Heat top half of tank

[Matthen]

Hi -
I've got a dual element E7 vented hot water system. Currently, the immersion heater at the bottom heats the tank every night - assuming minimal hot water usage, it uses between 2 and 3 kWh every night. Thing is, I don't use much hot water - I have a dishwasher and electric shower - I imagine I use less than 20 L a day, unless I bath.

If I swap the wiring over, so I only heat the top half of the tank, and then "boost" the bottom when I fancy a bath, will there be a risk of legionella growing in the bottom half of the tank? Top half will be heated to 65*C (ish). I suspect doing this will half the power draw from the cylinder, which could be a significant saving next year.

 

[Ric2013]

The main risk with legionella is from a shower anyway - and yours is electric. Even if there were legionella in the water at the bottom of the cylinder, you are drawing off the hot water from the top which, being maintained at 65, won't contain legionella. The water isn't stagnating as you are using some water every day.

In practice, MOST cylinders will have a certain amount of water at the bottom that sits at 40° or so. My inclination is to say that provided the cylinder is genuinely heated through at least once a week there isn't an issue.