Tankless Water Heaters provide hot water only when there is a demand for heat. The first thing that you need to consider when decide to buy a tankless water heater is the fuel type: Electric, or Gas-Fired Tankless Water Heater. The next important thing is you need to consider where you will need hot water: at one bathroom sink, an entire bathroom, or an entire house. When selecting a contractor, don’t forget to request for the cost estimates in writing, and the warranty information.