It is generally held that it takes the same amount of power to heat a given amount of water to a certain temperature. The advantage of tankless technology over the tank type water heaters is found in the idle periods when no hot water is being used. A tank type of water heater must turn on from time to time to keep the water in the tank at the predetermined heat setting. Even when no one is home, the elements use electricity to heat and re-heat the water, costing you money. Not so with the tankless type. It heats the water on demand. Turn the water off and the heater stops working and stays off until hot water is called for again.