Is it time to replace your old water heater? Consider going tankless. In contrast to traditional hot water heaters, this tankless system from Rinnai heats water only when you need it. This means that you don’t waste energy constantly heating and re-heating water that sits in the storage tank for hours, like when you’re asleep or no one is home. It also means that you don’t run out of hot water. It’s a win-win situation.