Jack -
We advise against it. The heat and soot are two things that are really bad for TVs, and both are often aimed at televisions that hang over a fireplace.
Of course, it may be that nothing happens, or that you might get years of enjoyment. But we really do recommend against it for those reasons.
Try a different wall, or discuss it further with a contractor or installer who might be able to offer some safeguards or alternatives.
Thanks for your interest in Samsung products.
--Mr. S