We have had as many as thirty in stock at a time in our warehouse.
Gas waterheaters (natural gas or propane) are atmospheric ventilation models, meaning they use a galvanized vent pipe inserted into a masonry chimney.
Power-vent waterheaters are the same as the atmospheric models, but with a re-engineered exhaust system. The outlet is formed of PVC rather than metal and features a blower (black motor at the top) to assist remove combustion by-products and may be drained through the roof or side walls without a chimney.
Electric waterheaters because the name state… It might have an electrical wire connecting to the highest point of the waterheater. They would even have one or two access doors (as shown in the photo) on the front of the unit.