This is a Trane furnace.
Please take a look at the picture. On the left side of the top picture you can see the large PVC pipes. My understanding is the one is to intake combustion air and the other is to exhaust combustion gases. In the second picture you can see that the two pipes tie together just before they exit through the roof. On the roof, there is simply an open pvc pipe that will allow rain water in. This just doesn’t seem right to me. Am I missing something?