What is COP? A Guide to Comparing Efficiency
COP is a number that tells you how efficient a hot water heat pump is.
By Carolyn Cox · Sustainability Expert, 25+ years · Updated August 2026
What the COP?
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 roughly $3 of hot water per $1 of power - 300% efficiency.
- A standard electric cylinder has a COP of 1 - 100% efficiency.
- A good hot water heat pump has a COP of 3 or more; better products reach 4+.
Good COP vs. Bad COP?
Efficiency increases in warmer air and falls in the cold. Meaning a products COP is always higher in warmer climates and lower in colder.
Makers quote COP at a single temperature point - usually 19°C air with a 45°C water-temperature rise.
- Auckland (about 15.2°C on average) sits close to that;
- Central Otago (about 9.6°C, and near 3°C in winter) does not.
- The colder your region, the lower the COP resulting.
When deciding which heat pump to purchase check the COP test conditions to make sure they are comparable.
It’s important to remember that the COP of hot water heat pumps is much higher than traditional electric cylinders even in cold climates.
Is there a minimum standard? MEPS in New Zealand
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
Goes Electric's approach to COP
Goes Electric supports the adoption of a MEPS which will enable more accurate product comparison and informed decision making by homeowners. We’ll update you as soon as any decision is announced.
Our approach:
- The COP (coefficient of performance) currently listed in Goes Electric hot water product specifications is a self-reported number obtained from data published by product brand owners and distributors.
- Currently a variety of test conditions and methods are used which makes product comparison difficult - but not impossible.
- Until a NZ MEPS is in place - to enable better product comparability - we always include details of the test conditions, the standard applied and the name of the tester if they are available - and actively request these when they’re not provided.
How to compare COP claims fairly
- Check what air and water temperatures the quoted COP applies to.
- Match it to your region and compare products on the same conditions.
- Remember COP varies across the seasons - and even at a COP of 2 in winter your hot water heat pump is 200% more efficient than your old electric cylinder!
Australian/New Zealand Standards
- Spot COP - Tested at fixed lab conditions under AS/NZS 5125.1.More commonly used.
- Seasonal COP - An annual average that includes standby losses, calculated under AS/NZS 4234:2021. Less commonly used.
Resources
More information on MEPS and standards:
- EECA: Heat pump water heaters: regulations under review (current MEPS status)
- EECA: Consultation Regulation Impact Statement (CRIS), Oct 2025 [PDF]
- EECA: Decision Regulation Impact Statement (DRIS), Apr 2026 [PDF]
- Standards New Zealand: AS/NZS 5125.1:2014 (COP performance test)
- Standards New Zealand: AS/NZS 4234:2021 (annual energy / seasonal COP)
- Energy Rating (Australia): products under review
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