This information is from the Panasonic site ….

3. Can I mount the TV over my fireplace? As long as the plasma TV will not be exposed to smoke or excessive heat, it should be fine. First, take a thermometer and tape it to the area directly above your fireplace — where the plasma will be. Then build a nice fire and monitor the thermometer for the next hour or so. If the temperature is above 104 degrees F, then the area is too hot for your plasma to be operating. Of course, you could choose to keep your plasma turned off while a fire is burning. In the end, please use common sense. If the area above your fireplace is too warm or exposed to smoke, you probably want to put your plasma TV somewhere else.