In most cases when we install a water heater we will replace the old unit with the same type of unit that is in need of replacement. There are advantages to both gas and electric water heaters that will vary with the individual needs of each homeowner. While an electric water heater will have a lower initial cost for the tank itself, a gas water heater is going to save you money over time with increased efficiency.
The biggest challenge in converting an electric water heater to gas is hooking up the vent and running the gas line. This is easier in some houses than others and will usually require a licensed plumber to come out to determine if it is possible. Another thing that is important to consider is the sizing of you incoming gas line. Your gas supply line may not be sized properly to handle any additional load. This is also something that should be examined by a trained professional.