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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.

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

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 result is the theoretical standing volume in the entered pipe geometry and the time one nominal volume would take at the measured flow. It does not set a flushing duration or prove that a temperature or water-quality end point has been reached.

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/

Free to reuse under CC BY 4.0: quote, adapt or republish with attribution and a link back to the original.

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