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Information on products and systems

Electric Hot Water Cylinder vs. Gas Infinity System

When considering an upgrade, replacement or installation, you want to make sure the needs of your family or tenants are met by whatever system you choose. Below we explain and compare the two most common systems - Electric Hot Water Cylinder and the Gas Infinity (continuous) hot water system.

If you are unsure of what to choose, we are just a click away! Live chat, call, txt or email us and fire away with your questions!

Keep in mind we do provide free quotes.

Electric Hot Water Cylinder
  • Does not need gas supply to house

  • Works on low pressure or high/mains pressure water supply

  • Can have wetback or solar addition

  • Commercial/large properties can have this in combination with gas infinity hot water system

  • Water storage capacity can be adjusted for larger properties

  • In the event of a power cut, hot water is still available for a while as cylinder remains warm up to a day

  • Ability to use heat from cylinder for drying clothes or storage of linen etc.

  • ​Large storage space required internally or externally

  • Requires a long time to get cylinder to temperature if hot water is used up or just been switched on

  • More difficult to access for replacement or repair

  • Requires a water catch safe tray

  • Water must be stored at correct temperature or above otherwise risk of Legionnaires disease

  • When they burst, can cause extensive damage if there is no safe tray (commonly missing in most houses)

Gas Infinity Hot Water
  • Never run out of hot water (provided water and gas supply)

  • Externally located frees up cupboard space​

  • Very efficient, only pay for what you use

  • Instant hot water - water is heated instantly and on-demand. (Great for a bach)

  • Some do not require power supply

  • Mains pressure water supply

  • Small storage space required internally or externally

  • Easier to access for replacement or repair

  • Does not require a water catch safe tray

  • Little/no risk of Legionnaires disease

  • Most require power supply - no hot water when there is a power cut

  • May require more maintenance (some never have to service, some should approx. every 3 years) 

  • Requires a gas supply (natural or LPG)

  • More vulnerable to theft when stored externally

  • LPG gas supply requires bottle storage

  • Works most effectively on high pressure

Hot water cylinder. How does a Hot Water Cyliner Work? Hot Wate Cylinder explained NZ. Hot Water Cyliner Plumbing

Untempered hot water feed.

This is only allowed to feed the laundry tub and kitchen sink. This temperature can be 60-70+C.

This is a tempering valve.

This combines with the cold water feed to meet the set temperature on the valve. This will usually supply all the hot water feeds in the house.

This temperature can be set anywhere up to a maximum of 60C. 

In some circumstances the temperature may be lower for places such as childcare centres.

The Electric Hot Water Cylinder System Explained.

The temperature of a hot water

cylinder must be set at a minimum

of 60C. This is because temperatures below this allow the growth of a harmful bacteria which 

cause Legionnaires Disease.

Drain for cylinder incase it ever needs to be emptied

Cold water feed.

This diagram is based on a low pressure system. The mains pressure system will have more valves etc. For more information, click here.

The Heating Element.

This heats and maintains the temperature of the water.

The open vent pipe or valve.

This allows the cylinder to breathe.

It determines the pressure available in the cylinder. Without this, the cylinder could burst.

The electric hot water cylinder is the most common hot water heating system found in New Zealand homes.


Many of the older hot water cylinders do not have the tempering valve that can be seen in the diagram. This means the hot water feed in the plumbing is untempered. This is not up to today's standards.

The electric hot water cylinder shown is heated by an electric element. Alternatively, these can be heated by a gas fuelled burner - this is called a gas hot water cylinder.

There is a thick layer of insulation around the tank (not shown here) which helps maintain the temperature.

Modern hot water cylinders usually have improved insulation and sometimes have multiple elements to heat the water faster.

If you have trouble constantly running out of hot water from water hungry kids or family members, you may want to consider a bigger cylinder or a

gas continuous hot water system.

If you empty all the heated water from the hot water cylinder, there will only be cold water left. This is why your hot shower turns cold. 

The tempering valve will stop 

combining it with the cold water feed, the water supplied will be the current water temperature of the cylinder water.

Electric HWC
Gas Infinity
The Gas Infinity Water Heating System Explained.

House hot water feed.

The temperature of the feed will be set on the system, controller or some systems it can be controlled by an app.

The cold water is heated through these winding coils around the heat exchanger - much like a radiator in your car (but thats for cooling!).


Flow sensor.

This senses the incoming pressure into the system and reduces it to the right pressure.

Flue for combustion of burnt gas

Heat Exchanger

The heat from the burner travels up through heat exchanger. This heats the pipes in turn heating the cold water feed.


The burner is fuelled by the gas feed.

Combustion Fan.

This clears the flue products and sucks clean air in for combustion.

Gas supply.

This can be natural gas (town supply) or LPG bottles.

There is a valve going into the system where you can switch off the gas feed.

Cold water feed

The Gas infinity hot water system is an increasingly popular choice.

This can run on either natural gas (town supply) or LPG bottles. 

The gas infinity hot water system is very efficient as you only pay for what you use. The water is heated instantly on demand, in comparison with a HWC (hot water cylinder) which heats when required to maintain or bring new water up to temperature. 

This system is most commonly located on an external wall, usually around the back of the house out of sight, however some systems can be installed internally such as a cupboard or ceiling. 

When installed internally, a flue system is put in to ensure combustion is removed from your living space.

The temperature can be controlled in several ways, such as a controller which the owner can adjust up to 55C (domestic), a temperature preset by the installer or some systems have an app.

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