Free tool · Checker
Temperature danger-zone checker
Type a stored or outlet temperature to see where it sits against the commonly cited control figures. Updates as you type.
Legionella multiplies fastest between 20 and 45°C. Drag the bar or type a reading.
The commonly cited figures
- Below ~20°C: Legionella is largely dormant, keep cold water below this.
- ~20–45°C: the growth range, the zone to avoid in stored or stagnant water.
- ~50°C+ at outlets, ~60°C stored: the hot-water control regime.
Guidance figures, not a verdict on your system; your risk assessment sets the targets. Source: HSE, HSG274 Part 2 (2024), ‘Operation and inspection of hot and cold water systems’, p.70. Mind scald risk where vulnerable people are exposed.
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"Legionella temperature danger-zone checker." Legionella.io. https://legionella.io/tools/temperature-checker/
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