[bestgenman]

Jack, my theory is the AQ and generator exhaust are joined where the gasses are vertically oriented and since hot gasses naturally rise, they go up!  The generator would have to force the gasses 180 degrees downward and into the 1-1/4 pipe and then into a 90 degree elbow, across a fairly long horizontal path and up through another 90 degree elbow into the AQ.  The vertical path has much less resistance.   If, and a very long chance if,  there was a pretty stiff wind right into the turn out at the roof level (for those with roof exhaust) , it would be possible to get some engine exhaust back feeding into the AQ.  In all my years on this forum, I have never read about that happening!

Just saying!