Where are thermostatic mixing valves mandatory in Australia?

Under NCC 2025 B2D5 and B2D6, thermostatic mixing valves (TMVs) complying with AS 4032.1 are mandatory at personal hygiene outlets in aged care facilities, healthcare patient care areas, early childhood centres, primary and secondary schools, and accessible sanitary facilities in Class 2-10 buildings. These locations must deliver water at no more than 45 degrees C.

What is the difference between a TMV and a tempering valve?

A thermostatic mixing valve (TMV) to AS 4032.1 holds temperature within plus or minus 2 degrees C and has a fail-safe shutoff that cuts hot water flow if the cold supply fails. A tempering valve to AS 4032.2 is less precise (plus or minus 3 degrees C) and has no thermal shutoff. TMVs are required where the delivery limit is 45 degrees C. Tempering valves are acceptable where the limit is 50 degrees C.

What are the hot water temperature limits under the NCC?

NCC 2025 B2D5 sets two limits. Personal hygiene outlets in aged care, healthcare, childcare, schools and accessible facilities must not exceed 45 degrees C. All other personal hygiene outlets must not exceed 50 degrees C. Hot water storage must be at least 60 degrees C to prevent Legionella growth, per AS/NZS 3500.4.

How often do TMVs need testing and maintenance?

AS 4032.3 requires TMV field testing at intervals not exceeding 12 months. A major service including replacement of thermostatic actuators, o-rings and seals is required every 5 years. All testing must be carried out by a licensed plumber and results recorded per AS 4032.3 Appendix B.

Can I use a tempering valve instead of a TMV in a commercial office?

For standard staff amenities in a commercial office, a tempering valve to AS 4032.2 is acceptable for the 50 degrees C limit. However, accessible bathrooms in the same building require a TMV to AS 4032.1 with a 45 degrees C limit. Most commercial buildings have accessible facilities, so at least some TMVs will be needed.

Thermostatic Mixing Valve Requirements

Section 1

What You Need to Know

Hot water stored below 60°C grows Legionella. Hot water delivered above 50°C scalds skin. A thermostatic mixing valve (TMV) sits between the two problems. It blends hot and cold water to deliver a safe temperature at the tap while the system stores water hot enough to kill bacteria. The NCC and AS 4032.1 set the rules for where TMVs are mandatory, what temperature they must deliver, and how often they need testing.

Section 2

The Rules

Hot water must be stored at 60°C minimum to prevent Legionella growth (AS/NZS 3500.4, Cl 1.9)
Delivery temperature must not exceed 45°C at personal hygiene outlets in aged care, healthcare, early childhood centres, primary and secondary schools, and accessible facilities (NCC 2025, B2D5)
Delivery temperature must not exceed 50°C at personal hygiene outlets in all other buildings (NCC 2025, B2D5)
Where the limit is 45°C, the temperature must be controlled by a TMV complying with AS 4032.1 or a thermostatically controlled tap (NCC 2025, B2D6(1))
Where the limit is 50°C, a tempering valve to AS 4032.2, TMV, thermostatically controlled tap, or temperature-limited heater may be used (NCC 2025, B2D6(2))
All TMV field testing, maintenance and replacement must comply with AS 4032.3 (NCC 2025, B2D6(4))

Section 3

What This Means in Practice

Take a 40-bed aged care facility with ensuites in every room. Each ensuite basin and shower needs water at or below 45°C. That means a TMV at every outlet - or a group TMV serving a cluster of fixtures on the same branch. The hot water plant stores at 60°C for Legionella control. The TMV blends that down to 45°C at the point of use.

A TMV holds temperature within ±2°C. If the cold supply fails, the valve shuts off hot water flow within seconds. This fail-safe is the main reason AS 4032.1 exists. A tempering valve (AS 4032.2) does not have this shutoff. It keeps on delivering - potentially at full hot water temperature. That is why tempering valves are not allowed where vulnerable people use the water.

Now consider a standard office building with staff amenities. The 50°C limit applies. You can use a cheaper tempering valve here, or a temperature-limited water heater. But if the building has an accessible bathroom - and most commercial buildings do - that fixture needs a TMV to AS 4032.1 and a 45°C limit. One accessible basin in a 10-storey office means at least one TMV per accessible amenities group.

Dead legs matter. Any branch pipe between the TMV and the fixture should be no longer than 1.5 metres. Longer runs cool the water below a useful temperature and create stagnation zones where bacteria grow. In large buildings with circulating hot water, position TMVs close to fixture groups to keep dead legs short.

Section 4

Key Design Decisions

1

Individual TMVs vs Group TMVs

Install an individual TMV at each fixture for the tightest temperature control. Or use a group TMV serving 2–4 fixtures on the same branch to reduce valve count and cost.

Trade-off: Individual TMVs cost $150–300 each installed. Group TMVs reduce hardware, but a single valve failure affects every fixture on that branch. In hospitals, individual TMVs are standard practice.

2

TMV Location and Access

Mount TMVs where a plumber can reach them for annual testing. Under basins, in duct risers, or in ceiling voids with access panels all work - but they must be accessible without removing wall linings.

Trade-off: Concealed TMVs look cleaner but make maintenance harder. Budget for access panels at every TMV location. Miss this in design and the plumber cuts holes during the first service visit.

3

Tempering Valve vs TMV in General Areas

Use tempering valves (AS 4032.2) for standard staff amenities at 50°C. Use TMVs (AS 4032.1) for any fixture at 45°C - aged care, healthcare, childcare, schools, and accessible bathrooms.

Trade-off: Tempering valves cost roughly half the price of TMVs. But using TMVs everywhere simplifies the specification and removes the risk of installing the wrong valve type on the wrong fixture.

4

Circulating Warm Water Systems

In large buildings with long pipe runs, install a warm water circulation loop downstream of the TMVs. This keeps water at the right temperature at the tap without long wait times.

Trade-off: Circulation pumps add $2,000–5,000 per loop and need energy to run. But without circulation, users run taps for 30–60 seconds waiting for warm water - wasting water and creating complaints.

Section 5

Who Needs to Know What

Section 6

References

AS/NZS 3500.4:2021, Plumbing and drainage — Part 4: Heated water services
AS 4032.1:2005, Water supply — Valves for the control of heated water supply temperatures — Part 1: Thermostatic mixing valves — Materials, design and performance requirements
AS 4032.2:2005, Water supply — Valves for the control of heated water supply temperatures — Part 2: Tempering valves and end-of-line temperature control devices
AS 4032.3:2022, Water supply — Valves for the control of heated water supply temperatures — Part 3: Requirements for field testing, maintenance or replacement of valves, taps and devices
National Construction Code 2022, Volume Three, Part B2 — Heated water services
National Construction Code 2022, Volume One, Part F4 — Sanitary and other facilities
ABCB Handbook: Warm Water Systems (2020)

Thermostatic Mixing Valve Requirements

What You Need to Know

The Rules

What This Means in Practice

Key Design Decisions

Individual TMVs vs Group TMVs

TMV Location and Access

Tempering Valve vs TMV in General Areas

Circulating Warm Water Systems

Who Needs to Know What

Need this engineered for your project?

References

Related design memos

Hot and Cold Water System Design

Domestic Hot Water Plant Sizing for Commercial Buildings

Legionella Risk in Hot Water Systems