Water heater capacity is chosen according to the number of users, their water consumption and the house’s sanitary facilities (bath, shower, etc.). It also depends on the water temperature when it arrives in the water heater, influencing on time for the water to get heated up. As a general rule, we recommend larger tanks when your family is located in cold weather countries (Estonia, Germany, etc.), and smaller tanks when you are located in warmer climates countries (Vietnam, UEA, Urugay, etc.). As an example, we would recommend a 50L water heater for a family of 4 people in a warm country; and a 150L water heater for the similar family located in a colder region of the world. For more detailed advice, contact your local dealer.