Should you pre-cool the house before a hot northerly day?

On a forecast hot northerly day, start cooling by mid-morning rather than when the house is baking at four in the afternoon. Close the windows and blinds while it's still cooler outside, set a moderate temperature and let the system hold it through the afternoon. With refrigerated air conditioning, that's almost always the more comfortable way to get through the day.

The Bureau of Meteorology describes Melbourne's typical pattern: warm northerly winds arrive first with higher temperatures, then a cold front can change conditions within minutes. Laverton averages 27 days a year at or above 30 °C and 9.4 at or above 35 °C, mostly from December to February. Those are the days this tactic is for.

A house soaks up heat all day through the roof, walls and glass, and stores it in floors, furniture and plasterboard. Once all of that has warmed through, it keeps releasing heat into the rooms for hours, which is why the house can still feel hot late at night after the change has come through. Keeping the inside cool from the morning stops that store of heat building up.

Air conditioners also work more easily when the outside air is cooler, because the outdoor unit has less trouble getting rid of heat. A unit running gently from mid-morning has an easier day than one switched on at the afternoon peak with a hot house to catch up on. On the hottest days, a system that starts from behind may never catch up.

These steps suit split systems and ducted reverse-cycle alike.

Resist dropping the set point to 18 °C when you feel hot. It won't cool the room faster; it just keeps the unit running longer and overshooting. A ceiling fan helps you feel cooler at a higher setting.

An evaporative cooler pushes outside air over wet pads and through the house, and it needs some windows or doors open so hot air can escape. You can't close up and pre-cool in the same way. But hot northerly winds come off the dry interior, and evaporative coolers work best in low humidity, so these are often their best days.

Start it early too, before the house heats, with a few windows open in the rooms you want cooled. Expect the air from the outlets to warm up as the outside temperature climbs. When the change arrives and the air turns damp, switch to fan only or turn it off and let the cooler air in.

The change can arrive within minutes. Once it's cooler outside than in, switch off and open up: windows on both sides of the house and the doors between rooms, to flush out the heat stored through the day. If the change brings strong wind or dust, wait for it to settle first.

If the change is due late or not at all, keep the bedrooms cool into the evening and let the living areas go. Deciding which rooms or zones matter after dark keeps running costs in check.

Pre-cooling only helps if the system is working. Victoria's Department of Health advises checking before extreme heat that your fan and air conditioner work, and having the air conditioner serviced if needed. Give it a proper run on a mild spring day and listen for anything new.

Clean filters, a clear outdoor unit and a drain that runs freely all help it keep up when it counts. If it struggles on the first warm day, book a service then rather than in the middle of a heatwave.