The ideal temperature to run an air conditioner for lower running costs

The government range, and the evidence behind it

energy.gov.au's household guides are consistent on the numbers: aim for 18 to 20 degrees in winter and 25 to 27 degrees in summer. CSIRO's own advice to households lands close to the same place from the cooling side, recommending the highest setting that still feels comfortable, commonly cited as around 26 degrees during the day and a little cooler again for sleeping, then leaving the system to hold that number rather than cycling it hard. [3][15]

The reason the range matters is the cost curve attached to it, not comfort folklore. CSIRO puts a figure on the cooling side: each degree the thermostat is set lower increases energy use by roughly 5 to 10 per cent. Sustainability Victoria puts an even blunter number on the heating side: every 1 degree above the recommended 18 to 20 degree band can add around 15 per cent to the heating bill. Compounded over a Victorian winter, where a heater might run for six or eight hours most evenings, that is not a rounding error. It is the gap between a moderate quarterly bill and a genuinely uncomfortable one. [14][15]

Heating and cooling together already account for around 40 per cent of the energy used in an average Australian home, and typically more again in cooler climate zones like Victoria's. That is exactly why the thermostat setting carries so much weight in this conversation. It is not one appliance among many. For most households it is the single largest lever over the entire energy bill, bigger than the fridge, the hot water system, and the lighting combined. [3]

Hyde treats this the same way with every client: start at the government range, not below it in summer and not above it in winter, and only move away from it once there is a specific reason, a very young or elderly household member, a genuine medical need, or a room that will not hold comfort at a moderate setting no matter what. Treating a more extreme number as the default habit is the single most common way Peninsula households quietly inflate their own bills. [1][2]

Winter is the real test right now, not summer

It is worth saying plainly: this is the season where the guidance actually gets tested. 18 to 20 degrees is the recommended heating band, and the low end of it, 18 degrees, deserves to be taken seriously rather than treated as a bare minimum. energy.gov.au's winter guidance leans on layering, rugs, and warmer indoor clothing precisely so the thermostat does not have to compensate for a household still dressed for summer in the middle of July. [4][6]

Households that stay near the same setting consistently, rather than nudging it up and down through the day, tend to stop noticing the number as a compromise within a week or two. A home held steady at 18 or 19 degrees with a jumper on, rather than swung between 16 and 23 degrees depending on mood, generally feels more comfortable and costs less than the same home chasing comfort in bursts. [4][3]

Winter's load is also shaped differently to summer's. Cooling demand is short, sharp peaks on hot afternoons. Heating demand is a long, steady grind across cold mornings and evenings for months at a stretch. That steadiness is exactly why the 15 per cent-per-degree heating figure compounds so heavily over a season, and why a household running the heater at 22 or 23 degrees out of habit rather than 19 or 20 is very likely paying for it every single day of the season, not just on the coldest ones. [4][14]

None of that is an argument for a cold house. Sustainability Victoria and energy.gov.au both frame 18 to 20 degrees as the point where comfort and energy use are still in a sensible relationship, not as an austerity target. For anyone still cold at 19 or 20 degrees after reasonable clothing and basic draught-proofing, the honest next question is not 'how much higher should the heater go'. It is 'why is this specific room losing heat so fast', which is a building question rather than a thermostat question. [8][14]

Does cranking it heat or cool the room faster? No

One habit is common enough to address directly: setting the air conditioner to a far colder number than actually wanted on the theory that it will cool the room faster, then switching it off again once the room feels right. CSIRO's own guidance is blunt about this. Running a unit briefly at a very cold setting 'may feel thrifty' but is not the most efficient way to run it, because the compressor works at broadly the same rate regardless of how extreme the target is. The extreme number just tells it to keep working longer before it decides it is satisfied. [15]

The same logic runs in reverse for heating. Pushing the dial to 26 or 28 degrees on a cold morning does not make a ducted heater blow hotter air any sooner. Most systems, gas ducted or reverse-cycle, ramp up at roughly the same rate regardless of the target set. The higher number simply means the system keeps running well past the point where the room is genuinely comfortable, because it has been told to. [3][15]

CSIRO's practical alternative is to set the number that is genuinely comfortable and then leave it, letting a modern inverter-equipped system modulate its own output quietly to hold that target, rather than treating the controller as an on-off switch operated at extremes. That single habit change, on CSIRO's own advice, tends to beat the intermittent-blast approach on comfort and on cost at the same time. [15]

Humidity changes what the number on the wall actually feels like

Temperature is only half of what a body actually feels. Refrigerant-based systems, including every split, multi-split, and reverse-cycle ducted system Hyde installs, remove some moisture from the air as a side effect of cooling. That is one reason a room held at 26 degrees by a refrigerated system can feel noticeably more comfortable than the same 26 degrees on a muggy day with no mechanical cooling running at all. [3]

That dehumidifying side effect matters for coastal homes specifically. Discomfort on a sticky Peninsula afternoon is very often a humidity problem more than a pure heat problem, and a refrigerated system running at a sensible 25 to 27 degrees is usually already doing more useful work against that humidity than dropping the number further would add. [3][7]

Air movement carries just as much weight. energy.gov.au notes that a fan can make a room feel around 3 degrees cooler for a running cost of only a couple of cents an hour, so a ceiling fan paired with a 27-degree setting can feel as comfortable as a 24-degree setting with no fan at all, for a fraction of the electricity. The same logic applies loosely in reverse in winter: cutting draughts across bare skin makes a lower, cheaper heating setting feel warmer than the number alone suggests. [3]

This is the part a single number can never capture. Two homes both set to 26 degrees can feel completely different depending on humidity, airflow, and what the occupants are wearing, which is exactly why Hyde treats the government range as the start of a conversation about a specific room and a specific building, not a number to defend in isolation. [7]

Zoning is what makes the setting worth something

The setting on the wall only saves money if it is applied to the space that is actually occupied. Daikin's own product range reflects this directly: split systems are built for one room or a defined area, multi-splits let several rooms run independently from one outdoor unit, and ducted systems rely on zoning to avoid conditioning rooms nobody is using. A perfect 19-degree winter setting loses most of its value if it is quietly heating three empty bedrooms alongside the occupied living room. [10][11][12]

For a ducted system specifically, Sustainability Victoria is direct: zoning is the most efficient way to run it, closing off outlets to rooms that are not in use rather than letting the whole ductwork run at the same setting around the clock. A well-zoned ducted system holding 19 degrees in the two occupied rooms will usually cost noticeably less than an unzoned system doing the same job across the whole house. [14]

Multi-split systems make this even more direct because each indoor head can be switched on, off, or set independently. The lowest-cost way to run a multi-split in winter is rarely 'set every head to 19 degrees'. It is 'set the occupied heads to 19 degrees and leave the rest off', which sounds obvious written down but is one of the more common oversights Hyde finds in already-installed systems on service calls. [11][14]

The Zoned Energy Rating Label adds a second layer worth knowing about. Because it rates seasonal performance separately for hot, average, and cold Australian climate zones, it lets a Victorian buyer compare how a given system actually performs across a cold-climate winter rather than relying on a single generic star rating. A better-matched system makes it easier to hold a sensible setting without the unit working overtime to get there. [9]

Why reverse-cycle systems punish extreme settings even harder

For reverse-cycle systems specifically, there is a mechanical reason extreme settings cost disproportionately more, beyond the general percentage-per-degree rule. A heat pump moves heat rather than generating it, and how efficiently it can do that depends heavily on the size of the gap between the temperature it is drawing heat from and the temperature it is trying to reach. Ask it to close a small gap, heating a 12-degree morning up to 19 degrees, and it operates efficiently. Ask it to close a much larger gap, pushing that same 12-degree morning up to 24 degrees, and the compressor works proportionally harder for every extra degree of lift. [3][14]

Sustainability Victoria's framing of reverse-cycle systems as more efficient and cheaper to run than gas ducted or gas room heaters holds true across a Victorian winter on average, but it holds truest at sensible setpoints. Pushed to an unrealistic setting, a heat pump's advantage over gas narrows, because the efficiency reverse-cycle systems are known for comes from moving a modest amount of heat well, not from moving a large amount of heat under strain. [14]

This is one reason Hyde is cautious about oversized systems being run at extreme settings 'because they can handle it'. A correctly sized reverse-cycle system, run within the recommended range, will usually deliver a lower running cost over a winter than an oversized unit being pushed to a higher target on the assumption that a bigger compressor makes the number on the wall irrelevant. [12][14]

The practical takeaway for anyone with a reverse-cycle split or ducted system is that the government's 18 to 20 degree heating range is not just a comfort suggestion for that technology. It sits close to the band where the heat pump itself is working most efficiently, which is a second, independent reason to stay inside it rather than treating it as an arbitrary government number. [3][14]

Two Peninsula-specific habits worth naming

Coastal humidity is the first pattern. Even in winter, onshore weather can leave a home feeling colder and clammier at a given temperature than the same reading would feel inland, which is part of why some Peninsula households nudge the heating setting higher than the guidance suggests. The better fix is usually addressing draughts and moisture at the source rather than assuming a couple of extra degrees on the thermostat will compensate for a damp, poorly sealed room. [6][8]

Holiday homes and part-time properties are the second, and they are common across the Peninsula's coastal suburbs. It is not unusual for a weekender to be left running on a moderate setting non-stop while empty for days at a time, on the assumption that this is cheaper than reheating or recooling from scratch on arrival. For most reasonably sealed Peninsula homes, that assumption does not hold up well: a home left idle can usually be brought back to a comfortable 19 or 20 degrees in well under an hour, which tends to cost less than conditioning an empty house around the clock for a week. [4][3]

Where that logic changes is a genuinely draughty or poorly insulated older beach house, one that loses heat fast enough that reheating from cold on the coldest evenings can take longer and cost more than a modern build would. That is a building-shell problem showing up as a thermostat habit, and it is usually cheaper in the long run to fix the draughts and insulation than to keep an empty house heated at a reduced level all week. [8][6]

The honest local advice is therefore not one Peninsula-wide rule. It is knowing which kind of property this actually is, a tightly sealed modern build or an older, leakier coastal one, because that answer changes whether idle running or a full shutdown between visits is the cheaper habit for that specific home. [6][8]

The Hyde takeaway on thermostat settings

There is a real, defensible answer to what temperature saves the most electricity, and it has not changed: 18 to 20 degrees for heating, 25 to 27 degrees for cooling, treated as a target to hold rather than a number to fight against. energy.gov.au, Sustainability Victoria, and CSIRO's own testing all converge on close to the same range for the same underlying reason. It is the point where comfort and energy demand are still in a sensible relationship with each other. [3][14][15]

The number is necessary but not sufficient. Humidity, air movement, zoning, system type, and how efficiently a heat pump can actually close the gap between outside and inside temperature all shape whether that number feels comfortable or feels like a compromise. A household chasing a colder or hotter setting to fix discomfort is usually solving the wrong problem, and often making the real one, humidity, draughts, or an unzoned system, more expensive to live with rather than less. [7][8][14]

For Peninsula homeowners specifically, that means treating the government range as the default, addressing a genuinely leaky or exposed property with building fixes rather than a colder or hotter setpoint, and being honest about which kind of property is actually being run, a full-time family home, a tightly sealed renovation, or a part-time coastal weekender. Hyde would rather have that conversation properly than hand over one magic number and hope it fits every one of the very different homes across this coastline. [4][6][8]