Elgas LPG Gas Blog

Tempering Valves for Hot Water Heaters

Scalding is one of the most serious, painful and long-term injuries for young children. 

Scalding can happen very quickly, depending on the temperature of the water. 

Scalding Hazard

However, at 50°C a serious burn wouldn’t typically happen until after 5 minutes, so you can see the benefit of controlling the temperature of the hot water at the tap.

Conflicting Requirements

Prevent ScaldingFor example, at 60°C a serious burn can occur in 1 second.  
The Plumbing Code of Australia (PCA) has two conflicting requirements. 
To protect against the growth of Legionella bacteria, the cause of Legionnaires’ disease, it is a legal requirement that any stored hot water be kept at a minimum temperature of 60°C. 
This requirement is as per Australian Standard AS3500.4.2 Clause 1.6. 
This applies to all hot water systems with tanks, including solar and heat pumps.
On the other hand, the Code requires that the delivery temperature of hot water for personal hygiene purposes (primarily bathroom taps) is not to exceed 50°C. 
The maximum temperature is 45°C for early childhood centres, primary and secondary schools, and nursing homes or similar facilities for young, aged, sick or disabled persons.  
So, how are both of these requirements met?

Tempering Valves (Hot Water Mixing Valves) Explained

Tempering ValveA tempering valve mixes your hot and cold water to deliver hot tap water at a constant temperature.  
Tempering valves have a temperature sensitive element which adjusts the mix depending on the temperature of the incoming water flowing through the valve. 
The mechanism is a sliding valve that varies the ratio of hot and cold water that is allowed to pass. 
The valve is designed to maintain a constant outlet temperature, reducing the risk of accidental scalding.  
Your plumber adjusts the valve to the required temperature. 
The temperature is typically controlled to within ±3%.

Tempering Valves & Thermostatic Mixing Valves Now Required

The PCA now requires that tempering valves be installed on all new homes or renovations. 
So, when replacing an old hot water system you must now install a tempering valve to reduce the temperature to 50°C in bathrooms. 
Kitchen and laundry applications are still permitted to bypass the tempering valve and use the hot water directly from a standard electric or gas hot water tank. 
Please see the tempering valve flow chart below.
Thermostatic mixing valves are required for the previously mentioned facilities that require 45°C. 
Thermostatic mixing valves are faster in responding to temperature and pressure changes and typically limit output temperature variances to ±1%.
The exceptions to this rule are tankless continuous flow hot water systems. These are LPG or natural gas powered.
As they have no tank in which Legionella bacteria can breed, they do not have to be set at 60°C.  
Typically, they are factory pre-set to 50°C.  As a result, no tempering valve is required.

Types of Tempering Valves

There are different types of tempering valves for different types of hot water heaters. 
The two primary differences are the incoming hot water temperature and pressure. 
These different types of tempering valve are colour coded by application:


This is the most common type of tempering valve and is used with electric water heaters that typically supply hot water between 65°C and 75°C.


This valve is designed for most types of gas hot water systems, including gas storage and tankless continuous flow models. 
However, remember that 50°C factory pre-set models do not usually require a tempering valve.


This high performing valve is for use with solar hot water and heat pump hot water systems, where the incoming hot water temperature can approach boiling point.


These are suitable for large capacity and low pressure gravity feed systems.
While there is no finite life span for tempering valves, some manufacturers suggest that they be replaced every 5 years.  
Thermostatic mixing valves are usually serviced much more frequently, although not necessarily replaced.
If you have an older hot water system, you may not have a tempering valve.  However, they can be added to older systems, too.  
Please consult with your licensed plumber for all tempering valve installation and maintenance issues.
Tempering valve flow chart
Picture source: VIC PIC 

Tankless Continuous Flow Hot Water


Traditional Hot Water Tanks

When it's time to get a new hot water system, two of the most asked questions are:

1.  “Should I get a traditional hot water tank or a tankless continuous flow system?”

2.  "What size hot water system do I need?"

We review the two hot water system types and compare the pros and cons of both, as well as the prices, to help you make an informed decision.

We also explain hot water heater sizing.

Both types of heaters supply hot water but they do it in different ways. 

Let’s look specifically at the points of difference:

Running Out of Hot Water

Traditional hot water tank heaters can only heat a certain number of litres at a time. 

Residential hot water heaters are typically in the 135L to 170L range. 

Off-peak electric units need to have a much larger capacity, as they have to last through the entire day.

Once all of the hot water in the tank is used up, it takes time to heat up the fresh water entering the tank. 

If it runs out right in the middle of a shower, you have an uncomfortable problem. 

You can finish with a cold shower or just stay soapy while you wait for the water to reheat. 

Neither is a good choice.

With a tankless continuous flow hot water system, the water is heated as you use it. 

The unit can maintain the flow rate indefinitely. 

So, you basically never run out of hot water, no matter how many people get to the shower before you.

Energy Consumption

Tankless gas hot water systems only needs to run when the hot water is actually required and wasteful pilot lights are a thing of the past. 

On the other hand, with a hot water tank, you have to use energy to maintain the temperature of the stored water 24/7. 

The technology and energy saving designs are also very different. 

Modern tankless continuous flow models typically have a 6 Star energy rating. 

There are even 7 Star units now available. 

Tankless systems are available in both natural gas and LPG models.

In contrast, most tank hot water heaters are only rated at 4 or 5 Stars. 

This means both the energy consumption and the running costs will be higher. 

Tank heaters are available in electric, natural gas and LPG models.

So, while we'd love to sell you more gas, we'd rather have you saving money and energy with the more efficient models. 

They are also the best choice for the environment.

Bosch 26eSize and Aesthetics

Storage tank hot water heaters are big, especially the electric off-peak models. 

Even when installed outdoors, the size can get in the way, particularly with today’s smaller lot sizes. 

Having this large object next to your house also does nothing for the appearance of your home.

At about the size of a small suitcase, tankless water heaters are much smaller than a traditional storage tank heater. 

Mounted flush against the wall, the smaller tankless units take up less space and are also more aesthetically pleasing, as they don’t dominate the exterior appearance of your home.

CO2 Emissions

Greenhouse gas emissions are reduced through the use of tankless water heaters. 

Tankless gas hot water systems produce about 75% less CO2 greenhouse gas emissions, when compared to a storage tank hot water systems powered by coal-fired electricity.

Even when compared to gas storage tank units, tankless units are more eco-friendly. 

The 6 to 7 Star tankless models consume less gas and create less CO2.

Life Span

Traditional storage tank water heaters have a life span of around 10 to 12 years. 

Warranties for storage tank units are typically 5 to 10 years.

Tankless hot water systems can last up to 20 years. 

Warranties for tankless units are typically 10 to 12 years.

Water Quality

Water from a storage tank water heater may pick up bits of rust and scale that build up within the tank. 

Since there's no tank to rust and no water stored with a tankless system, the water stays cleaner and fresher.


When you first turn on the tap, there is typically a delay in getting hot water, as the water in the pipes leading from the water heater to the tap will be cold. 

Because it is kept hot, tank systems can be slightly faster in delivering the initial flow of hot water, as the tankless system takes a second or two for the unit to get up to temperature.

However, now there is a new system to eliminate the delay entirely. 

The Rinnai Smartstart® Water Saver was developed to reduce water wastage whenever a hot water is turned on.  It pre-heats the water in the pipes before you turn on the hot tap. 

It is part of the Rinnai Infinity range of tankless systems.

Initial Cost

In the past, there was a substantial difference in the price between tankless and storage tank hot water units. 

However, the days of super cheap 3 Star storage tank units are long gone. 

The difference has now shrunken to the point where there is almost price parity between comparably sized units. 

This is especially true if you are comparing 5 Star tank units to the 6 or 7 Star tankless models.

Health & Safety

Storage tank hot water heaterWith storage tank water heaters, there is the potential for bacteria growth within the tank. 

The World Health Organisation -- WHO -- recommends that stored hot water be kept at a minimum of 60°C. 

Unless a minimum of 60°C is maintained, hot water tanks can be a breeding ground for Legionnaires’ disease, or Legionellosis, that is caused by a bacterium, Legionella pneumophila.  It is a respiratory disease that can cause severe pneumonia and is sometimes fatal.

However, Canadian studies have shown, even when the thermostat is set at 60°C, a high percentage -- approximately 40% -- of electric water heaters remain contaminated. 

This is because of the lower temperature, of about 30°C to 40°C, at the bottom of the tank.

With tankless systems, the prevention of bacterial growth is not an issue, as there is no stored water in which bacteria can breed. 

Tankless systems can also be set at 50ºC, so the risk of scalding is greatly reduced without the need of a tempering valve.


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The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances