Plasma TV over the Fireplace? I am here to dispel the rumor that you cannot put a flat screen TV over a fireplace but you do need to take a few precautions. First, understand that flat screens operate safely in a temperature range of 32-100 degrees so you need to find out how hot it gets above your fireplace. Simply tape a thermometer to the wall at the lowest point where the screen would hang and get a rip-roaring fire going. Since the TV sticks out 3-4 inches you might want to mount the thermometer out 3-4 inches to simulate where the actual screen would be. After a while check to see the temperature readings. If it is at or above 100 degrees then it is too hot to have a fire and turn on the TV together, but as long as you don't try to do both you will be fine. The TV can be stored (or hung on the wall without a fire) at about 120 degrees without damaging the display, but I doubt many people keep their house at 120. Sometimes it's a matter of moving the TV up a little. Every mantel is different and if it sticks out far it might deflect heat much better than a puny mantel. Heat can also radiate out from the chimney so it's important to let the fire burn for a while, maybe an hour or more to get an accurate reading. TVs are designed to operate at a low-medium ambient temperature so manufactures will void the warranty if the TV was operated under high ambient temperatures for an extended period of time. On the flip side, if the TV gets too cold them the performance will start to degrade. I guess the moral of the story is don't bring the TV outside on Superbowl Sunday if you live up Nawth.
Proper air flow is important so recessing the TV in the wall is not a great idea and when you want to upgrade from a 42" to the new 50" model you will have to rip the wall apart and enlarge the opening. Having the TV up so high puts it well above the optimum viewing height so you will need a good sturdy mounting bracket which can be tilted. If you have ever been in a sports bar you know what I mean as all the TVs seem to be staring down at you from the ceiling. Although it's fine for a while, watching a TV with your head tilted back might cause some neck fatigue so be prepared for this possibility. Optimally you want the center of the screen at eye level when seated in your comfy couch or Lazyboy. On the flip side, maybe one way to get the children to watch less TV is to make it less comfortable by placing it high on the wall.