A bar heater turns one unit of electricity into one unit of heat. A heat pump uses one unit of electricity to move heat from outside your house, and you get about three units of heat inside. Same power bill, three times the warmth.
The catch is where that three comes from. It’s measured in a lab at 7°C. That’s a mild spring day in most of the country. Dunedin in July is not a mild spring day. In a real New Zealand winter, with a unit that’s sized and installed properly, you’re looking at more like 2.5 to 3.5. Still miles ahead of any plug-in heater. Just not quite the number on the sticker.
→ Related: How to size a heat pump for your home
Heat pump COP: the number on the label isn’t the number you’ll get
Heat pump efficiency is measured by something called COP, the Coefficient of Performance. A COP of 3 means one kilowatt of electricity gives you three kilowatts of heat.
The testing temperature is the problem. New Zealand heat pumps get rated at an outdoor temperature of 7°C. That’s a fair way to compare one model against another. It’s not what you’ll see in July.
EECA reckons anything at 3 or above is acceptable, and good models sit around 3.5 to 4 on the label. Those are comparison tools, not promises.
| Lab COP (7°C) | Realistic NZ winter | What it means | |
|---|---|---|---|
| Budget model | ~3.2 to 3.8 | ~2.5 to 3.0 | Cheaper upfront, you pay for it on the power bill |
| Mid-range | ~3.8 to 4.5 | ~3.0 to 3.5 | The sensible sweet spot for most homes |
| Premium / cold-climate | ~4.5+ | ~3.5+, holds up below zero | Worth the extra in cold regions |
These are indicative ranges based on typical NZ residential units. Your mileage will vary.
What actually changes heat pump efficiency
How cold it is outside. The bigger the gap between outside and inside, the harder the unit has to work. At 0°C a standard heat pump’s COP might drop to around 2.5. Below -10°C, some units drop to 1.5 or worse. At that point you’re basically running a fancy resistance heater. This matters a lot in Queenstown, Dunedin, and parts of the central North Island. Less so in Auckland.
Whether it’s the right size. Too small and it runs flat out all winter, defrosts constantly, and burns more power than it should. Too big and it short-cycles, blasting on and off, which is also inefficient and wears the unit out faster. Getting this right means someone actually looking at your room, not a calculator on a website.
How well it’s installed. Long pipe runs, too many bends, poor placement, uninsulated lines. Every one of those quietly eats into the efficiency you paid for. Each 90° bend in the refrigerant pipe costs you roughly 1% of capacity. A cheap install can wipe out the advantage of a good unit.
Whether you look after it. A clogged filter or a dirty outdoor coil makes the compressor work harder. Basic cleaning matters more than most people realise.
Defrost cycles. When it’s cold, moisture in the air freezes on the outdoor coil and the unit has to stop heating to defrost itself. Some defrosting is normal. Constant defrosting means the unit is undersized or struggling, and it’s just wasting energy.
→ Related: Heat pump maintenance checklist for NZ winters
Heat pump running costs: what this looks like on your power bill
A 5 kW heat pump heating the living room for 6 hours a day through a Waikato winter. Power at 40c a kWh, about what a Hamilton household pays (MBIE’s August 2026 survey puts the national average at 42.1c). Real-world COP of 3.5.
The heat pump draws about 1.4 kW, so roughly 57c an hour. Call it $3.40 a day, or around $100 a month in the coldest stretch.
A 2.4 kW bar heater running flat out draws the full 2.4 kW. That’s about 96c an hour, or $5.75 a day. Around $170 a month. And that only buys you 2.4 kW of heat, less than half of what the heat pump puts out. To match the heat pump’s warmth you’d need two bar heaters going, at close to $350 a month.
Over a winter, that gap is several hundred dollars. Over the 15-year life of the unit, it’s thousands. Yes, the heat pump costs more upfront. EECA puts a typical installed system around $4,400, and most single-room installs land somewhere between $2,000 for a small bedroom unit and $5,500 for a big open-plan one (see typical NZ installed prices). Either way, it wins comfortably on running costs.
→ Related: Heat pump running costs: real numbers for NZ homes
Cold-climate heat pumps: if you live somewhere properly cold
In Central Otago, Southland, or up on the Central Plateau, a standard heat pump can spend a chunk of winter running below its rated capacity or defrosting constantly. That’s not a fault. It’s physics.
What you want is a cold-climate model that holds its full heating output at low outdoor temperatures. Mitsubishi Electric’s HyperCore range, for example, guarantees full rated heating down to -15°C and keeps running down to -25°C. You’ll pay more for it. In Invercargill, it’s the difference between a heat pump that works and one that just exists.
In Auckland or Tauranga, skip this section entirely.
→ Related: Best heat pumps for cold NZ climates
Three things to ask before you get a heat pump quote
One: ask for the H2 or H3 rating, not just the H1 number. Standardised testing includes lower-temperature ratings at 2°C and colder. A unit that holds its COP at H2 is a better bet for a real NZ winter than one that only looks good at 7°C.
Two: make sure they size it properly. They should be asking about room size, insulation, glazing, and which way the room faces, not just floor area. If someone quotes you over the phone without visiting, that’s a red flag.
Three: ask what happens below zero. A good installer will tell you honestly how the model performs at your local winter lows, and whether a cold-climate unit is worth the premium for your address. If they dodge the question, that tells you something too.
→ Related: Questions to ask a heat pump installer
Are heat pumps worth it in New Zealand?
A heat pump is still the cheapest way to heat a New Zealand home over time. About a quarter the running cost of a bar heater, and cheaper than gas or wood. But the headline “300% efficiency” is a starting point, not a promise. What you’ll actually get depends on where you live, what you buy, and who installs it.
One honest warning. When BRANZ looked at 160 homes with heat pumps, more people said their power bills went up after getting one than said they went down, and only 15% rated the running costs as excellent. The reason is simple: people kept their homes warmer than before. A heat pump makes warmth cheap, so most households use more of it. That’s a win for comfort and health, but if the bill is your main goal, keep the setting around 18 to 21°C and use the timer.
Get those three right and the numbers stack up. Get them wrong and you’ve paid a premium for a machine that behaves like a fancy fan heater.
Want a number for your actual home? Get a quote from an installer who’ll size it properly, not from a calculator.