Question: how many watts does a 40 gallon hot water heater use?
Answer: A 60-gallon (270-litre tank) with 4,500 watts in heating power will produce 259 litres of hot water during this first hour. A 40-gallon (180-litre tank) with heating power of 3,000 watts will provide 173 litres of hot water. A bath requires an average of 50 to 70 litres of hot water, and a shower takes 40 to 60 litres.