Function

• The Rinnai tankless water heater provides hot water on demand by heating as much as you need when you need it. When a hot water tap is opened, the heater begins the heating process. Water is heated to the desired temperature as it moves through the copper heat exchanger. This eliminates continuously heating a a tank of water waiting to be used, and having only as much hot water as a hot water tank can hold, according to the Rennai website.
  
  

Significance

• Energy costs are reduced by 40 percent. This is because when the need for hot water stops, the tankless hot water heater shuts down, using almost no energy, while a tank style heater still requires energy to keep the water hot.
  
  

Considerations

• Rinnai tankless water heaters usually last up to 20 years when installed in the home. This is about twice as long as a tank style water heater. Additionally, there is no tank to break down or leak.
  
  

Features

• Little space is required to install the Rinnai tankless water heater. The tank style can take up about 16 square feet, while the Rinnai is about the size of a small carry-on suitcase and can be installed on any wall.