Keeping a west-facing home cool on hot afternoons

A west-facing room takes low afternoon sun straight through the glass at the same time the outside air peaks. The Bureau of Meteorology describes a typical Melbourne pattern: warm northerly winds arrive first with higher temperatures, then a cold front can change conditions within minutes. Until that change comes through, the west side of the house is soaking up heat.

Laverton averages 27 days a year at or above 30 °C and 9.4 days at or above 35 °C, mostly from December to February. Those are the afternoons when a west-facing lounge in Altona, or a bedroom on the west side of a Point Cook double-storey, turns into an oven.

Heat that gets in during the afternoon is also stored in the walls, slab and furniture, so the room stays warm well into the evening. That is why most of the fix is about keeping heat out, not just pumping it out once it is in.

Shading outside the window stops the sun before it turns into heat in the room. Once sunlight is through the glass, an internal blind can only slow it down. External roller blinds, awnings, adjustable louvres and shade sails all work. On west windows, vertical shading such as an external blind does more than eaves, because the afternoon sun comes in low under them.

Planting helps over time. A deciduous tree, or a vine on a pergola, shades in summer and lets the winter sun through. In newer estates in Tarneit, Truganina and Wyndham Vale, where gardens are young, external blinds give quicker results while the trees grow.

Inside, light-coloured, close-fitting blinds or curtains with a reflective backing are the next best thing. Close them before the sun reaches the glass, not after the room is already hot.

Big sliding doors and picture windows on a west wall let in a lot of afternoon heat. If you are replacing windows, ask about glazing with better heat control for that elevation. Retrofit films can cut heat gain through existing glass, though they also cut some daylight and not every film suits every glass type, so get a glazier's advice.

Renters should ask the rental provider before any external change, but removable internal blinds, reflective blockout curtains and door seals are easy to fit and take with you when you move.

On a forecast hot day, close the west blinds and windows by late morning. Keep the house shut through the afternoon, then open up once the cool change arrives or the air outside drops below the temperature inside. A cross breeze through the house after the change does a lot of work for nothing.

Pre-cooling is easier on the system than recovering a room that has reached 32 °C. Start the air conditioning before the afternoon peak and keep the set point at 24 to 26 °C. The Victorian Government suggests that range for cooling living areas and says each degree below it adds around 10% to running costs.

A ceiling fan doesn't lower the air temperature, but air moving across your skin makes the room feel cooler. With a fan running, 26 °C is far more comfortable, which lets the air conditioner work less. A fan draws a small fraction of the power an air conditioner does.

In a west bedroom that holds its heat into the night, a quiet DC fan on low can let you switch the cooling off at bedtime. Turn fans off when you leave the room, since they cool the people in it, not the room itself.

Aim the indoor unit's airflow at where people sit, not along a wall of hot glass. A west-facing open-plan living area needs a unit sized for its afternoon load, which is often well above what the floor area alone suggests.

Outdoor units lose capacity in hot air. One mounted on a west wall in full afternoon sun, or squeezed into a narrow side passage breathing its own exhaust, struggles exactly when you need it most. Where there is a choice, a shaded south or east wall with clear space around the unit works better. Never box in or cover an outdoor unit in a way that blocks its airflow.

Before summer, run the cooling on a mild day and clean the filters. Victoria's health department advises checking before extreme heat that your fan and air conditioner work, and getting the air conditioner serviced if needed.

In a double-storey home, a west-facing bedroom upstairs gets the afternoon sun on its wall and heat coming down through the ceiling from the roof. Good ceiling insulation makes a real difference, and old downlights that need a ring cut in the insulation leave holes in that blanket.

A ducted system with a separate zone for the upstairs bedrooms, or a wall split in the worst room, often solves what one central system can't. Shading that west window first may mean a smaller unit does the job.