Just to be more specific, this is called the fresh air heater because it draws it's air from outside through those louvers. The other knd of heater does not attach there and recirculates air from inside the cab through the heater core.

1951 GMC 1 Ton Flatbed -- It is finally on the road and what a great time I have driving it!
1951 1 Ton Completed

My Chevy Master 4 Door is on the Road!