Boiler Flue Vent Connection Question

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?

I have no idea about your actual code but up here in BC we are allowed to reduce (when acceptable by the mfg.) right at the exhaust connection on the appliance. In other words the 7x6 reduce would have to be screwed onto the appliance it served.

Do you have a picture?

it should be @ the chimney or @ boiler and not on the run so have a thimble in the chimney then ur reducer / increaser then ur flue pipe but each state town's has they own rules.