Tank water heaters heat water and store it in the tank for use when needed. These types of water heaters come in different sizes from 30-75 gallons – the size needed depends on household size and consumption. Tankless water heaters, also known as on-demand water heaters, do not heat water ahead of time and hold it in reserve. Rather, the water is heated as soon as your fixtures or appliances call for hot water.
Both tank and tankless water heaters run by gas or electricity.