where to mount ductwork?

[bison1973]

I had some ductwork made to mount to the back of my firebox below the grates. It runs almost the width of firebox. Question is where do I attach it? Right below the gates, in the middle, or at the bottom near the floor?

[RileySugarbush]

Anywhere below the grates will work fine. The air has no choice but to go up through the fire. I noticed on mine that it had a little more flow up by the door so I put a firebrick in front of the entrance to break up the flow some.