100 litres at 60 degrees Celsius = 1 hour (2kw element)
150 litres at 60 degrees Celsius = 1.5 hours (3kw element)
200 litres at 60 degrees Celsius = 2 hours (4kw element)
250 litres at 60 degrees Celsius = 2.5 hours (4kw element)
provided all are using 220 volts of domestic electricity