A heat pump is already the cheapest way to heat a NZ home - but how you run it can easily double or halve what it costs. Two identical units in two identical houses can produce very different power bills purely because of settings and habits. Here is how to run yours as cheaply as possible, from the installers who set these units up every day across the Waikato.
1. The short answer
The most cost-efficient way to run a heat pump is to set it to 20-21 degrees in Heat mode, heat only the rooms you use while you are using them, and keep the filters clean. Those three habits do most of the work. Everything else in this guide - timers, fan settings, vane angles, curtains, power plans - is refinement on top of them.
None of it costs anything. Unlike upgrading insulation or replacing the unit, every tip below is a settings change or a five-minute habit, which is why it is worth getting them all right before you blame the heat pump for the bill.
2. Set 20-21 degrees, not 26
The set temperature is the single biggest lever on your running cost. Every extra degree adds roughly 10% to what the unit costs to run, because the compressor has to work longer and harder to reach and hold it. A unit set to 24 degrees costs around a third more to run than the same unit set to 21.
And cranking it to 28 when you walk into a cold room does not heat the room any faster. The compressor is already running at full output while the room comes up to temperature - the high setting just means it keeps going past comfortable, overshoots, and burns power heating air you will end up cracking a window to get rid of. Set 20-21 and leave it alone.
3. The "leave it on 24/7" myth
You will hear that heat pumps are cheapest left running all day because "maintaining a temperature costs less than reheating from cold." For a typical NZ home, that is not true. Most Kiwi houses - especially anything built before the 2008 insulation standards - leak heat quickly. Every hour the unit runs while nobody is home, you are paying to warm air that escapes through the windows, walls, and ceiling long before you get back.
For typical NZ insulation levels, it is cheaper to heat when you are home and let the house cool when you are not. Use the timer so the room is warm when you arrive - you get the comfort of the always-on approach without paying for the empty hours in between.
The exception is a very well-insulated home: a newer build with double glazing, full ceiling and underfloor insulation, and good airtightness. Those houses hold heat so well that the unit barely runs once the temperature is reached, and holding 20 degrees around the clock can cost about the same as heating twice a day. If your house was built this decade, experiment. If it is a 1970s weatherboard villa, use the timer.
4. Use Heat mode, not Auto
Auto mode sounds convenient: the unit picks heating or cooling for you. In practice it flip-flops. A sunny winter afternoon warms the lounge a degree past the set point, the unit tips into cooling mode and pulls the warmth back out, then the sun drops and it heats the same air again. You pay for both directions.
Lock the unit in Heat mode for winter and Cool mode for summer. It will only ever work in one direction, and it will simply idle when the room is warm enough instead of fighting itself. This is one of the most common fixes we make when customers ask why their power bill jumped.
5. Timers beat willpower
The expensive pattern looks like this: walk into a cold house at 6pm, hit the remote, crank it to 26 to "warm it up fast," forget to turn it back down. The cheap pattern: set the timer so the unit starts 30 minutes before you get up and 30 minutes before you get home, at your normal 20-21 degree setting.
The room is warm when you walk in, the unit has come up to temperature at its own efficient pace, and nobody is tempted to override it to a silly number. Every heat pump remote has a timer, and most newer units have Wi-Fi apps that let you switch on from the car park. Thirty minutes of lead time is plenty for a correctly sized unit.
6. Fan on Auto, vanes pointed down
Two settings people rarely touch, and both matter. Set the fan speed to Auto - the unit will run the fan hard while the room warms up, then drop it to a quiet tick-over to hold temperature. Locking the fan on Low forces the unit to run the compressor longer to move the same heat.
Then point the vanes down toward the floor. Warm air rises, so if the louvres fire it straight out horizontally from high on the wall, it pools at the ceiling while your feet stay cold and the thermostat keeps calling for more heat. Directing warm air at the floor evens the room out from the bottom up, the sensor sees the true room temperature sooner, and the unit throttles back earlier. Warm feet, smaller bill.
7. Close the envelope
A heat pump can only be as efficient as the room lets it be. Heat that escapes is heat you paid for, so the cheapest kilowatts are the ones you keep.
- Curtains at dusk: windows are the biggest heat leak in most NZ rooms. Closing curtains as the light fades can cut heat loss through the glass dramatically - thermal-backed and floor-length curtains do it best
- Close the door of the room you are heating:a 6 kW unit asked to warm the lounge does it easily; asked to warm the lounge, the hallway, and the stairwell through an open door, it runs all night
- Block the draughts: door snakes, window seals, and covering unused fireplaces all stop warm air leaking out and cold air feeding in at floor level - exactly where you just directed the warm air
8. Keep it clean
Clogged filters and dirty coils cut a heat pump's efficiency by 15-25%. The fan works harder to pull air through a mat of dust, less air moves across the coil, and the unit runs longer to deliver the same heat. It is the most common reason a unit that used to be cheap to run quietly gets expensive.
The fix costs nothing: pop the front cover, slide the filters out, and vacuum them - monthly through winter. Then book an annual professional service to clean the coils, check refrigerant and drainage, and keep the unit at close to its rated efficiency. A clean unit is also a quieter, longer-lived unit.
9. Check your power plan
The other half of the running-cost equation is what you pay per kilowatt-hour. NZ retailers now offer plans with cheaper off-peak rates overnight and in the middle of the day, and some offer a free hour of power each day. If you are on a flat-rate plan and running a heat pump every winter evening, it is worth twenty minutes on a comparison site.
Then shift what heating you can into the cheap windows: pre-warm the lounge during a free hour, run the bedroom unit's warm-up before the evening peak, or let a well-insulated home bank a little extra warmth on the cheap overnight rate. You do not need to reorganise your life around it - even moving the pre-heat timer into an off-peak window trims the bill further.
10. Get the size right in the first place
All the settings in the world cannot rescue an undersized unit. A 3.2 kW unit asked to heat a 40 square metre open-plan living area runs flat-out for hours, never quite gets there, and does it all at the least efficient end of its range. An appropriately sized unit cruises - it reaches temperature quickly, then throttles back to a sip of power.
Slight oversizing is cheap to run; undersizing is expensive forever. If you are choosing a unit now, read our guide on what size heat pump you need before you buy - it is the one running-cost decision you only get to make once.
11. What a well-run heat pump actually costs
Put the habits above together and the numbers are genuinely small. A 6 kW living-area unit running at a COP of 4 draws about 1.5 kW of electricity. At a typical 30c/kWh, that is roughly 45 cents an hour at full output - about $2.70 for six hours of evening heating, and less in practice because the unit throttles back once the room is warm.
A 3.2 kW bedroom unit at the same COP draws around 0.8 kW - roughly 24 cents an hour, or about a dollar for a four-hour evening warm-up before bed. Run badly - set to 26, in Auto mode, with dirty filters and the door open - the same units can cost double that for less comfort.
For the full breakdown by unit size, month, and how heat pumps compare with gas, wood, and panel heaters, see our guide to heat pump running costs in NZ.
Frequently asked questions
Should I leave my heat pump on all day?
For most NZ homes, no. Typical NZ insulation levels mean the heat you pay for leaks out fairly quickly, so running the unit while nobody is home wastes power. It is cheaper to use the timer so the unit starts 30 minutes before you get up or get home. The exception is a very well-insulated home - a newer build with double glazing and good ceiling and underfloor insulation - where holding a steady temperature costs little and the always-on approach can work out similar or slightly cheaper.
What temperature should I set my heat pump to in winter NZ?
Set it to 20-21 degrees in Heat mode. That is warm enough for comfort in a living area, and every degree above that adds roughly 10% to your running cost. For bedrooms overnight, 16-18 degrees is healthier for sleep and cheaper to hold. Setting the unit to 26 or 28 does not heat the room any faster - it just keeps the compressor working longer and overshoots the temperature you actually wanted.
Why is my heat pump so expensive to run?
The usual culprits are a set temperature that is too high (24-26 degrees instead of 20-21), running in Auto mode so the unit flip-flops between heating and cooling, clogged filters or dirty coils cutting efficiency by 15-25%, heating rooms with open doors and bare windows so the warmth escapes, or an undersized unit running flat-out to keep up. Fix the settings and the filters first - they cost nothing - then look at the room and the sizing.
Is it cheaper to run a heat pump on low all day or high in bursts?
Neither extreme wins. The cheapest pattern for a typical NZ home is a normal set temperature (20-21 degrees) run only during the hours you are actually home, started 30 minutes early on a timer. Running on low all day pays to heat an empty house; blasting on high in short bursts makes the unit work at its least efficient output and usually overshoots. A modern inverter unit is most efficient when it warms the room at a steady setting and then throttles back to hold it.
Does servicing really lower running costs?
Yes, measurably. Clogged filters and dirty coils force the fan and compressor to work harder for the same heat, cutting efficiency by 15-25%. Vacuuming the filters monthly through winter is free and takes five minutes. An annual professional service cleans the coils, checks refrigerant and drainage, and keeps the unit running at close to its rated efficiency - which is the efficiency you paid for when you bought it.
Should I use Auto mode on my heat pump?
In winter, no - use Heat mode. Auto mode lets the unit decide whether to heat or cool, and on a sunny NZ winter afternoon it can tip into cooling the very room you warmed up that morning, then heat it again when the sun drops. That flip-flopping wastes power fighting itself. Lock the unit in Heat for winter and Cool in summer, and you will always know exactly what it is doing.
