TMV (Thermostatic Mixing Valve) and tempering valve
What a TMV and tempering valve do, the 50 degree rule, where each is required in residential.
Ask Chalkline about this →A tempering valve mixes hot and cold water to deliver a fixed maximum temperature at the outlet, typically set to 50°C for residential. A Thermostatic Mixing Valve (TMV) is a more accurate thermostatic device used where the temperature limit is lower (commonly 45°C in healthcare and aged-care settings) and where the standard requires a TMV rather than a tempering valve.
NCC 2022 Volume Three (Plumbing Code of Australia) Part B2 and AS/NZS 3500.4 require a tempering valve set to deliver no more than 50°C at sanitary fixtures used primarily for personal hygiene in residential occupancies. That covers basins, baths and showers. Kitchen sinks and laundry troughs are excluded from the 50°C limit because they are not used for personal hygiene.
The tempering valve sits at the hot-water unit outlet on residential systems. Field commissioning, maintenance and replacement of TMVs and tempering valves follows AS 4032.3:2018. A bath or shower outlet running >50°C at PCI is a defect.
Also known as: thermostatic mixing valve, tempering valve, mixing valve, TMV.
Category: Plumbing.
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Last updated: 2026-05-05. Verified: 2026-05-05.