By Julie Curnow

Want To Boost Your Evaporative Air Conditioner’s Effectiveness? Your Power Bill Will Thank You!


Using evaporative air conditioning (also known as evaporative coolers) is a common whole of home cooling system because of its low purchase price and low running cost.


But you can make it work more efficiently and reduce its running cost further by adding a security relief vent and two roof space ventilators (“whirly birds”).These items cost nothing to run and a couple of hundred dollars to purchase. If you are good at DIY you can install them yourself, as per the manufacturers’ instructions and specifications.

If you can’t get a security relief vent use the largest butterfly damper with the control knob removed and attach it to the relevant sized outlet. Do not attach it to ducting – it needs to vent straight into the roof space.

How to boost your evaporative air conditioner’s performance and reduce its running cost

  • Close all your external doors and windows
  • Open your internal doors (to allow unencumbered airflow to the security relief vent)
  • Turn your evaporative air conditioner on to cooling on a low setting. 
  • Run your system this way for long enough for your roof space to achieve ambient temperature.
  • Afterwards open your doors and windows and run your evaporative air conditioning as normal.

You need to keep the exterior doors and windows closed so that air pressure builds up pushing the security relief vent open and pushing the cooled air into the roof space.

On a hot summer’s day we recommend you run your air conditioning like this for two sessions of half an hour. First once the roof space has heated up (outside temperature hits 28 degrees C / 82 degrees F) and the second time when the maximum outside temperature is reached.
In spring one half hour session should suffice at the hottest time of day.

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How it works

  • Hot air rises and is trapped in your roof space. Your roof space can be up to 30oC (86Fahrenheit)  hotter than your living areas on a hot day.
  • The security relief vent allows cooled air into your roof space and displaces the hot air circulating there.
  • The hot air in your roof is dispelled outside via the roof ventilation system.



The cooler air in the roof space means that there is less heat load on your home so:

  • your ideal temperature in your home is reached quicker and maintained easier. and / or 
  • you don’t need to turn the evaporative air conditioning up to such a high setting. 

A lower setting means:

  • less electricity to run the cooler, 
  • less load and thus less wear and tear on the evaporative cooler and the ducting,
  • less noise as lower air flow, and
  • less air turbulence.

How much difference will it make?

Well the amount of difference it makes to your evaporative air conditioning’s performance and running costs will depend on the insulation in your roof space.
If your home is poorly insulated more heat will come into your living areas than if your home is well insulated.
So a poorly insulated home will reap greater benefits than a well insulated home.


You can use our Calculator to see how often you use your Air Conditioner


Where to place the security relief vent?

The security relief vent needs placing centrally in the home to maximise the air flow it receives. A hallway is a good location.

This article was written by Don Curnow owner of Air and Water Residential, Perth Western Australia. Don has 18 years experience in the air conditioning industry in Perth and Melbourne. Air and Water Residential currently supply and install a security relief vent and two roof ventilators with each evaporative air conditioning system they supply and install.

*The information and advice offered here is a guide, please always check the manufacturers’ instructions of your product.

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