Heat Pump Hot Water

Mains Pressure vs Low Pressure Cylinders

Nowadays, New Zealand installations mainly opt for unvented cylinders operating at mains pressure. Such a setup ensures that hot water is supplied at the same pressure as the mains, resulting in shower and tap performance that is consistent and of the expected standard.

On the other hand, erstwhile low pressure systems which are typical of aged residential quarters use gravity feed from a header tank and, therefore, cannot be expected to provide a flow that is as strong as you are used to nowadays.

What to Consider When Choosing a Size

Choosing the right cylinder isn’t just about litres — it’s also about how you live:

1. Household Size & Demand

The number of occupants and their habits (e.g., long showers, multiple bathrooms) play the biggest role in sizing decisions. 

2. Peak Usage Times

Think about busiest times — morning routines, evening baths, or frequent laundry — to ensure the cylinder can cope with simultaneous hot water draws. 

3. Physical Space

Cylinders take up room. Typical diameters range from roughly 460 mm to 810 mm, with most around 480–580 mm, so measure your installation area before buying.

4. Heating Source & Future Upgrades

If you plan to switch to solar or heat pump water heating later, some cylinders are easier to adapt than others. Certain Rinnai models, for example, offer compatibility with solar and heat pump connections. 

5. Standing Heat Loss

Short, broad cylinders tend to have lower heat loss compared to tall, slim models — meaning better energy efficiency over time. 

What You Need to Know — Impact on New Installations & Replacements

If you are installing a new hot water cylinder — or replacing an existing system — here are the key implications of the regulation change:

• A tempering valve (or thermostatic mixing valve) is now required in any new installation or replacement to reduce water temperature at points of use (taps, showers) to no more than 50 °C.
• Stored water temperature remains at 60 °C — cylinder thermostats and heating elements must ensure water is hot enough for safe storage and bacterial control.
• “Low-to-low” (low-pressure) systems are also affected — even older, simpler systems require a tempering valve if replaced under the new rules.
• Changes apply only for new or replaced systems — existing cylinders already installed before 1 Nov 2024 are not automatically required to be upgraded, though retrofitting a tempering valve is advisable for safety. In essence: the update increases safety standards for hot water delivery, particularly in homes with vulnerable users — something all homeowners should take seriously.

Why These Changes Are Important — Safety, Compliance & Peace of Mind

The lowered tap-water temperature limit helps prevent scald injuries — a real risk, especially in multi-generational households, with children or older residents. Reducing the risk of burns while maintaining sufficient stored hot-water temperature strikes a balance between safety and hygiene.

At the same time, compliance with the updated building code ensures your hot water system meets current standards — an important consideration if you sell your home, make renovations, or need compliance documentation.

Additionally, the requirement for tempering valves means that water delivered to taps is safer, while still preserving stored water at hygienic levels (≥ 60 °C). It’s a simple but highly effective safety upgrade.

Why a Heat Pump Water Heater Is Often the Better Choice

Switching to a heat pump-powered hot water cylinder (HWHP) delivers a number of advantages over gas — often for lower ongoing cost and greater convenience:

• Lower​‍​‌‍​‍‌​‍​‌‍​‍‌ operating costs: Heat pumps rely on ambient air to heat water, thus using very little energy as compared to gas or electric resistance heating. A large number of users report that energy bills significantly drop when they switch to heat pumps from gas water heaters.
• Reliability and consistent performance: Up-to-date heat pump units (in particular CO₂-based ones) are designed in such a way that they can operate efficiently even in cold climates — thus a permanent hot water supply can be guaranteed throughout the year.
• Large volume of hot water for households: Heat pumps have the ability to provide high volumes of hot water per day — this is sufficient for a busy household with many members or a high hot water demand.
• Environmental advantages: Heat pumps (especially when powered by natural refrigerants such as CO₂ or R290) have less than half the greenhouse-gas emissions of gas systems — a considerable advantage for those households that want to lower their carbon footprint.
• No gas bottles, no delivery inconveniences: In case of LPG users, the decision to switch to a heat pump means that they are free from the trouble of keeping an eye on gas bottles, scheduling replacements, or managing deliveries — a great deal of convenience is ​‍​‌‍​‍‌​‍​‌‍​‍‌gained.

Key Criteria to Evaluate in a Hot Water Installer

Credentials and Compliance

Make​‍​‌‍​‍‌​‍​‌‍​‍‌ sure that your installer holds a license and is aware of local building regulations as well as safety standards that are very much applicable in the case of gas or mains-pressure systems where proper ventilation, flues, and safety valves need to be complied ​‍​‌‍​‍‌​‍​‌‍​‍‌with.

Experience with Different Systems

Whatever​‍​‌‍​‍‌​‍​‌‍​‍‌ method you decide for your water heating – solar, gas, electric, or heat-pump, – make sure the installer you choose is a person who can demonstrate that he/she has experience specifically with that kind of system. A general plumber might not be able to give you the best outcome for your highly specialised ​‍​‌‍​‍‌​‍​‌‍​‍‌systems.

Proper Assessment & Correct Sizing

The​‍​‌‍​‍‌​‍​‌‍​‍‌ installer who is really good will go through the evaluation of how much hot water your family consumes, the number of people living in the house, and the bathing/laundry needs, and as a result, they will be able to recommend the right size and the right configuration of the cylinder that will work for you — thus, making sure that you will not have a system that is either under- or ​‍​‌‍​‍‌​‍​‌‍​‍‌oversized.

Safe Installation & Quality Workmanship

Correctly-installed​‍​‌‍​‍‌​‍​‌‍​‍‌ piping, valves, and insulation should be a part of the installation, and, if necessary, a ventilation or a flue should be added. Also, pressure-relief valves, thermostats, and anode rods should be tested and mounted in accordance with the manufacturer’s ​‍​‌‍​‍‌​‍​‌‍​‍‌instructions.

Warranty, After-Service and Maintenance Support

A​‍​‌‍​‍‌​‍​‌‍​‍‌ dependable installer will promise the quality of their work, be available for after-service support, and give you the regular maintenance instructions (such as flushing tanks, checking valves, or replacing anode rods) in order to keep your hot water system in good condition for a long ​‍​‌‍​‍‌​‍​‌‍​‍‌time.

When Repair Might Work — and When Replacement Is Necessary

Not all cylinder issues require a full replacement. If the problem is isolated to a single component, such as:

• A faulty thermostat
• A broken heating element
• A worn-out valve

…then a repair can restore the system to good working order.

However, if problems are recurrent, systemic, or due to corrosion, leaks, or sediment buildup, or if the cylinder is older than 10 years, replacement is often the safer and more cost-effective solution. Investing in a new cylinder avoids ongoing maintenance costs, reduces the risk of emergencies, and provides peace of mind.

Replacing for Better Efficiency and Performance

Modern hot water cylinders offer significant advantages over older models, including:

• Improved insulation for less heat loss
• Faster recovery times so hot water is available sooner
• Compatibility with solar or heat pump systems for eco-friendly and energy-efficient solutions

Upgrading your cylinder can lead to consistent hot water supply, lower energy bills, and safer operation. Choosing the right size and system type is key, and professional advice ensures the replacement suits your household needs perfectly.

Types of Hot Water Cylinders in New Zealand

Understanding the different types of cylinders available helps you choose the right system for your home:

• Direct Electric Cylinders – Heat water using internal immersion elements. Ideal for homes without a central heating system or external boiler.
• Indirect Cylinders – Use a coil connected to an external heat source such as a gas boiler, solar water heater, or heat pump. Energy-efficient and effective for households with central heating or solar systems.
• Vented vs. Unvented Cylinders – Vented cylinders rely on gravity and are usually low-pressure systems, while unvented (mains pressure) cylinders provide strong flow to multiple outlets.

Choosing the right cylinder depends on your household’s water usage, number of bathrooms, and available heating sources.

Key Components of a Hot Water Cylinder

A quality cylinder has several components that ensure safe, efficient operation:

• Inner tank – Holds the water and is usually lined to resist corrosion.
• Heating element or coil – Directly heats water or transfers heat from an external source.
• Thermostat – Maintains the desired temperature automatically.
• Temperature-Pressure Relief (TPR) Valve – Safety device to prevent over-pressurisation or overheating.
• Insulation – Reduces heat loss, keeping water hot longer.
• Cold water inlet and hot water outlet – Designed to maximise efficiency and water flow.
• Drain valve / maintenance access – Allows flushing and servicing to remove sediment and maintain performance.

Why Heat Pumps Are Gaining Popularity in NZ Homes

Here are the main advantages that make heat‑pump hot water systems attractive for New Zealand households today:

Energy Efficiency & Lower Power Bills – Because heat pumps move existing heat rather than generating it from electricity or gas, they use significantly less energy. Compared with standard electric resistance cylinders, they can use around 60‑75% less electricity for water heating. Over time, this translates into real savings on electricity bills — especially for larger households or homes with high hot‑water demand.

Reduced Environmental Impact – Heat pumps contribute to lower greenhouse‑gas emissions compared with gas or electric resistance heaters. Since much of New Zealand’s electricity generation is low‑carbon, switching to a heat pump for water heating can significantly reduce your home’s carbon footprint.

Flexibility and Space Savings – Heat‑pump systems can often be installed outdoors, freeing up internal space (like cupboards or small laundry areas). Additionally, for new builds, retrofits, or renovations, heat pumps offer a flexible option, often easier to integrate than bulky tanks or gas‑fired systems.

Aligns with NZ’s Clean‑Energy Goals As New Zealand moves toward cleaner energy, heat‑pump water heaters support national efforts to reduce energy consumption and emissions — making them a future‑proof choice for environmentally conscious homeowners.

Key Benefits for New Zealand Homes

Energy Efficiency & Lower Running Costs

A​‍​‌‍​‍‌​‍​‌‍​‍‌ heat pump usually consumes 60–75% less electricity than regular electric water cylinders, since it moves heat rather than using electric resistance or combustion.

As a result, this means for a lot of homes, in particular, those with a hot water demand that is above average (families, several bathrooms, daily showers), substantial savings on electricity bills can be made over ​‍​‌‍​‍‌​‍​‌‍​‍‌time.

Environmentally Friendly & Lower Emissions

Electrically​‍​‌‍​‍‌​‍​‌‍​‍‌ powered hot water heat pumps do not burn fossil fuels – this implies that they emit significantly fewer greenhouse gases than gas or LPG water heaters.

As a result of New Zealand’s predominantly renewable electricity grid, the utilization of a heat pump is a good way to achieve a cleaner and greener ​‍​‌‍​‍‌​‍​‌‍​‍‌household.

Flexibility & Installation Advantages

• Many heat pump units are designed so that the outdoor “pump/compressor” can sit outside the house, while the water cylinder can be indoors — saving internal cupboard or storage space.
• This flexibility makes them suitable for a broad range of housing types: standalone homes, townhouses, or smaller dwellings.

Long‑Term Value & Energy Efficiency Over Time

Though the upfront cost of a heat‑pump system is higher than a basic electric cylinder, the long-term savings — in both energy costs and carbon footprint — often make them the most cost-effective choice over the life of the system.

Common Hot‑Water Issues at Holiday Homes — And How to Diagnose Them

When you return to your holiday home and find hot water isn’t working as expected, these are the usual culprits — and what to check first:

 Power or Supply Problems

• Ensure the hot water system has power: check if a circuit breaker has tripped or a switch is off. Electric cylinders are often switched off when homes are left vacant — and not always remembered when you return.
• If using a gas system: the pilot light or ignition may need re‑lighting. Gas heaters can lose their pilot flame over time or due to drafts — a common oversight after long periods of non‑use.

Sediment Buildup & Tank Efficiency Issues

Mineral deposits and sediments settle at the bottom of a cylinder over time — especially if water is left standing unused. This buildup can reduce heating efficiency, cause strange noises, or shorten the supply of hot water. Flushing the tank helps restore performance.

Faulty or Stuck Safety/Pressure Valves

A malfunctioning pressure‑relief (or temperature‑pressure relief) valve can trigger leaks, block heating, or prevent normal operation. When a cylinder has been idle, valves can seize or corrode. Testing or replacing faulty valves is often a necessary first step.

Heating Element & Thermostat Failures (For Electric Cylinders)

If you get cold water or inconsistent temperature, the immersion heater (or booster) or thermostat may have failed or “tripped out” during the downtime. This is common — especially after long vacancy.

Corrosion, Leaks or Pipe Damage — Especially with Age or Neglect

Cylinders that are older, unused, or poorly maintained are at risk of corrosion, leaking around fittings, or weakened tank bodies. Small drips or rust stains at the base can indicate bigger internal issues — which pose risk of flooding or catastrophic failure.

Easy Checks & Basic Fixes — What You Can Do Before Calling a Plumber

If your holiday home’s hot water isn’t working, here’s a quick checklist to walk through. Many issues can be fixed before resorting to professional help:

1. Check power or gas supply — Ensure circuit breakers are ON, switches flipped, or gas/isolation valves open. If gas: try relighting the pilot light following manufacturer’s instructions.
2. Inspect for leaks or drips — Look around the base, valves, and pipe connections for water or rust stains. Even small leaks could signal pressure-valve or tank issues.
3. Test the temperature‑pressure (T/P) / relief valve — Operate the test lever gently to check flow, then see if it reseals properly. If stuck or leaking, replacement may be needed.
4. Flush the cylinder — Especially if the unit hasn’t been used in many months: drain part of the tank, flush out sediment, then refill — this often restores heating efficiency and prolongs the tank life.
5. Check the heating element / thermostat — In electric systems, a tripped thermostat or faulty heater element might be the culprit. If you suspect this, switch off power and water before any further inspection.
6. Restore startup sequence — For gas heaters remember to re‑open gas valves and re‑light the pilot; for electric, ensure supply and switches are enabled. Then allow enough time for the tank to reheat (especially if water inside has cooled significantly).

If after these steps hot water still fails or you spot corrosion/leaks: call in a professional to avoid risking damage or safety issues.