Two years 11/2 months and PhenQ Reviews 3 days and 41/2 hours approximately.It has to do with how many thousands of gallons are in the tank , how many are being drawn out and what the BTU input is of the fuel being used100 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