Tankless water heaters are hear to stay. In their first few years, there were bugs that had to be worked out, as there is with any new product. Now, I haven’t had any problems with them in years and they are in all of our new homes. How do they save energy and money? Regular tank water heaters have to keep 50 gallons or so of water heated 24/7, even when not in use. Tankless models only turn on when there is a demand (When you turn on a hot water faucet). At that time, they instantly come on and run as long as needed, then they shut off again. As long as the water heater is working, you’ll never run out of hot water. You could have 3 kids all taking showers while running laundry and the dishwasher. Yes, they are more expensive than the tank water heaters, but over time, you get your money back in fuel savings, plus there is less maintenance. Whether they are installed in the attic or on the side of a home, there should be a drain line going to the outside, as well as a pressure relief valve in the event of too much pressure build up.