may i put an hdtv over a fireplace?

No. Unless you have bleachers in your living room. If not you will have stiff neck, everytime you sit down. As far as heat goes, how many days in a year is there a need for fire, unless you live in Alaska. Isolation material behind and under the flat screen should take care of that.

I've got better idea:
It's OK to me to hang it above the fireplace if you're not going to use it as a fireplace. Instead you could use it as component compartment.
But MAKE SURE that EVERYBODY knows that this isn't a fire place anymore!!!!!!!

Pretty good rcprince.
I think it would be OK with a gas stove as long as there are no great heat problems. I would have it built into a sealed enclosure though for aesthetics, and to keep out smoke and lessen the heat. You could also have this enclosure somehow cover the screen when not in use.

Maybe you could just project a live video feed - people will think it's a mirror.

Why sure you can. Don't listen to the above posters. They are just jealous cause they never thought of it before. I bet most of them are hanging their's above the fireplace as I type, just trying to be the first to post how they love the way their new flatscreen looks over the fireplace. Well they may as well forget it, cause I was the first. I wasn't going to let anyone else know about it cause I wanted to be the only one to have such a novelty. Yep, got mine hung up on the wall over the fireplace with thumb tacks, the center speaker on the hearth and the fronts on the mantle. For rears I mounted some good in wall speakers in the lampshades on each side of the couch. pretty nifty huh?
Now if you didn't catch that bit of sarcasm the answer is No No No

Good question; one I've thought about for my room a number of times. If I could put my screen over the fireplace, it would solve a lot of problems, like better placement for my speakers on either side of the fireplace, and like better seating options, where the seats can face the fireplace and the TV at the same time.

Check to see how hot the wall gets. Some chimneys are well-insulated and don't heat up the wall over the fireplace significantly. Alternatively, you could put some kind of thermal insulation between the wall and the screen. The challenge would be to make the insulation effective but still aesthetically acceptable, e.g., make it look like a picture frame.

Make sure you have appropriate drafting whenever you have a fire. (I assume you might want a fire from time to time, although you never said so.) Alternatively, you might have a mantelpiece that effectively shields your wall from carbon fouling. Check the wall now and see if there are significant deposits. If so, consider cheap ways to make the mantelpiece deeper, like putting a wide board across the top. Experiment and see if this stops the carbon deposits.

You need to feel good about the screen height. We have all seen the magazine ads with the screen over the fireplace. Unless you can sit far enough away, you will be looking upwards at the screen. This would be like always being forced to take a front row seat at a theater -- your own! Personally, I like looking slightly downward at a screen, and my old direct view that sits on its dedicated pedestal is perfect for this. Good luck!

Tim, sometimes it's about a bailey's and coffee, snuggling up with someone you love, the cat curled up in your lap - watching a movie... :) aj

aj-now I realize we are a little different but romance and TV don't go together in my book ;) the sofa, the fireplace and maybe some small monitors playing light back ground music.
Tim

I don't know about your fireplace, but mine gets soot above it - no matter how much I clean.... I would NEVER risk putting something over it.
Too bad, it would be the ultimate, eh? Sofa facing the fireplace AND tv....
aj

ARE you for real or just kidding.Never in my lifetime especially at the price they go for.Maybe your loaded I tell you what if you want to put it over the fireplace buy me one because I can see you buying a new one every year.

although I would agree that the programning on TV these days is crap, you have to admit that an HDTV signal is really pretty amazing. I would say it is as good if not better then DVD. And it certainly blows "normal" sat. images away.

Judd MacRae

Two considerations: Excess Heat & Carbon Fouling.

You probably would need to build an "improper fire" ie hotter than it should be, and measure how much heat is in the area you want to mount the unit.

The issue with carbon fouling or other pollution aspects will occur when the fireplace doesn't draft properly. Very importnat to have excess makeup air to help the chimne draft properly. Weather conditions can still cause problems however. Even with a gas fireplace you will be dealing with trace amounts of sulfuric acid pollution. Thats why gas appliances require stainless steel or galvanized steel liners.

While the location may be aesthetically interesting, I think from a long term viewpoint this is an inappropriate location for any electronics.

Considering what I've seen on TV these days, how about IN the fireplace??? Come on now, you were waiting for that one, weren't you?