Definition. A BTU is the quantity of heat needed to raise one pound of water by one degree Fahrenheit. More BTUs mean more heating power.Click to see full answer. Similarly, you may ask, how many BTU’s do I need for my hot water heater?Input ranges from about 32,000 on a 30-gallon unit to 88,000 on a 100-gallon tank. A common input is 34,000 BTUs on a 40-gallon tank and 36,000 BTUs on a 50-gallon tank. The higher the BTU input and efficiency, the faster the recovery. Electric water heaters typically have one 5,500-watt or two 4,500-watt elements.Also Know, what is BTU stand for? British Thermal Unit Similarly, it is asked, what does BTU mean for water heaters? British Thermal Units Is a 50 gallon water heater enough?A 50 gallon water heater is the most common tank we install. It is such a common size because it can supply hot water for 3 – 5 people. Considering an average shower uses 17.2 gallons of water you can typically have enough hot water for up to five people to take a shower within an hour.