On Feb 23, 12:07*pm, raymcgill wrote:
The problem is that a coal fireplace necks down into a slit right
above the firebox. So I have a space 18 long and 0.75 inch tall.
Needless to say, the 4" proper vent pipe isn't going to fit...
Any suggestions?

A good sheet metal shop can make a transition piece for this quit
easily. Since the areas are nearly equal it should be a breeze. It
will wind up looking something like a wide shop vac floor nozzle. HTH

Joe