Conventional Water Heaters are the most well-known ones and most likely the kind you are probably most familiar with. They are also called storage tank water heaters. They consist of an insulated tank in which water is heated and kept until ready to be used. There are natural gas water heaters and electric water heaters. Natural gas heaters use less energy but can be more expensive and harder to install. Whether gas or electric, Conventional water heaters should be maintained regularly to operate effiently over time. They should be drained and flushed at least once per year. Depending on how well you maintain, the life expentancy of a conventional water heater is 10-12 years. Please see this interesting video which explains how conventional water heaters operate.