struggles in the coastal suburbs where the Fremantle Doctor arrives most afternoons.

Key takeaways

Evaporative works by adding moisture to air. It performs best when the air is dry and poorly when humidity is already high.
Perth's hottest days are often dry easterlies, where evaporative shines, but the afternoon sea breeze raises humidity and cuts its output.
Refrigerated costs three to four times more per hour to run but delivers a set temperature regardless of humidity and also heats.
Evaporative cannot be used with the house closed up and does not filter pollen or smoke effectively.
In Perth's eastern suburbs and hills, evaporative is a defensible choice. West of the freeway, refrigerated is usually the right call.

How each system cools

An evaporative cooler pulls hot outside air through wet filter pads. Water evaporates into the air, absorbing heat, and a large fan pushes the cooled, humidified air through ceiling ducts. The air must escape through open windows or doors, so the house is under slight positive pressure and constantly flushed with outside air.

A refrigerated system, whether split or ducted reverse-cycle, moves heat from inside the house to the outdoor unit using a refrigerant cycle. It recirculates indoor air, dehumidifies as it cools, holds a set temperature, and reverses in winter to heat.

Why humidity decides it in Perth

Evaporative cooling can only lower air temperature toward the wet-bulb temperature, which depends on humidity. At 38 degrees and 20 percent humidity, a typical dry Perth easterly, a good evaporative unit delivers air around 24 to 26 degrees, which feels excellent. At 32 degrees and 60 percent humidity, a classic afternoon after the sea breeze comes in, the same unit delivers air around 27 to 28 degrees while adding more moisture to an already sticky room.

Perth's summer pattern is a hot, dry morning with easterly winds followed, on most days, by the south-westerly sea breeze in the afternoon. Coastal suburbs from Fremantle to Joondalup get the breeze earlier and more humidly. Suburbs east of the Darling Scarp and out toward Midland and the hills stay drier for longer. That geography, more than anything else, decides whether evaporative will satisfy you.

Evaporative vs refrigerated: comparison for Perth

Factor	Evaporative	Refrigerated reverse-cycle
Cooling on dry 38 degree easterly	Very good	Very good
Cooling on humid sea-breeze afternoon	Poor to fair	Very good
Temperature control	No setpoint; depends on outside conditions	Holds a set temperature
Heating in winter	None	Yes, efficient reverse-cycle heating
Running cost per hour (ducted, whole home)	$0.10 to $0.20 plus 20 to 30 L water	$1.30 to $2.00 with all zones open
Installed cost (whole home)	$4,000 to $7,000	$8,000 to $15,000
Windows and doors	Must be open	Must be closed
Air quality	Brings in outside air, pollen and smoke	Filters recirculated air; better for allergies
Maintenance	Pad replacement every 3 to 5 years, water treatment, winter cover	Annual service, filter cleaning
Bushfire smoke and dust days	Unsuitable	Fine
Resale appeal in Perth	Neutral to slightly negative	Positive

Running cost: the case for evaporative

This is where evaporative wins clearly. A ducted evaporative cooler draws only a fan motor and a small pump, typically 300 to 600 watts, which is 10 to 20 cents an hour at Perth's tariff. It also uses 20 to 30 litres of water an hour on a hot day, which is only a few cents but adds up to several kilolitres over a summer. A ducted refrigerated system cooling the whole house draws 4 to 6 kW, which is $1.30 to $2.00 an hour. Over a summer of heavy use, the difference can be several hundred dollars.

That gap narrows when refrigerated is zoned properly. Cooling two rooms on a ducted refrigerated system, or running a single split, costs 40 to 70 cents an hour. And evaporative has no winter benefit, so a home with evaporative cooling still needs a separate heating solution.

Comfort: the case for refrigerated

Refrigerated cooling delivers the temperature you set, with lower humidity, every day of summer. Evaporative delivers whatever the outside air allows, and on the sticky days you cannot tighten it further. Refrigerated lets you shut the house up, which also keeps out dust, pollen and bushfire smoke. Evaporative requires open windows, which brings all three in and makes security a consideration overnight.

Who should choose evaporative in Perth

Homes in the eastern suburbs, foothills and hills where afternoon humidity stays lower.
Households that prioritise running cost over guaranteed comfort on the worst days.
Larger, older homes with high ceilings and good cross-ventilation that suit flushing with outside air.
Anyone who already has separate heating, such as a wood heater or gas, and only needs summer cooling.

Who should choose refrigerated

Coastal and western suburbs where the sea breeze arrives early and humid.
Anyone who wants heating from the same system.
Allergy and asthma households, and anyone affected by smoke or dust days.
Homes where windows must stay closed for security, noise or a pool fence.
Owners thinking about resale in the next decade.

Frequently asked questions

Does evaporative cooling work in Perth?: Yes on dry days, which Perth has plenty of, and poorly on humid days, which Perth's coastal suburbs get most summer afternoons once the sea breeze arrives. It works best east of the coastal plain and in homes where windows can stay open.
Is evaporative cooling cheaper than air conditioning?: Much cheaper to run, at roughly 10 to 20 cents an hour against $1.30 to $2.00 for whole-home refrigerated cooling, and cheaper to install. It is not cheaper if you also need heating, since it provides none.
Can you run evaporative cooling with windows closed?: No. The cooled air must exit the house or the unit just raises humidity and pressure. Windows or doors need to be open in the rooms you are cooling, which affects security, noise and dust.
Which is better for allergies, evaporative or refrigerated?: Refrigerated. It recirculates and filters indoor air and lowers humidity, which limits mould and dust mites. Evaporative brings in outside air with its pollen and humidifies the house.
How much water does an evaporative air conditioner use?: Roughly 20 to 30 litres an hour on a hot day, plus periodic dump cycles to flush salts. Over a Perth summer that is typically several kilolitres, a small cost in dollars but worth knowing in a dry climate.