Fireplace Opening 60"W x 34"D (11" Lintel Depth) x 71"H - Will Exhausto fan even make it draft

[EFW]

I am currently working with a custom builder and architect about this fireplace. The Fireplace is true masonry with a oval clay liner and already built. Beautiful Fireplace but my concern is what ever decorative gas appliance that gets installed even with an exhausto fan, I dont feel it will draft. Attach is a pic. Chimney height is around 25' with no offsets. What would be the best solution on how to know what will work for gas media/gas logset in this fireplace?

 

[bholler]

I am currently working with a custom builder and architect about this fireplace. The Fireplace is true masonry with a oval clay liner and already built. Beautiful Fireplace but my concern is what ever decorative gas appliance that gets installed even with an exhausto fan, I dont feel it will draft. Attach is a pic. Chimney height is around 25' with no offsets. What would be the best solution on how to know what will work for gas media/gas logset in this fireplace?

View attachment 323251

What size is the flue?