A power vent water heater means you do not have to have a chimney to vent through the roof of your home. The venting is done through PVC or ABS pipe that can exit the house at ground level. The word "power" simply refers to the fact that it uses a fan on top of the heater to push the hot air out. I think the small tube is what tell the fan to activate. You treat a power vent heater exactly the same as any other type of water heater. If you shut the gas off, it will not heat water until you turn the gas back on. They use an ignitor plate rather than a standing pilot light.