A TV over the fireplace is one of the most requested mounts and one of the easiest to get wrong. Three things decide whether it works: heat, height and the wall.
Heat
Fireplaces run warm, and heat is hard on a TV. Check the mantel temperature and the clearance after the fire has been going a while; your TV's manual lists the operating range. Where it runs hot, a pull-down mount keeps the screen away from the heat when it is up. A gas insert that stays cool at the mantel is usually fine.
Height
Over a fireplace the TV often ends up too high, so you watch with your neck craned. A pull-down mount solves it by bringing the screen down and forward to eye level when you watch, then tucking it back up. If the mantel is low, a tilt mount can be enough. More in how high to mount a TV.
The wall
A fireplace wall may be solid masonry, or wood framing wrapped in stone veneer, tile or stucco. Masonry needs a hammer drill and anchors rated for the load, set into solid brick or stone and not the mortar joint. Veneer and tile need a diamond bit so the face does not crack. This is no place for drywall anchors.
Wires
Wires can usually be hidden here too, in a framed chase above the firebox or in a clean raceway on solid masonry. See how to hide TV wires.
Want it heat-checked, anchored into the stone and set at a comfortable angle? That is our over-fireplace mounting service.