Gas water heaters (natural gas or propane) It is an atmospheric ventilation model which means it uses a galvanized ventilation pipe connected to the masonry chimney.
Power-vent water heaters They are similar to atmospheric models, but with a reconstructed exhaust system. The exhaust is made of PVC plastic instead of metal, has a blower (black motor on top) installed to help expel burning by-products, and can be vented through the roof or sidewall when there is no chimney.
Electric water heaters As the name implies… there are wires connected to the top of the water heater. They will also have one or two entrances to the front room (as shown in the picture).