Both instant and storage water heaters generate hot waters, but their attributes and features differ.
There are 3 types of instant electric water heaters: mechanical, electronic and digital. The mechanical kind is the least expensive and features step-less control. Electronic type lets you control the power setting while digital type comes with a temperature display panel besides having power setting control. The instant water heater operates with a 3-3.3kw element and generally works for individual supply points, therefore if you have 2 bathrooms, you will need 2 instant water heaters. Unlike storage water heater, instant water heater does not require pre-heating before using as it generates hot water instantly. The water temperature can vary according to the water pressure. For example, if water pressure is low, the water temperature will go up and vice versa. The average life span for an instant water heater is around 3 to 5 years.
A storage water heater has an inner tank for storage of water. The capacities range from 15 litres to 100 litres. The inner tank can be made with stainless steel or copper. It operates with a 1.5kw to 3kw element and can supply hot water to more than one point (multi-point system), which means that it can supply hot water to more than 1 bathroom as well as kitchen simultaneously. A mixer is used to regulate and provide constant water temperature so it is not affected by the change in water pressure. However, the water stored need to be pre-heated before used. To save energy and prevent loss of heat, insulation is placed between the storage tank and outer casing of the heater. A storage water heater also comes with an automatic thermostat to cut off the power supply when it reaches the preset temperature. Therefore the additional electricity consumption for switching the heater on the whole day is negligible. The average life span for a storage water heater is around 5 to 7 years.