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Outlet flushing time calculator

A little-used outlet should run long enough to draw fresh water through and clear what has been standing in the branch. This works out that standing volume and the time to displace it.

Bore of the branch pipe, not the outside diameter.
mm
From the live circulating pipe out to the outlet.
m
Measured at the outlet, fully open.
L/min
How to read this

The volume is the water standing in the branch between the live pipework and the outlet. Displacing one volume is the bare minimum to draw fresh water through. In practice, run the outlet until the temperature stabilises, often two to three volumes, before recording any check.

A planning aid, not a substitute for a competent, site-specific risk assessment, which sets your flushing regime. Source: HSE, HSG274 Part 2 (2024), ‘Operation and inspection of hot and cold water systems’, p.70.

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"Flushing time & volume calculator." Legionella.io. https://legionella.io/tools/flushing-time-calculator/

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