Hello. I recently replaced an old FHW boiler in my house with a new Weil McLain WTGO-3. I had it inspected by the town and the only comment the inspector said was that the vent to the chimney flue was not allowed to have a reducer in the path and that the vent pipe should be the same diameter all the way to the flue connection. I can't find all the municipal codes of course but has anyone heard of this?

The WTG0 series has 7 in. collar on all models but also states that the minimum breeching diameter for the WTGO-3 is 5 in. The current setup has the 7 in. vent leaving the boiler and has a reducer to 6 in. with one elbow in the path. The path is in total about 5 feet before reaching the flue. From my understanding and talking to Weil-McLain directly this vent configuration appears acceptable as it is above 5 in. and should not any back pressure scenarios. I am actually using the same configuration that was on the old boiler which was a little larger in BTU and it lasted almost 40 years.

Is something else I am missing? Do I have any hope of changing the inspector's mind?