What is COP? Understanding Heat Pump Efficiency

A heat pump doesn't make heat, it moves it - pulling warmth from the air into your water. The actual COP - or efficiency performance - depends on your climate and the season.

• COP = how much heat you get out for each unit of electricity in.
• A COP of 3 means the heat pump delivers about 3 units of heat to the water for every 1 unit of electricity it consumes. But COP isn’t a fixed number, it changes with air temperature, water temperature and the conditions used to test the product.
• A standard electric resistance cylinder has a COP of 1 because it converts roughly 1 kWh of electricity into 1kWh of heat.
• A good hot water heat pump has a COP of 3 or more; better products reach 4+.

Not yet. Hot water heat pumps are not regulated for energy efficiency in Aotearoa, New Zealand. There is no mandatory minimum COP, testing standard or label.

A trans-Tasman process is underway: a joint EECA/DCCEEW* consultation closed on 31 October 2025; Australia has since agreed to introduce MEPS (Minimum Energy Performance Standard) and labeling. The New Zealand Government is yet to confirm whether it will follow.

*Australian Department of Climate Change, Energy, the Environment and Water

Don’t compare COP numbers in isolation. Before deciding that one hot water heat pump is more efficient than another, check the conditions behind the number.

Check 1: Air temperature:

What outdoor temperature was used for the test?

Check 2: Water temperature:

What was the incoming water temperature and what temperature was the water heated to?

Check 3: Test standard

Was the COP measured under a recognised standard?

Check 4: Spot or seasonal COP

Is it a single test-point COP or an annual/seasonal performance figure?

Check 5: Who tested it?

Was it independently tested or manufacturer tested?

Check 6: Are you comparing like with like?

COP figures are comparable if the underlying test conditions are reasonably similar.

Without a MEPS hot water heat pumps sold in New Zealand have COP values reported by manufacturers that aren’t always measured under the same test conditions (temperature outside, as well as water inlet and outlets temperatures).

• Many are tested at 19°C or 20°C - which is warmer than New Zealand conditions - meaning their performance here is likely to be lower.
• Remember COP varies across the seasons - and even at a worst case COP of 2 in winter your hot water heat pump is two times more efficient than your old electric cylinder!
• For the products you are comparing check what air and water temperatures the quoted COP applies to - if these are the same or similar that will give you a useful comparison.