Heating water accounts for a significant chunk of the average New Zealand household's energy bill. If your hot water cylinder and pipes are uninsulated, you could be paying to heat water that then loses that heat before it even reaches your tap. The good news is that insulating both is a relatively straightforward and cost-effective upgrade — and in some cases, it's a legal requirement for rental properties.
Why Insulating Your Hot Water Cylinder Matters
A hot water cylinder works by heating water and keeping it hot until you need it. If the cylinder itself isn't well insulated, it loses heat to the surrounding air continuously — this is called standby heat loss. Older cylinders, particularly the bare copper or lightly wrapped models common in New Zealand homes built before the 1990s, can lose a surprising amount of heat overnight.
Modern cylinders usually come with factory-fitted insulation, but older units can benefit enormously from an aftermarket cylinder wrap (sometimes called a cylinder jacket or blanket). According to BRANZ, reducing standby heat loss is one of the most cost-effective energy-saving measures available to NZ homeowners.
Healthy Homes Standards and Rental Properties
If you're a landlord, this isn't just about saving money — it's the law. The Tenancy Services Healthy Homes Standards require that hot water cylinders in rental properties meet minimum insulation requirements. Cylinders must have the manufacturer's insulation or a wrap that meets a specified R-value, and all accessible hot water pipes must be insulated. Make sure you check the current requirements on the Tenancy Services website, as deadlines and specifics can be updated.
Insulating Your Hot Water Cylinder: What's Involved
For most older cylinders, you can purchase a pre-cut cylinder wrap from hardware stores like Bunnings or Mitre 10. These are typically made from fibreglass or polyester and are designed to fit standard cylinder sizes.
What to check before you start
- Cylinder type: Electric storage cylinders are generally safe to wrap. Gas califont (continuous flow) units are different — do not wrap these, as they need ventilation.
- Condition: If your cylinder is old, corroded, or showing signs of leaking, get it assessed by a plumber before adding insulation.
- Thermostat access: Make sure the wrap doesn't block the thermostat or pressure relief valve.
- R-value: Aim for a wrap that provides a meaningful improvement in thermal resistance. Check product specifications at your hardware store.
Installation steps (electric storage cylinders)
- Turn off the power to the cylinder at the switchboard.
- Wrap the cylinder jacket around the unit, following the manufacturer's instructions.
- Secure it neatly without covering the pressure relief valve outlet pipe, thermostat, or any fittings.
- Turn the power back on.
This is a job most capable DIYers can handle safely, but if you're unsure, a plumber or insulation installer can do it quickly.
Insulating Hot Water Pipes
Pipe insulation (also called lagging) reduces heat loss as hot water travels from the cylinder to your taps. It also helps prevent cold-water pipes from sweating in humid conditions and offers some protection against freezing in colder South Island or high-altitude locations.
Foam pipe lagging is inexpensive and widely available. It comes in various diameters — measure your pipe diameter before buying. It's typically split along one side so you can simply press it onto the pipe.
Which pipes to prioritise
- The first metre or two of pipe leaving the hot water cylinder — this is where the most heat loss occurs.
- Any long pipe runs through unheated spaces like under the floor or in the roof cavity.
- Pipes in cold or exposed areas (garages, crawl spaces).
Pipe insulation comparison
| Pipe location | Priority | DIY-friendly? |
|---|---|---|
| First 1–2 m from cylinder | High | Yes |
| Under-floor runs | High | Yes, if accessible |
| Roof cavity runs | Medium | Yes, if safe to access |
| In-wall pipes | Low | Generally not practical |
| Cold water inlet pipe | Low–Medium | Yes |
Cost vs. Savings: Is It Worth It?
As a guide, cylinder wraps and pipe lagging are among the more affordable home insulation products — typically well under a few hundred dollars for materials on a standard setup. The payback period depends on your hot water usage, cylinder age, and energy tariff, but for older uninsulated cylinders the savings can be meaningful over a year. Energywise has useful guidance on energy-saving measures and their relative value for NZ homes.
When to Call a Professional
While wrapping a cylinder and lagging accessible pipes is generally DIY-friendly, there are situations where you should bring in a licensed tradesperson:
- Plumbing connections or pipe repairs — any work on the actual plumbing system (cutting, joining, or modifying pipes) is restricted work under the Plumbers, Gasfitters and Drainlayers Act and must be carried out by a licensed plumber registered with the PGDB.
- Electrical work on the cylinder — adjusting wiring, replacing elements, or any work inside the electrical connections is restricted electrical work and must be done by a registered electrician (see EWRB).
- Gas hot water systems — any work on gas califonts or gas connections must be done by a licensed gasfitter.
- Roof cavity or under-floor access — if you're not comfortable working in confined or elevated spaces, hire a professional insulation installer.
A qualified insulation installer or plumber can assess your whole hot water system and recommend the best approach. You can find local, vetted tradespeople at tradedirectory.co.nz.
Safety Note
Always turn off power to your hot water cylinder at the switchboard before touching it. Hot water systems operate under pressure — never tamper with the pressure relief valve or any plumbing fittings unless you are licensed to do so.