Electric Cylinders and the New Energy Performance Standards in NZ
- New Zealand’s Minimum Energy Performance Standards (MEPS) for electric hot water cylinders now require a standing heat loss no greater than 45 Wh per hour for a 180-litre unit, pushing older resistive cylinders out of compliance.
- Switching from a standard resistive electric cylinder to a modern high-efficiency model can reduce water heating energy use by 20–35%, cutting annual household bills by $150–$350 depending on usage and tariff.
Electric cylinder energy standards at a glance
Why energy standards for electric cylinders are tightening
New Zealand’s Ministry of Business, Innovation and Employment (MBIE) has been progressively tightening the Minimum Energy Performance Standards — commonly abbreviated as MEPS — that govern which electric hot water cylinders can be sold in the country. The most recent revision, which took full effect in mid-2025 and is now being enforced through the 2026 compliance cycle, targets standing heat loss: the energy a cylinder bleeds away simply by sitting idle, keeping water hot against the ambient temperature of the room it sits in.
The trigger for this tightening is straightforward. Water heating accounts for roughly 30% of a typical New Zealand household’s total energy consumption. Electric cylinders — the resistive storage type that has dominated the market for decades — are the least efficient way to deliver that heat. Regulators have concluded that the technology has matured enough, and alternatives are affordable enough, that a higher baseline is now achievable at reasonable cost.
What the current MEPS numbers actually mean
Standing heat loss is measured in watt-hours per hour (Wh/h) and varies by cylinder volume. The 2025-onwards standard sets the following maximum allowable heat loss figures for storage electric cylinders sold into the New Zealand market:
- Up to 100 litres: 35 Wh/h maximum standing loss
- 101–200 litres: 45 Wh/h maximum standing loss
- 201–300 litres: 55 Wh/h maximum standing loss
- Over 300 litres: calculated using the formula 0.16 × V⁰·⁶, where V is volume in litres
These figures are tested under AS/NZS 4692.1, the joint Australian and New Zealand standard for electric water heaters. Manufacturers must submit independently verified test results before a product can carry a compliant energy rating label and be legally sold through plumbing supply channels.
Note: Units already installed before the MEPS revision are not required to be replaced immediately. Compliance is triggered at the point of sale or new installation — not retrospectively. However, if a cylinder fails and a plumber installs a direct like-for-like replacement of a non-compliant model, both the installer and the supplier can be liable under the Energy Efficiency (Energy Using Products) Regulations 2002.
How modern electric cylinders meet the standard
Meeting the tighter heat loss limits requires better insulation rather than a change to the heating element itself. Most compliant cylinders now use 50–75 mm of polyurethane foam insulation around the tank, compared with the 35–50 mm that was standard on older models. The tank jacket itself is also sealed more carefully at the thermostat boss, anode rod port, and pipe connections — all points where thermal bridging (heat escaping through a conductive path rather than through the insulation layer itself) can add measurable loss.
For example: an older 180-litre cylinder with 38 mm of insulation might lose 62 Wh/h at a 45°C temperature differential. A compliant 2025-rated unit of the same volume, with 65 mm of closed-cell foam, will typically measure 38–42 Wh/h — within the 45 Wh/h ceiling and meaningfully reducing the base load the household draws 24 hours a day.
You can check whether a specific model is currently compliant by searching the official product register or asking your supplier for the AS/NZS 4692.1 test certificate. Any reputable distributor selling electric hot water cylinders should be able to produce this documentation on request.
The case for going further: heat pump cylinders
While a high-insulation resistive cylinder meets MEPS, it does not come close to the efficiency possible with a heat pump hot water system. A heat pump cylinder — which extracts ambient heat from surrounding air rather than converting electricity directly into heat — operates at a Coefficient of Performance (COP) between 3.0 and 4.5. That means for every 1 kWh of electricity consumed, the system delivers 3 to 4.5 kWh of heat into the water.
The trade-off is upfront cost and installation requirements. A heat pump unit needs adequate air volume around it (typically at least 10–15 cubic metres of free air space), a condensate drain, and ideally a location where the noise output of 45–52 dB does not cause nuisance. For homes where those conditions are met, the payback period against a standard resistive cylinder replacement is currently 4–7 years at average New Zealand electricity prices.
What to do next
- Check the manufacturing date and insulation rating of your current electric cylinder — any unit more than 10–12 years old is likely operating below current MEPS and costing more to run than it needs to.
- Ask your plumber or supplier for the AS/NZS 4692.1 test certificate before any replacement purchase — this is the fastest way to confirm a unit is legally compliant for sale in New Zealand.
- Get a site assessment for a heat pump hot water system if your laundry, garage, or utility room has adequate air volume.
- If a heat pump is not viable for your site, specify a minimum 65 mm polyurethane insulation cylinder and confirm the thermostat is set to 60°C — the minimum safe temperature to prevent Legionella bacteria growth in the stored water.
- Register your new installation with your lines company to check whether a controlled load (off-peak) tariff applies — many households with compliant cylinders can shift the heating load to overnight rates and reduce annual running costs by a further $80–$150.
