Venting a pellet stove to a coal fireplace

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?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

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
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.