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
Serious burns can occur at 60°C 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
A tempering valve:
- mixes your hot and cold water to deliver hot tap water at a constant temperature.
- 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 to maintain a constant outlet temperature, reducing the risk of accidental scalding.
The valve is adjusted by Plunna Plumbing to the required temperature, typically set 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, 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.
- 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, 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:
Blue
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.
Green
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.
Orange
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.
Black
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 Plunna Plumbing for all tempering valve installation and maintenance issues.