The next time you're in a store that displays flat screen TV's, either plasma or LCD, place your hand just behind the screen at the top edge. There will be a long row of vents incorporated into the set. You'll be surprised at the amount of heat coming out of them. The salesperson should certainly tell you that, although both types have improved greatly, the most common failure of either is due to heat. Any addtional heat, such as from your fireplace, can't do it any good and may cause premature failure, which is extremely expensive, since most of them can't be repaired but must be replaced...