Click on the diagram for the full size image. I'm reading 24" to the mantel and top trim in the Clydesdale manual. I think the shield would need to project from the surround 1" past where 24" hits the mantel molding.
The Jotul C450 manual is located here: (broken link removed to http://www.jotul.com/en-us/wwwjotulus/Main-menu/Technical-documentation/)
Thanks for checking that out! So, I just checked, that would mean the heat shield would have to protrude from the surround about 5 1/2". That's gotta be kinda ugly...not that there's much choice. The clearances on the Hampton are better, but...
Actually, where did you see the 24" number...I keep seeing 27". That 3" would make a big difference considering the geometry of my mantle.
(broken link removed to http://www.hearthstonestoves.com/wood-stoves/stove-details?product_id=16)is where I saw 27", under documents, schematic.