The conventional water heaters are the gas and the electric type ones. An electric water heater can be used almost anywhere. A gas water heater is most likely to be installed in a home that already uses gas for another appliance such as a furnace or stove.

Building codes may dictate the placement of gas water heaters, restricting them to areas outside of normal home activity.

It is likely that if you are replacing a water heater, you'll simply replace it with the same type of unit that was already there. There may be exceptions to this rule, however, for a variety of reasons. In any case, if you choose to replace an electric unit for a gas unit–or vise versa–bring in a professional to do the job. Installing or removing gas lines is not a project for the do-it-yourselfer.