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When the first heatwave hits, the temptation is to punch the heat pump down to 18 and wait for relief. It is the summer version of the winter mistake of cranking it to 28, and it costs you the same way: a big power bill and a house that is colder than it needs to be. The right cooling temperature keeps you genuinely comfortable and your running costs sensible, and it is higher than most people think. Here is the number to set, and why.
Set your heat pump to around 23 to 25 degrees for cooling in summer, not 18. A good guide is roughly 6 to 8 degrees cooler than it is outside, which feels comfortable without a jarring cold shock or a huge bill. Setting it colder does not cool the room any faster, it just runs longer and costs more, since each degree lower adds meaningfully to your energy use. For sleep, a slightly warmer setting or sleep mode works well.
Here is how to set your cooling temperature for comfort and cost.
For cooling, a setting of around 23 to 25 degrees keeps most people comfortable through an Auckland summer. Rather than fixating on a single figure, a reliable approach is to aim for about 6 to 8 degrees cooler than the outdoor temperature. On a 30-degree day, that means a house at around 23 to 24 feels pleasantly cool without being a shock every time you walk in from outside, and without the unit straining to hold an unnaturally low temperature. The low-to-mid twenties is the sweet spot, just as the low twenties is for heating in winter.
Here is the summer version of the myth worth killing. Setting the heat pump to 18 does not cool the room any faster than setting it to 24. A heat pump runs at full output to reach whatever temperature you set, and a lower number does not make cool air arrive sooner, it just means the unit does not stop at 24, so it keeps running, overshoots to a colder-than-needed room, and costs you more. If you want the room cool quickly, the fan speed helps far more than a lower temperature. Set the temperature you actually want to feel, and the heat pump gets there just as fast.
The reason the setpoint matters so much is cost. Just as in heating, every degree counts, and asking for a room several degrees colder than necessary adds noticeably to your energy use. Dropping from a sensible 24 to an unnecessary 19 is not a small change, it is a meaningfully bigger bill for cooling you do not need, and often for a house that ends up uncomfortably cold. Nudging the setpoint up a degree or two is one of the easiest summer savings there is, and it feeds directly into your overall running costs. A jumper is a winter thing, but the summer equivalent is simply not overcooling.
Sometimes the problem is not the temperature at all, but the humidity, and setting a low cooling temperature is the wrong tool. On muggy Auckland days when the air feels heavy and clammy but is not scorching, dry mode removes moisture with far less energy than cranking the cooling, and often that is all it takes to feel comfortable. So before you drop the cooling setpoint low, ask whether the room is genuinely hot or just damp, and if it is damp, dry mode or better ventilation is the smarter, cheaper answer.
Bedrooms are their own case at night. You do not need to hold a daytime cooling temperature to sleep well, and running the unit hard and cold all night is both wasteful and often uncomfortable. A slightly warmer setting than you would use during the day is usually plenty for good sleep, and many units have a sleep or econo mode that gently eases the temperature over the night for comfort and efficiency. The timer is useful too, cooling the bedroom before you turn in and then easing off, so you are not paying to run it cold until morning.
If you have the temperature set sensibly and the room still will not cool, the setpoint is not the problem. A dirty filter choking the airflow is a common culprit, so start there with a clean, as covered in our maintenance guide. A unit that is undersized for the room will also struggle on the hottest days no matter how low you set it, and an older, less efficient model costs more to achieve the same cooling. If yours cannot keep up despite a sensible setting and clean filters, it may be worth comparing more efficient heat pump options.
The right cooling temperature is the one that keeps you comfortable without freezing the house or the budget, and for an Auckland summer that is the low-to-mid twenties, not 18. Set it sensibly, lean on dry mode for humidity, and ease off at night, and you stay cool all summer without the bill shock.
Varcoe has kept Auckland homes comfortable in every season since 1975. If your heat pump cannot cool comfortably at a sensible setting, get in touch, call us on 0800 088 888, or email info@varcoe.co.nz.
Around 23 to 25 degrees, not 18. A good guide is roughly 6 to 8 degrees cooler than the outdoor temperature, which feels comfortable without a cold shock or a large bill. The low-to-mid twenties is the sweet spot for most people.
No. A heat pump runs at full output to reach whatever you set, so 18 does not cool faster than 24, it just overshoots, runs longer and costs more. If you want faster cooling, increase the fan speed rather than lowering the temperature.
Yes. Just as with heating, each degree lower adds noticeably to your energy use, so cooling to an unnecessary 19 instead of a comfortable 24 means a meaningfully bigger bill. Nudging the setpoint up a degree or two is an easy summer saving.
A slightly warmer setting than during the day is usually plenty for good sleep, and many units have a sleep or econo mode that eases the temperature overnight for comfort and efficiency. The timer can cool the room before bed and then ease off.
If the room is genuinely hot, use cool mode at a sensible temperature. If it is muggy and clammy but not especially hot, dry mode removes the humidity with far less energy and is often all you need to feel comfortable, making it the cheaper choice on damp days.
Usually a dirty filter choking airflow, a unit undersized for the room, or the space heating faster than it can cope due to sun and open doors. Clean the filters, help the house stay cool, and if it still cannot keep up, the unit may be too small or too old.
If your heat pump cannot cool well without being cranked cold, our Auckland team can check it out.
