Immersion Heater: hot water tanks

kniste

I have a saving tip that does not seem to be used by many,  TO BE USED WITH CAUTION. Building regs dictate that the temperature in the HW water storage tank should be set at 65'c to kill Legionaires bacteria. The tank thermostat is usually in the middle of the tank. this means that (HW rises) the top of the tank where you take the water is usually just below boiling (v Hot). I have set my thermostat to 35'C, this means that the water for my shower emerges at about 40'C. I therefore need very little cold water added, saving water, and power to heat the water. ONCE A WEEK I PROGRAM THE SYSTER TO HEAT THE WATER TO 65'C. this should purge the bacteria. 

FreeBear

Building Regulations 2010 does not specify any temperatures for hot water. The approved document covering sanitation, hot water safety, and water efficiency (often referred to as Building Regs: Part G) draws attention to HSE guidance on the control of Legionella with respect to premises being used for business or trade. HSE only suggests maintaining a temperature of 50-60°C in systems that do not have a high turn over of water.

If you care to read (peer reviewed) studies of Legionella Bacteria in water systems, you will find that it can not survive long above 50°C (a matter of hours). Anything above ~60°C is almost instant death for the bacteria, so no need to go to 65°C.

If your water is supplied by a water company, it will have been treated to ensure it is free of bacteria (not just Legionella), and supplied at a temperature cold enough that any bacteria can not multiply. So unless you are drawing your water from a contaminated source or storing it in an infected open tank, the risk of Legionella is minimal at best. If there is a risk of Legionella, keeping your tank at 30-40°C is right in the zone where the bacteria will multiply - But then you should be having your water tested at regular intervals if the household contains vulnerable residents.