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.
Based on HSG274 Part 2. Your site's risk assessment decides what applies.
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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