A water heater's energy efficiency is determined by the energy factor (EF), which is based on the amount of hot water produced per unit of fuel consumed over a typical day. The higher the energy factor, the more efficient the water heater.
EcoSmart 27 kW Self-Modulating 5.3 GPM Electric Tankless Water Heater
I think it would be really nice to have this instead of that huge tank in my basement. Just one more natural gas thing to get rid of. EcoSmart 27 kW Self Modulating GPM Electric Tankless Water Heater-ECO 27 at The Home Depot
Cut Costs by Choosing the Right - Cut your utility bills by the correct water heater for your home and family. Consider factors such as home size, number of people and source when searching for the right model.
Pros and Cons of Tankless Water Heaters: Tankless water heaters can save energy, but at a higher initial cost and they serve hot water one faucet at a time—so someone gets a cold shower if multiple showers are running.
DIY Solar Thermal Water Heater: Free Hot Water For Life