What the November 2024 Building Code Update Means for Your Hot Water System
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Understanding the Recent Changes to NZ Plumbing & Hot Water Regulations
As of 1 November 2024, New Zealand’s Building Code update for acceptable solution G12/AS1 came into effect, introducing a major shift in how domestic hot water systems are installed.
The biggest change? The maximum allowable water temperature delivered to personal hygiene taps—your showers, baths, and bathroom vanities—dropped from 55°C down to 50°C.
Here is a straightforward breakdown of what changed, why it matters, and how it impacts your home if you’re replacing or upgrading a hot water cylinder.
The Core Rule: 60°C in the Tank, 50°C at the Tap
The updated code balances two critical safety priorities: scald prevention and bacterial control.
At the Tap (Max 50°C): Water over 55°C can cause serious third-degree burns to a young child or elderly person in less than five seconds. Lowering the tap limit to 50°C provides a crucial buffer, giving you much more reaction time to prevent severe scalding injuries.
In the Tank (Min 60°C): While tap water is now cooler, your cylinder must still store water at a minimum of 60°C. Keeping stored water hot is non-negotiable—it kills off Legionella bacteria and keeps your water supply safe to drink.
To bridge this gap, every new installation or cylinder replacement now requires a tempering valve (or thermostatic mixing valve) fitted to the system. The valve blends cold water into the hot supply line as it leaves the cylinder, dropping the temperature sent to the bathroom down to 50°C while keeping the tank safely at 60°C.
Does This Apply to Your Home?
Whether you need to take action right now depends on what you’re doing with your hot water setup:
1. Replacing an Existing Cylinder (Or Building New)
If your cylinder dies and you install a replacement—or if you’re doing a major renovation/new build—your installation must comply with the 50°C limit. Your plumber will fit a compliant tempering valve as part of the job.
2. Upgrading an Older Low-Pressure System
This rule isn’t just for high-pressure stainless steel cylinders. If you are replacing an older copper low-pressure cylinder with a like-for-like low-pressure unit, it still requires a tempering valve under the new rules.
3. Existing Systems (No Changes Planned)
If your hot water cylinder was installed before November 2024 and is running fine, you aren’t legally forced to retrofit a valve today. However, if you have young kids or elderly family members in the house, retrofitting a tempering valve onto your current cylinder is a safety upgrade that a plumber can do.
Key Things to Keep in Mind
Kitchen Sinks are Handled Differently: The 50°C limit applies strictly to sanitary fixtures used for personal hygiene (bathrooms and ensuite basins/showers). Kitchen sinks and laundries can still receive hotter water if needed for dishwashing or cleaning, though many modern installations temper the whole house for simplicity.
Consents & Compliance: When you sell your home or make an insurance claim, unpermitted or non-compliant plumbing work can cause serious headaches. Ensuring your new cylinder setup has a properly calibrated tempering valve protects your home’s compliance status.
Get the Thermostat Set Right: Never try to meet the 50°C tap rule by simply turning down your cylinder’s thermostat. Doing so puts your home at risk for Legionella growth. The thermostat stays at 60°C (or higher), and the tempering valve does the work of cooling the water down before it reaches your hands.
How We Handle Your Installation
When our team replaces or installs a hot water cylinder, we ensure the setup is fully compliant with the updated G12/AS1 standard:
We fit a high-flow, compliant tempering valve matched to your system (whether low pressure or mains pressure).
We calibrate your cylinder thermostat to maintain a safe 60°C+ storage temperature.
Adjusting the tempering valve so your showers run at a safe, comfortable 50°C without risking scalds.
If your cylinder is getting on in years or you’re planning an upgrade, get in touch with The Cylinder Guy team on 0800 234 800. We’ll make sure your hot water is safe, efficient, and 100% compliant with NZ code.