The temperature range for the growth of Legionella bacteria in water, according to the HSE, is generally between 20-45°C, so tap water should ideally be kept either above 50°C or below 20°C. Legionella dies at temperatures above 60°C, and hibernates at temperatures below 20°C. In practice, the growth rate is so low at temperatures up to 25°C that, for example, Safe Water states that cold water temperatures of up to 24°C within 8 hours are acceptable for pipe shafts containing hot water circulation (HWC). The time scale for significant Legionella growth in water systems is in the order of days to weeks.
Enduce floor drain heats incoming cold water to a temperature typically between 30-35 C just before the cold water is flushed out of the shower head. The heating only takes place during showering, which gives a very short heat retention time before the water reaches the thermostatic mixer (seconds). When showering ends, the heat exchanger cools down quickly (<3 h) to a temperature 25 C and residence times on the time scale of days-weeks to reach problematic levels. Cooling time and temperature have been verified by independent tests at RISE after showering at 40 C.
The floor drain installation instructions state that no underfloor heating may be installed on top of the floor drain space for the heat exchanger in order to completely avoid the risk of the floor drain installation contributing to Legionella growth.
In summary, from a Legionella perspective, the Enduce floor drain is significantly safer than insulated cold water pipes run in conduit shafts together with HVAC pipes.
