Conventional Water Heater
A storage water heater operates by releasing hot water from the top of the tank when you turn on the hot water tap. To replace that hot water, cold water enters the bottom of the tank, ensuring that the tank is always full. A residential water heater may store from 20 to 80 gallons of hot water, while a commercial storage water heater can range from 20 to hundreds of gallons. A high-efficiency model can reduce water heating bills by about 7 percent and should last about 11 years.
Tankless Water Heater
Demand water heaters heat water directly without the use of a storage tank. Therefore, they avoid the standby heat losses associated with storage water heaters. When a hot water tap is turned on, cold water travels through a pipe into the unit. Either a gas burner or an electric element heats the water. As a result, demand water heaters deliver a constant supply of hot water. However, a demand water heater's output limits the flow rate. A tankless water heater has a life expectancy of 15-20 years and may reduce water heating bills by as much as 30 percent.