Best temperature for air conditioning

Why twenty-four degrees is the summer standard

Setting your air conditioner to 24°C during the warmer months is the most effective way to balance comfort with running costs. Many homeowners make the mistake of cranking the thermostat down to 18°C or 20°C as soon as they walk into a hot house, believing this will cool the room faster. In reality, an air conditioner delivers air at the same temperature regardless of the set point; the thermostat simply tells the compressor when to stop. By setting the unit to 24°C, you allow the system to reach a sustainable operating state sooner, which is particularly important for modern inverter systems that are designed to ramp down their power consumption once the target is met.

The physics of cooling relies on the temperature difference between the indoor air and the outdoor environment, often referred to as the 'delta T'. Most residential systems are engineered to handle a temperature drop of about 10°C to 12°C below the ambient outdoor temperature efficiently. When the mercury hits 35°C outside, a 24°C internal setting is well within the system's efficient operating range. If you force the unit to try and reach 18°C on that same day, the compressor will likely run at 100% capacity indefinitely, never reaching the target and significantly increasing wear and tear on the mechanical components.

Energy consumption is the primary driver for the 24°C recommendation. Industry data suggests that for every degree you lower the thermostat in summer, you increase the electricity usage by roughly 10%. Over a long summer, the difference between a home kept at 21°C and one kept at 24°C can represent hundreds of dollars on a utility bill. If 24°C feels slightly too warm, we suggest using a ceiling fan in conjunction with the split system air conditioning to improve air movement, which can make the room feel 2°C to 3°C cooler without actually lowering the thermostat.

Heating your home efficiently during winter

When the season shifts and you switch your reverse cycle system to heating mode, the ideal temperature setting is 20°C. In Australia, the National Construction Code and various energy efficiency bodies support this benchmark because it provides enough warmth to maintain health and comfort without overworking the heat pump. Just as with cooling, the 5% to 10% rule applies to heating: every degree you raise the thermostat above 20°C will noticeably increase your energy consumption. A setting of 24°C in winter is not only expensive but often unnecessary if the home is properly sealed and insulated.

Reverse cycle air conditioning is significantly more efficient than portable electric bar heaters or gas heating because it moves heat rather than creating it. However, its efficiency is still tied to the outdoor ambient temperature. In a dry inland climate where overnight temperatures drop toward zero, the outdoor unit must work harder to extract heat from the air. Maintaining a steady 20°C allows the system to operate within its most efficient thermal cycle. If you find 20°C too cool, prioritising draught-proofing around doors and windows is a more cost-effective solution than turning up the heat.

Construction materials play a massive role in how well your home retains this heat. A home with double-glazed windows and high R-value ceiling insulation (typically R4.0 or higher) will hold onto that 20°C warmth much longer than an uninsulated weatherboard cottage. If your home has high thermal mass, such as internal brick walls or a concrete slab, the air conditioner doesn't have to work as hard to maintain the temperature once the mass has been warmed. We find that many modern builds with a 7-star energy rating can maintain comfortable temperatures with very little mechanical intervention if the thermostat is managed correctly.

How humidity affects your thermostat settings

Temperature is only one part of the comfort equation; the other is relative humidity. In a humid coastal climate, the 'apparent temperature' or how hot you actually feel is often much higher than what the thermometer shows. This is because high humidity prevents sweat from evaporating off your skin, which is the body's natural cooling mechanism. A home in Darwin faces a very different challenge than one in a dry desert zone. In tropical environments, the air conditioner must perform 'latent cooling'—which is the removal of moisture—before it can effectively lower the 'sensible' air temperature.

Most modern systems have a 'Dry Mode' specifically designed for high-humidity days. This mode prioritises moisture removal by running the indoor fan at a lower speed, allowing the air to spend more time in contact with the cold evaporator coil so more water can condense and be drained away. While 24°C might feel perfect in a dry heat, you might find you need to lower the setting to 23°C or use Dry Mode during a Brisbane summer to achieve the same level of comfort. Removing the 'mugginess' from the air often allows you to keep the thermostat higher than you otherwise would.

It is also worth considering the dew point. If you set your air conditioner too low in a very humid environment, you risk creating condensation on the external surfaces of the indoor unit or around the supply grilles of ducted air conditioning systems. This can lead to moisture damage or mould growth over time. Keeping the thermostat at a moderate 24°C helps ensure the temperature of the internal components doesn't drop below the dew point of the surrounding air, protecting your home's structure and air quality.

The role of building materials in temperature control

Your home's physical structure dictates how hard your air conditioner has to work to hit your target temperature. For example, a dark tiled roof can reach temperatures of 65°C or more on a summer afternoon, radiating immense heat into the roof cavity. If your ductwork is located in this space, the air inside the ducts is being heated before it even reaches your rooms. In these scenarios, setting the thermostat to 24°C is a practical necessity; the system may struggle to achieve anything lower because of the heat gain through the ceiling and ducting.

Australian building standards have improved, but many older homes lack the thermal breaks required for high efficiency. Brick veneer homes with large west-facing windows are notorious for 'heat soak,' where the bricks absorb solar energy all day and continue to radiate heat into the house long after the sun has gone down. If you live in such a home, we recommend starting the air conditioner earlier in the day at 24°C to 'pre-cool' the thermal mass, rather than waiting until the house is 30°C and trying to bring it down rapidly. This prevents the heat from becoming trapped in the internal walls and furniture.

Lightweight cladding and Colorbond roofing react much faster to temperature changes. While they heat up quickly, they also cool down quickly once the sun sets. For these homes, the air conditioner can be very responsive, but it relies heavily on the quality of the wall insulation. If you find that your system is constantly cycling on and off to maintain 24°C, it may be a sign that the home's 'envelope' is leaking air. Checking the seals on your external doors and ensuring your wall batts haven't slumped can make a significant difference in how easily your system maintains its set point.

Setting the right temperature for sleep

Sleeping requires a different approach to temperature management. The human body's core temperature naturally drops as part of the circadian rhythm, and a room that is too hot or too cold can disrupt this process. For most people, the ideal sleeping temperature is between 20°C and 22°C. While this is lower than the recommended daytime summer setting of 24°C, the outdoor ambient temperature is also lower at night, meaning the system doesn't have to work as hard to maintain this cooler environment.

Using a 'Sleep Mode' or a programmable timer is a highly effective way to manage night-time settings. Sleep Mode typically starts at your preferred setting and then gradually increases the temperature by 1°C or 2°C over several hours. This follows your body's natural cooling cycle and prevents you from waking up feeling too cold in the early hours of the morning. It also reduces the noise of the outdoor unit, which is a consideration if your compressor is located near a bedroom window or a neighbour's fence.

In a well-insulated room, a split system can often be turned off once the occupants are asleep, provided the room has been cooled effectively beforehand. However, in a home with high heat retention, the unit may need to run on a low fan setting all night. If you are using a ducted system, ensure the zones are configured so that you aren't wasting energy cooling the living areas and kitchen overnight. Focusing the airflow only on the occupied bedrooms allows the system to reach the 22°C target quickly and stay there with minimal power draw.

Optimising performance through sensor placement

The accuracy of your thermostat is only as good as the sensor that feeds it data. In many ducted systems, the main sensor is located on the wall controller, often in a hallway. If this hallway is naturally cooler than the north-facing lounge room, the air conditioner may switch off before the lounge room reaches 24°C. Conversely, if the sensor is located near a heat source like a kitchen or in direct sunlight, it will 'think' the house is much hotter than it is, causing the system to over-cool the rest of the home and waste energy.

For split systems, the sensor is usually located inside the indoor head unit. Because heat rises, the air at the ceiling is always warmer than the air where you are sitting. This is why a split system set to 24°C might actually cool the lower half of the room to 22°C. Understanding this 'stratification' helps you choose the right setting. If you feel too cold at 24°C, try 25°C; the sensor is just reacting to the air at its specific height. We often find that a quick air conditioning service to clean the sensors and filters can resolve issues where a system seems to be 'drifting' from its set temperature.

Finally, the use of smart controllers and Wi-Fi modules has changed how we interact with these settings. You can now monitor the actual temperature of your home remotely and adjust it before you arrive. This allows for a more nuanced approach than just leaving the system on all day. If the house is empty, you might let it rise to 28°C, then use your phone to bring it back to 24°C half an hour before you get home. This 'active management' is the most modern way to ensure you never sacrifice comfort for the sake of your electricity bill.