Conventional or storage water heaters - gas or electric typically last between eight and ten years on average . Tank size varies from 30 gallons up to 80 gallons for residential use and more than 100 gallons for commercial purposes. Warranty also varies from 3 years to 12 years, some manufacturers offer lifetime warranty on their electrical brands. Reasons for replacement are leaks, pass the warranty, not enough hot water, need of bigger tank or more efficient unit. Call us if it's time! We will help you choose and install the right one for you for reasonable price and in short time manner.