How warm should you set your heat pump in NZ winter?
The short answer is 20 to 21 degrees for living areas during the day, and 18 to 19 degrees in bedrooms overnight. That is what EECA recommends, and it lines up with the WHO's minimum healthy indoor temperature of 18C. Under the Healthy Homes Standards, landlords must install a fixed heater capable of reaching 18C in the main living room based on the coldest morning expected in that climate zone, which is the same target temperature.
Cranking the thermostat to 24C does not heat the room faster, it just tells the heat pump to keep going past the temperature you actually want. Each additional degree above 20C adds roughly 10 percent to the unit's running cost over the day.
The settings that matter
- Mode: Heat (or Auto, if your unit picks heat correctly).
- Temperature: 20-21C in the living room, 18-19C in bedrooms. Lower if you are out of the room.
- Fan: Auto. The unit ramps up at startup and throttles down once the room reaches setpoint. Locking it on High wastes energy and is noisier.
- Direction: Vanes pointed downward in winter so warm air falls into the room rather than skimming the ceiling.
- Timer: Set it to come on 20-30 minutes before you wake or get home. It is far cheaper to pre-warm than to blast a cold room.
Leave it on, or turn it off?
The right answer depends on the building. In a well insulated home (post-2010 build, or retrofitted with ceiling and underfloor insulation), turn it off when you leave. The room will hold heat for a few hours and you will not be paying to maintain temperature in an empty house.
In a poorly insulated villa, the calculus changes. The walls and floor are continually pulling heat out of the room, so coming home to a cold house and trying to bring it up 8C uses more energy than holding it at a lower 16-17C all day. A timer that holds 16C while you are out and bumps to 20C before you arrive is usually cheapest.
What about overnight?
Most people are warmer with the heat pump off in the bedroom and good bedding, than with it running and the room over-warm. If you do run it overnight, set 17-18C and use the sleep timer, which lowers the setpoint by a degree or two through the night.
Real costs at 20C versus 24C
A typical 2.5 kW heat pump in Christchurch (current MBIE retail rate around 38.5 c/kWh, COP roughly 3.7 in winter) running 8 hours a day:
- Targeting 20C in a moderately insulated room: about 0.7 kW electrical input averaged across the run, or $2.15 per day ($66/month).
- Targeting 24C in the same room: closer to 0.95 kW averaged, or $2.95 per day ($89/month).
That is $22 a month, $130 across a four-month winter, for being four degrees warmer than necessary. Most people sleep better and feel less stuffy at 20-21 anyway.
The cost of each degree, laid out
The "about 10% per degree" rule is easier to trust when you can see it. Taking the same Christchurch unit (2.5 kW heat output, winter COP ~3.7, 38.5 c/kWh) running 8 hours a day, here is roughly what each target temperature costs over a month:
| Setpoint | Avg electrical draw | Per day | Per month |
|---|---|---|---|
| 18C | ~0.58 kW | ~$1.78 | ~$54 |
| 20C | ~0.70 kW | ~$2.15 | ~$66 |
| 22C | ~0.82 kW | ~$2.53 | ~$77 |
| 24C | ~0.95 kW | ~$2.95 | ~$89 |
The exact draw depends on how leaky your room is - a well-sealed room sits near the bottom of each band, a draughty villa near the top - but the shape holds everywhere: the cost climbs steadily with the setpoint because the unit has to maintain a bigger gap between inside and outside. Colder regions pay more for the same degrees. The same exercise in Dunedin or Invercargill, where winter COPs sit nearer 3.3, pushes every row up by roughly 10-15%.
The mistakes that cost the most
Thermostat setting aside, a few habits keep adding to the bill without making the room any more comfortable:
- Treating the thermostat like a throttle. Setting 28C to "warm up faster" does nothing - the unit is already running flat out at startup. It just overshoots the temperature you wanted and keeps paying for it.
- Locking the fan on High. Auto lets the unit ramp up to reach setpoint and then throttle down to hold it. Forcing High keeps it working harder than it needs to, and it is noisier.
- Skipping the filters. A month of dust chokes airflow and can cut the effective COP by 10-25%, so the same warmth costs more. Vacuum them monthly through winter.
- Vanes pointing up. Warm air rises, so aiming the louvres at the ceiling leaves the floor cold and tempts you to crank the setpoint. Point them down in heat mode.
- Heating an empty house. If nobody is home, a timer that pre-warms the room 20-30 minutes before you arrive is far cheaper than holding temperature all day.
Where the savings really come from
- Insulate the ceiling first. BRANZ research puts ceiling losses at 30-35% of total heat loss in an uninsulated home. EECA's Warmer Kiwi Homes grant covers up to 90% of the cost for Community Services Card and SuperGold Combo cardholders, and 50-80% in many other cases.
- Block draughts. Door seals, sash window strips, chimney balloons. Cheap, fast payback.
- Curtains floor-to-ceiling, lined. Halves the heat loss through windows overnight.
Tweaking your heat pump settings is a small lever. Building shell improvements are a much bigger one.
Want to see what your specific setup costs? Plug your heat pump's heat output and your typical hours into the NZ Power Bill Calculator. The "Heat pump vs plug-in heater" panel will also show what you are saving over a column heater doing the same job.
Related guides
- How much does a heat pump cost to run in NZ? - the full cost breakdown by region
- Insulation or a heat pump: where to spend first - building shell improvements reduce the hours you need to run the heat pump
- Heat pump vs wood burner: which is cheaper in NZ? - the per-kWh comparison
- Heat pump running cost calculator - set your own output, COP and hours