How does an evaporative cooler work?
Seeley, which makes the Breezair and Braemar coolers, describes a ducted roof unit like this. Hot outside air is drawn in, filtered and passed through moistened pads. As the water evaporates it absorbs heat from the air, so the air comes out cooler, and a fan pushes it through ducts into the rooms.
Unlike refrigerated air conditioning, it doesn't recirculate the air inside. Seeley says the cooled air has to escape, so a door or window must be left open. Swamp cooler is the American name for the same thing, and portable evaporative coolers, which Bonaire is one brand to list, use the same idea in a single room.
Evaporative or reverse cycle?
| Evaporative | Reverse cycle | |
|---|---|---|
| How it cools | Evaporates water into outside air | Moves heat out of the house |
| Windows and doors | Some must be open | Kept closed |
| Humid days | Loses effect, and Seeley doesn't recommend it for humid climates | Seeley says it copes better in humid, coastal and mixed climates |
| Winter | No heating | Heats as well |
| Water | Needs a water supply connection | No water supply |
| Servicing, as the makers advise | Seeley: after the first year, then every two years | Mitsubishi Electric: once a year |
Where it works, and where it doesn't
Dry heat is where it shines. The ACT Government says evaporative coolers are reasonably effective in the ACT's hot, dry climate but less so when it's humid, and CHOICE says they're most effective in hot, dry climates and not recommended for humid or wet ones.
The Queensland Government advises turning the water pump off when regional humidity is above 65%. With the pump off, you're left with a fan.
That's why you see so many in the south and west. In a 2021 survey of Victorian home owners in gas areas, 23% had ducted evaporative cooling, and in 2006 ducted evaporative was the most common cooling in Western Australian homes, at 32%.
The open-window rule
Getting the escape route right is the part you control. Seeley says the open window or door area should be at least twice the size of the vent, opening the ones furthest from the vents so the air crosses the house. Security vents can stand in for an open window.
Seeley has two quick tests. With the unit running, a tissue shouldn't stick to the fly screen, and at high fan a door should stay slightly open without slamming shut. If either fails, open more.
Pads, water and servicing
Seeley says its coolers should be serviced after the first year, then every two years, by the installer or an authorised service company. Bleed-system coolers also need seasonal maintenance before and after summer. See evaporative cooler service.
Pads wear out. Seeley expects Chillcel pads to last 7 or 8 years, and aspen or woodwool pads 3 or 4. More on pads and parts.
The drain water is high in mineral salts, so Seeley suggests asking a garden centre before you put it on plants.
Rules worth knowing
Victorian noise rules cover evaporative coolers too: one used for cooling mustn't be heard in a neighbour's habitable room after 11pm.
The VEU program's air conditioner categories in Victoria are for units that both heat and cool, so don't count on a VEU discount for an evaporative cooler.
For Victorian landlords, Consumer Affairs Victoria says a ducted evaporative cooler that fails and can't be repaired can be replaced with another ducted evaporative cooler that has an outlet in the main living area.
Before you buy
- Is it a bleed system or a drain-valve system, and what maintenance does each need?
- Which pads does it use, and how long does the maker expect them to last?
- Where will the drain water go?
- How many outlets, and which windows will we open when it runs?
- Is our roof suitable to carry it, and safe to service it on?
- What will heat the house in winter?
What's safe to do yourself
You can
- Open windows or doors furthest from the vents before switching on.
- Do Seeley's tissue and door tests to check the air can escape.
- On a humid day, switch to fan-only ventilation rather than cooling.
- If it blows warm, check the wall control is on cool and the water supply is turned on.
Leave to a licensed installer
- Anything on the roof. Stay off it.
- Replacing pads and cleaning the water reservoir.
- Setting the bleed rate and the water connection.
- Seasonal servicing and draining down.
What we'd do
What we'd do
If your summers are hot and dry and you're happy to keep a few windows open, an evaporative cooler is worth a serious look, alongside a heater for winter. On the coast, or anywhere summers get sticky, we'd choose reverse cycle, which heats as well. Either way, ask for an installer who looks after evaporative coolers every season, not someone who fits one now and then.
