What is a tempering valve? Mother washing child's hands in warm tempered water

What is a Tempering Valve and Do I Need One?

Did you know that it’s an Australian regulation to have a tempering valve installed? Like most people, you might be wondering, what is a tempering valve? Here’s everything you could ever want to know.

What is a Tempering Valve?

Tempering valves limit the temperature of hot water systems in Australian homes. More specifically, fixtures that use hot water for personal hygiene purposes, for example, the shower.  It only takes half of a second for 70°C  hot water to give a child third-degree burns. 

The Plumbing Code of Australia mandates that specialists must set the thermostat of tank-based hot water systems to 60°C or higher to inhibit the growth of harmful bacteria like Legionella. The risk of burns necessitated balancing ‘the requirement for minimising the risk of bacterial infection. As a result of this, the installation of a full hot water tempering valve, which restricts the hot water usage to a maximum of 50°C became a mandated rule.

Understanding the Different Valve Types

It’s worth knowing and noting that there are four main tempering valve types. You can easily identify them by the colour of their caps, and manufacturers design them to work with various hot water system types. These include:

  • Orange cap tempering valve: for use with solar powered or heat pump storage tanks
  • Black cap tempering valve: typically installed in large capacity systems
  • Green cap valves: Used in gas powered hot water units
  • Blue cap valves: Used in electric water heaters

Only homes that have a storage tank for their hot water need a tempering valve. Homes with tankless continuous flow models don’t need these valves. This is because there is no stored hot water which is prone to Legionella bacteria growth.

How Does a Hot Water Tempering Valve Work?

For something that can control hot water temperature, tempering valves are quite simple in how they work. They are a three-way mixing valve. One allows hot water in, a second pulls cold water in from the water supply, and the third is the exit for the 50°C water. As the system lets in hot and cold water, it adjusts the temperature before letting out the tempered water.

Preventing Accidental Scalding and Bacterial Growth

Inside the valve is a thermostatic element. A temperature-sensitive element, submerged in water, responds to changes in water temperature. In response to these changes, the thermostatic element expands and contracts. This motion controls a piston that opens and closes the three inlet and outlet valves. Through piston action, the system selectively mixes hot water with cold water until it reaches 50°C. Only then does it open the outlet valve to deliver hot water to the fixture.

The thermostatic element is accurate within 3°C. This means that the temperature of the hot water emerging from your fixture’s tap will be within plus or minus 3°C of the set temperature.

Where is the Tempering Valve Located?

Installers typically fit most tempering valves into the hot water system, and they must also install isolating valves, line strainers, and check valves at the cold and hot water inlets. Depending on the water pressure, you might also need to install pressure-reducing valves.

Before installation even begins, you need to flush the plumbing system to prevent a build-up in the valve. This build-up will not only impact the performance of the tempering valve, but it will potentially void the warranty as well!

You must always have a licensed plumber install a new hot water system and tempering valve.

Can You Adjust Tempering Valves?

You can adjust your hot water system tempering valve using a knob to any temperature between 35-55°C. However, a licensed plumber must make the adjustments, ensuring they do not exceed 50°C.

If you choose, however, your tempering valve can be set lower than the 50°C maximum! For example, if you’re installing a hot water unit that young children or elderly people will be using, perhaps consider a thermostatic mixer. We’ll be touching on this hot water valve shortly.

What Happens When a Tempering Valve Fails?

Given that the tempering valve regulation was introduced to avoid scalding from too hot water, you might worry about it failing and hurting your family during daily personal hygiene purposes. As water temperature increases, the contact time required to receive a third-degree burn decreases:

  • 70°C – 1 second for an adult, 0.5 seconds for a child
  • 60°C – 5 seconds for an adult, 1 second for a child
  • 55°C – 30 seconds for an adult, 7 seconds for a child
  • Less than 50°C – approximately 5 minutes for adults and children

Thankfully, most tempering valves have a thermal shut-off feature. This effectively closes the cold and hot water inlet valves in event of a problem. If this isn’t the case with yours, you will at least be able to notice when your hot water storage system is hotter than usual.

If your tempering valve does fail and you notice your water temperature higher than normal, you should contact a professional plumber to fix the problem. Until you’ve solved the problem, be sure to monitor any children when they are using hot water.

How Long Do Tempering Valves Last?

Much like your hot water system, your hot water tempering valve will deteriorate over time. Provided you keep up with your plumbing maintenance, you can expect it to give you a good 5-8 years of safely heated water.

We find that a build-up of minerals and other materials is the most common reason for replacing tempering valves for hot water systems. Carried in the hot and cold water that moves through your plumbing, these minerals and other materials accumulate in your pipes and fixtures over time. This accumulation eventually impacts the performance of the hot water mixing valve in your fixture, and in severe cases will stop it from working entirely.

This is why your plumbing system needs to be properly flushed by a plumber before they even begin installing a tempering valve. Regular flushing will also help to prolong the life of your valve as well as other plumbing fixtures!

Filters are often recommended to be installed to prevent the build-up from occurring in the first place. An older hot water system and its associated tempering valve are especially prone to rust and build-up and so should be checked more regularly.

Tempering Valve Vs. Thermostatic Mixer

As we attempt to answer the question of “What is a tempering valve?”, it’s important to note that the similar thermostatic mixing valve (or TMV) also exists. Both are designed for mixing hot and cold water to regulate hot water tank temperature. So when it comes to determining whether you need a TMV or tempering valve, it helps to understand the differences between the two and what they do for your hot water supply.

Domestic homes require a tempering valve. However, businesses that care for children and the elderly, such as child care centres, secondary schools and nursing homes, use a thermostatic mixing valve.

A thermostatic mixing valve works by the same mechanism as a tempering valve, but is both more accurate and faster to deliver a safe temperature. Water temperature coming from a tempering valve is accurate within 3°C, while a thermostatic mixing valve, is only out by 1°C! In addition, thermostatic mixing valves must be set no higher than 45°C.

This lower temperature is important for those with more compromised or sensitive skin, such as those in nursing homes. 45°C is a much safer temperature to prevent damage and injury here.

Hot Water System Replacements

When considering a hot water system replacement, it is essential to recognise the critical role of tempering valves. These valves are instrumental in regulating the water temperature to just below the boiling point, ensuring safety and efficiency. The process of hot water system replacements involves the selection of a suitable unit. It also necessitates a thorough understanding of the existing plumbing framework to guarantee a seamless transition. When you hire a skilled service for your hot water system replacement, they will correctly install all components, including tempering valves, and ensure they function at their optimal capacity.

Need A Tempering Valve Installed?

Read Hot Water Systems: The Complete Guide to learn more about the best hot water system for your home. Contact Metropolitan Plumbing for your local heated water tempering valve experts.

Published: 2020-07-17

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