B+ motorhomes

I discovered a strange thing with my stove top exhaust fan. It is not connected to the exterior exhaust vent. Not even a hole cut into the back of the hood to connect to the vent. There are two small slits on each side of the hood but nothing but solid metal on the back wall in front of the exterior vent. I'm thinking this must have been a factory screw up but wonder if anyone can tell me how their exhaust hood is connected to the exterior vent. All the exterior vent does is rattle as we drive down the road.
We just got back from a 7000 mile loop around the west. Great trip. Rig ran great, but oh those Canadian gas prices!