The majority of fireplaces are more than likely going to be built with brick surrounds, often on an external wall, with the chimney being the intended position for the LCD TV to be mounted.

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Given the weight of an LCD TV and its attached wall mount, it is likely to be trickier to mount a TV to a brick wall than it is an interior stud wall.
As such, some heavy duty hardware is required – namely a hammer drill and suitable masonry bit for your wall mount. The mount must be securely anchored to your brick wall in order for the LCD TV to remain in position, with some calculation done beforehand to ensure that you’re drilling into the centre of the bricks and not the edges, which will result in some cracking, even behind a layer of plaster. Of course, you could opt to remove the plaster, then with the mount successfully anchored to the wall, re-plaster the area behind the TV.
Once the wall mount is successfully attached the wall, it is simply a case of fitting the TV mount and sliding the two sections together above your fireplace. Don’t worry about heat or soot - your display is protected, just as you are.
Just enjoy your LCD TV!