Why hot water is stored at 60 °C, distributed hot, and how dead legs are limited.
Storage, distribution and delivery are different checks
In a conventional temperature-control regime for Legionella, store hot water at least at 60 °C. The unblended hot supply should reach at least 50 °C within one minute at outlets; the corresponding healthcare target is 55 °C. A secondary circulation return should meet its specified return temperature, normally at least 50 °C in the general regime.
At a TMV, measure the hot inlet for the distribution check. The blended outlet is checked separately against the scald-control setting. Do not raise a protected bath or basin to 50 °C merely to satisfy the hot-distribution test. Where vulnerable people are at risk during whole-body immersion, delivered water must not exceed 44 °C and may need to be cooler.
Use actual measurements at the appropriate points. Measure the stored temperature instead of trusting the thermostat setting. A good reading at the cylinder does not show that every distribution branch is controlled. Other validated hygiene strategies require their own design, monitoring and corrective actions.
Avoid stagnant branches
Keep outlet branches and blended-water runs short and ensure suitable turnover. A branch serving a frequently used tap is not the same as redundant pipework or a branch whose outlet is rarely used. Remove unnecessary blind ends and manage little-used outlets with the specified flushing regime. A main circulation loop cannot refresh a branch through a closed outlet.
Estimating standing-water clearance
Divide the volume drawn by the pipe’s volume per metre to find the equivalent length emptied. This is an ideal volume calculation, not an allowable branch-length rule or proof of the temperature that will arrive.
Worked example. A tap running at 2 litres a minute draws 2 litres in one minute. If the branch holds 0.05 litres per metre, that volume occupies 2 ÷ 0.05 = 40 m. The arithmetic does not recommend a 40 m branch. Supply temperature, pipe heating, mixing, actual flow and the need to minimise stagnation still govern the design and measured response.
On a short spur close to a circulating return, HSG274 expects hot water much sooner: under 30 seconds, typically 10 to 20 seconds. A slower response can indicate a return fault. Check temperatures, flow, branch volume and circulation before deciding why the result is slow.