Cool venting gas furnaces are more efficient, and I have neighbors who have them just because they want to. I don’t know why the cool vent can’t also be sent to a chimney or to a roof top vent for convenience sake. The vent is a curiosity because it hisses most of the time.
The flue gas emitted is slightly acidic and lower temperature than 80% furnaces. In a conventional chimney that is not hot enough to produce a “natural draft”, warm air rises, so corrosion of the chimney is a problem. They also produce condensation, which needs to drain or be pumped off. Now, PVC straight up through the roof? Possibly, all the manufacturers have their venting guidelines.