Why does my power bill go up so much in winter?

Because heating switches on. BRANZ research puts space heating at about a third of a typical NZ home's energy use, and almost all of it lands in the cold months, so a bill that sat at one level through summer can double through July. Hot water - close to another third - also works harder in winter because the incoming mains water is colder.

What saves the most on a NZ winter power bill?

In order: use an efficient heat source and set it sensibly, stop heat escaping through a leaky building shell, then trim hot water and the always-on loads. A heat pump set no higher than 20-21C in a well-curtained, draught-stopped room is the single biggest lever - it beats chasing small standby savings many times over.

Should I leave the heat pump on all day in winter?

For a well-insulated home you are in most of the day, holding a steady temperature in the 18-21C band is often cheaper and more comfortable than repeatedly heating from cold. For a leaky home, or one empty during the day, heating only the rooms you use when you use them is usually cheaper. Either way, a timer that warms the room just before you need it avoids waste.

Field Note

The NZ winter power-saving checklist

Published 27 July 2026· 7 min read

Winter is where a New Zealand power bill goes to balloon. Through the warm months the number sits still; then the heating comes on and it can double, because space heating alone is about a third of a home's energy use and almost all of it falls in a few cold months. The good news is that winter savings are concentrated in a handful of high-leverage moves. This is the checklist, ordered by what actually saves the most - not by what is easiest to tick off.

1. Fix the heat source first

Nothing else on this list matters as much as how you make heat. A heat pump delivers three to four units of heat per unit of power; a plug-in fan or oil heater delivers one. If you are heating with resistive heaters, moving to a heat pump for the main living space is the biggest single saving available - often cutting the heating portion of the bill by well over half.

Set it to at least 18°C, and no more than 20-21°C. That is EECA's advice: 18°C is also the World Health Organisation's minimum for a healthy home - higher for babies, older people and anyone with a chronic illness - while 20-21°C is the ceiling beyond which you are just burning money. As a rule of thumb each extra degree adds roughly 5-10% to running cost, so the gap between 20°C and 25°C is enormous. The full case is in how warm to set your heat pump.
Let it hold a steady temperature rather than blasting from cold and switching off. Heat pumps are most efficient ticking over gently.
Clean the filters. A clogged filter makes the unit work harder for less heat.
Heat the rooms you use, not the whole house, and close doors to contain the warmth.

2. Stop the heat escaping

Every unit of heat you make leaks straight back out through a cold, draughty shell - so the second-biggest lever is keeping it in. This is often better value than the heater itself: as we argue in insulation or a heat pump, where to spend first, a well-sealed home needs less heat in the first place.

Close curtains before dark, ideally heavy or thermal ones, to trap heat against the cold glass.
Draught-stop around doors, windows and the older joinery - a leaky home is essentially heating the outdoors.
Top up ceiling and underfloor insulation if it is thin or missing; it is the highest-return upgrade most homes can make.

3. Trim the hot water

Hot water is a quarter to a third of the bill year-round, and it works harder in winter because the incoming mains water is colder. A few no-cost tweaks:

Store at 60°C, deliver at 50°C. The cylinder must sit at 60°C or above to keep Legionella at bay, while a tempering valve drops the water at the tap to a safe 50°C. Do not turn the cylinder itself down to save power - that is a health risk, not a saving.
Fix a dripping hot tap. A steady hot drip quietly reheats water all day and is a classic cause of a sudden bill jump.
Shorter showers, and if you are replacing a cylinder, look at a hot water heat pump, which uses a fraction of the power.

4. Round up the sneaky loads

Once the big three are handled, a cluster of small, always-on loads is worth a sweep - individually minor, together a real slice of the bill.

Put the heated towel rail on a timer. Left on 24/7 it costs $200-300 a year at 2026 rates; a $25 timer running it a few hours a day cuts that to well under $50.
Reconsider the second fridge. A garage fridge half-empty of drinks can cost $100 or more a year - switch it off outside party season.
Tackle standby. Idle electronics can be 5-10% of the bill, or around $200 a year; a switchable board kills a cluster at once.

5. Deal with the damp without over-heating

Winter damp tempts people into running heaters and dryers hard. Often a dehumidifier is the cheaper tool - our dehumidifier vs heat pump guide covers when each wins. And for laundry, drying on a rack in a dehumidified room, or using a heat pump dryer, avoids both the running cost and the wall of moisture a vented dryer dumps into the house.

6. Check you are on the right plan

Finally, make sure you are not overpaying for every one of those units in the first place. Confirm you are on the right low-user or standard tariff, see whether a time-of-use plan suits your household, and if it has been a while, switch retailer - it is free and takes minutes.

Put a number on your winter

The fastest way to see which of these matters most for your home is to model it. Open the power bill calculator, set your region, and switch on the appliances you actually run - then watch what happens as you drop the heat pump a degree or put the towel rail on a timer. The winter savings are usually hiding in one or two lines.