If your heater location has adequate air supply, and is not in a hazardous location ,i.e. a bedroom, then the power vent models will be sufficient. They are all about the same efficiency. If you also need to supply safe combustion air then you need a direct vent, and there is only one of those available for residential use.: Im looking for a new gas water heater that I can vent directly outside (i.e. no chimney needed). I know I need a Side-vented one (either power-vent or direct-vent) Is there some place I can find a listing of brands available and a comparison between them (including efficiency ratings)?