A tankless water heaters uses 30 to 50 percent less energy than units with tanks, saving a typical family about $100 or more per year, depending on water usage. Tankless units (also called “on demand” units) heat water only when you turn on the faucet. They usually operate on natural gas or propane. The main advantage is that they eliminate the extra cost of keeping 40 to 50 gallons of water hot in a storage tank, so you waste less energy. They also offer a continuous supply of hot water, which is ideal for filling a big hot tub or a whirlpool. They're more compact than a standard water heater and mount on a wall.
TRADITIONAL WATER HEATER
Which one should I choose? Generally, traditional tank type water heaters have a lower initial purchase price. Also, depending where the water heater is located, the installation of a new tank-type water heater tends to be less expensive.
If there is an electrical power outage and you have a gas powered water heater, you will still have hot water, as long as there is still gas flowing to the unit.