There exists a wide variety of water heaters encompassing various types and sizes, ranging from the conventional storage tank models to the contemporary wall hung tankless models. Both styles can be fuelled by electricity, natural gas, or propane. Selecting the appropriate size and/or power source depends on your specific requirements and the infrastructure of your building, including the availability of gas and the capacity of your electrical system.  Based on your specific demand and peak usage times  for your home or business needs the correct size will be determined by a professional.  Should both fuel options be available calculations can be made to determine which is most efficient long term while considering your budget for the total investment costs involved in installation.