Joseph Meehan wrote:

I agree with the two answers you already got, but I will add that above
a fireplace is usually not a very good place for a TV. It is a bad working
environment. It also is likely higher than it should be. Generally the
ideal height for a TV is to center the screen the same height as the eyes of
the sitting viewer.

Valid points, though in a great many cases the fireplace is non-working
or a cosmetic gas one.

One thing I would do differently is on the data / LV side. It's unlikely
that you'd want a plain old cable connection to feed a new HD LCD TV on
the wall, so what you want to do is put in a run of large PVC conduit
from behind a cover plate next to the AC outlet above the mantle, and
run it to the nearest or most logical closet location.

Use large conduit such a 3" with gradual sweeps so you will be able to
pull the bulky HDMI connectors through it to the TV. You'll be putting
your cable or satellite box, DVD player, TIVO and audio components in
that closet and controlling them with an infrared repeater setup. Also
prewire speaker wire to that closet from the locations of your speaker /
surround speaker locations in the room.