Sveral things to consider....some folks really frown on a TV over a working fireplace, inside and outside the AV industry, but like anything else in life, it all depends. Appears you have a gas fed fireplace, is that correct? If so, is it a vented/heat "expelling" fireplace, or simply a non-vented ambient style? If it's either gas or wood burning, and it does expel heat ( other than radiant heat ), that poses a potential issue especially if the TV is a plasma. LCD/LED not so much. You need to see how much heat travels up the wall in front as that will directly impact the TV. Not that it's going to spontaneously combust while watching a Seinfeld re-run one night, rather excess heat to the TV can shorten it's life ( why plasmas are so sensitive, since they put off their own amount of heat ) due to cooling issues.
Another is viewing angle, even with the screen angled towards the seating position, your neck is going to rebel after a while. Using an extreme analogy, think how your neck felt the first time you had to sit in one of the front rows at a movie theater.......
Lastly is proper mounting. If it's a gas fired hearth, originally designed as such, I imagine the wall structure is standard framing with 2Xs. If gas converted, or a wood burning brick covered with furring strips and drywall, you'll need to find out how the drywall is fastened. A 40" wont be that heavy, unless it's a plasma, as those are the heaviest of formats.
Another is viewing angle, even with the screen angled towards the seating position, your neck is going to rebel after a while. Using an extreme analogy, think how your neck felt the first time you had to sit in one of the front rows at a movie theater.......
Lastly is proper mounting. If it's a gas fired hearth, originally designed as such, I imagine the wall structure is standard framing with 2Xs. If gas converted, or a wood burning brick covered with furring strips and drywall, you'll need to find out how the drywall is fastened. A 40" wont be that heavy, unless it's a plasma, as those are the heaviest of formats.