A properly sized water heater will meet your household’s hot water needs while operating more efficiently. Therefore, before purchasing a water heater, make sure it’s the correct size. An undersized water heater will work harder and have a shorter lifespan.
If you are currently are running out of hot water the recovery rate of your water heater is too slow or the size of the tank is too small. If space allows you should consider increasing the size of the tank.
Sizing a water heater to fit your needs is not hard to do. You do not want to heat a lot of water that you don’t need. On the other hand you want to be sure that you have enough hot water for you and your family.
For tank water heaters, the key criterion is hot water storage capacity. To determine that capacity, you first need to add up about how much hot water your household uses during the busiest hour of an average day. This sum — your household’s “peak-hour demand” for hot water — should be close to your water heater’s “first-hour rating” (FHR) printed on the top left corner each heater’s yellow Energy Guide label. Basically, the FHR tells you how many gallons of hot water a heater can produce during an hour of high usage. It is not the same as the number of gallons a tank can hold. It depends on the tank capacity, source of heat (burner or element) and the size of the burner or element.
Water heater sizing is not an exact science. Always allow yourself a little lead way.Its better to have a little extra hot water than not enough.