What Is a Mains Pressure Hot Water Cylinder?
A mains pressure hot water cylinder is connected directly to the street water supply without using a header tank or gravity feed. This means hot water is delivered at the same pressure as your cold water -- full mains pressure at every tap, shower, and appliance in your home.
Unlike low pressure systems that rely on a tank in the roof cavity to create water pressure through gravity, a mains pressure cylinder is a sealed, pressurised vessel designed to handle the full force of the incoming water supply.
In practical terms, you get strong, consistent water flow throughout your home. There is no pressure drop when someone turns on a tap in another room, and your hot water matches the cold water pressure at every outlet. For most modern Auckland homes, mains pressure is the standard and expected setup.
Benefits of Mains Pressure
- Strong showers -- powerful flow without needing a pump
- Modern mixer taps -- required for contemporary fixtures
- Consistent pressure -- hot and cold at the same pressure
- Multi-bathroom homes -- multiple showers run simultaneously
- No header tank -- frees up roof space, fewer leak risks
Rheem mains pressure electric cylinder installed by Water & Gas Worx in Flat Bush, Auckland
How Mains Pressure Cylinders Work
A mains pressure cylinder is built to withstand the full pressure of the incoming water supply, typically between 350 kPa and 600 kPa in Auckland depending on your area. Because the cylinder is under constant pressure, several safety devices are required by New Zealand plumbing regulations:
- Pressure Reducing Valve (PRV) -- installed on the incoming supply to regulate pressure to a safe level for the cylinder, usually around 500 kPa.
- Temperature and Pressure Relief Valve (TPR) -- a critical safety device that releases water if the temperature or pressure inside the cylinder exceeds safe limits.
- Expansion vessel -- may be required to absorb the expansion of water as it heats up, preventing excess pressure buildup in the system.
Electric vs Gas Mains Pressure Cylinders
Electric mains pressure cylinders are the most common type in New Zealand homes. They use one or two electric elements to heat water stored inside the cylinder. Running costs can be reduced by using a night rate or off-peak electricity tariff to heat water overnight.
Gas mains pressure cylinders use a gas burner beneath the cylinder to heat the water. They typically have a faster recovery rate than electric models, meaning the cylinder reheats more quickly after heavy use. Gas cylinders are available in both natural gas and LPG configurations.
Popular Sizes -- Choosing the Right Cylinder
Selecting the right cylinder size depends on your household size and hot water usage patterns:
- 135 litres -- suitable for 1-2 people. Compact and efficient for apartments, units, or small households.
- 180 litres -- a good fit for 2-3 people. The most common size for couples and small families.
- 250 litres -- designed for families of 3-4 people. Handles multiple showers and general household demand comfortably.
- 300 litres -- recommended for larger families of 4 or more, or homes with high hot water usage such as spa baths or multiple bathrooms.
Brands We Install
We supply and install mains pressure cylinders from New Zealand's most trusted manufacturers:
- Rheem -- one of the most recognised names in hot water, with a wide range of mains pressure cylinders in various sizes and configurations.
- Rinnai -- known for build quality and energy efficiency, Rinnai cylinders are a popular choice across Auckland.
- HJ Cooper -- a New Zealand-made brand with a long history of reliable, heavy-duty cylinders built for local conditions.
- Dux -- offering good value with solid warranties, Dux cylinders are a practical option for budget-conscious homeowners.
Upgrading from Low Pressure to Mains Pressure
Many older Auckland homes still have low pressure hot water systems with a header tank in the roof. Upgrading to mains pressure is one of the most worthwhile improvements you can make. Here is what is typically involved:
- New cylinder -- the existing low pressure cylinder must be replaced with a mains pressure rated unit.
- PRV installation -- a pressure reducing valve is fitted on the incoming supply to protect the new cylinder.
- Pipe assessment -- older homes may have smaller diameter pipes (15mm) that restrict flow. In some cases, upgrading to 20mm pipe runs to bathrooms and the kitchen is recommended to get the full benefit of mains pressure.
- Tapware compatibility -- some older taps and valves were designed for low pressure only. These may need to be replaced to handle the higher pressure safely.
- Header tank removal -- the old roof-mounted header tank and associated pipework can be removed, freeing up space in the ceiling.
Mains Pressure in Auckland
Newer Auckland homes built after 2000 are almost universally fitted with mains pressure hot water systems. Suburbs with significant new housing development -- including Botany, Flat Bush, Albany, Hobsonville, and Long Bay -- are predominantly mains pressure. Watercare supply pressure does vary by area and elevation, which is why a correctly sized PRV is essential for every installation.
If you are in an older suburb and still running a low pressure system, an upgrade to mains pressure will transform your daily experience. The difference in shower quality alone makes it worthwhile.
Comparing Your Options?
If your home currently has a low pressure system and you are weighing up your choices, see our low pressure hot water cylinder page for a detailed comparison.
Frequently Asked Questions
How much does a mains pressure hot water cylinder cost in Auckland?
The Rheem Mains Pressure 180L is $3,499 incl GST fully installed. Supply only is $1,299. If you are upgrading from low pressure, the cost is higher because additional valves, pipework, and fittings are required. We provide a fixed quote before any work starts so there are no surprises.
How long does it take to replace a hot water cylinder?
A straight like-for-like mains pressure cylinder replacement is usually completed in 3 to 4 hours. If you are upgrading from a low pressure system, allow 4 to 6 hours as the additional valves and pipework take longer to install. Either way, you will have hot water by the end of the day.
How long does a mains pressure hot water cylinder last?
Most mains pressure cylinders last between 15 and 25 years depending on the brand, water quality in your area, and whether the anode has been maintained. If your cylinder is over 15 years old and showing signs of rust, leaking, or inconsistent temperature, it is worth getting it checked.
Can I upgrade from low pressure to mains pressure?
Yes. This is one of the most common upgrades we do across Auckland, especially in older suburbs like Grey Lynn, Mt Eden, Ponsonby, and Devonport. The upgrade involves replacing the cylinder, installing a pressure reducing valve, and removing the old header tank. Some older pipes and tapware may also need upgrading to handle the higher pressure safely.
What size hot water cylinder do I need?
As a general guide: 135L for 1-2 people, 180L for 2-3 people, 250L for 3-4 people, and 300L for larger families or homes with multiple bathrooms. We will recommend the right size based on your household and usage patterns.
Is mains pressure better than low pressure?
For most people, yes. Mains pressure gives you strong, consistent hot water at every tap and shower. It works properly with modern mixer taps and thermostatic shower valves. The only downside is that mains pressure systems have more components (PRV, TPR valve, expansion vessel) that need occasional maintenance.
