I began remodeling my home last month and the only place to put my tv was over my fireplace. Everywhere I read online said don't do it! It's too high, electronics and heat don't mix. Due to the layout of my home I had little choice.
A little more searching and I was able to find some solutions:
1. Heat - Fireplace gets very little use, however if you get a good size mantel, and mount it properly, it will deflect the majority of the heat. I went with a reclaimed 5" deep by 12" wide mantel. I have had no issues or worries about heat.
2. Height of T.V. - I went with Dynamic Mounting. The TV mounts about the mantel, however you can extend the TV below the mantel lowering it over 2' when you want to watch TV
The Dynamic mount does everything as advertised. It lowers the TV to the perfect level while watching the TV when the TV is not in use it quickly goes up into place effortlessly. It is very high quality. I have no concerns having my TV on the mount, it isn't going anywhere.
If you get this mount plan on spending significant time laying out the placement of the mount on your fireplace. If I wasn't totally remodeling my fireplace it might have been easier or completely impossible to use the mount based on the height of my mantel. I spend a couple days going back on forth on the height of the mantel / mount. The higher you place the mount above the mantel the more downward travel you can get.
The instructions could be a little bit better, especially coming to the minor details like the tilt, but if you take and plan everything out it works perfectly. The mount is a little pricey. I got the swiveling mount and it was over 500 dollars. About twice the price of a normal mount, but it is the only mount that I would use over a fireplace. If you right a review / blog / forum post like this one you can also get 100 dollars back like me!
I used concrete anchor bolts with a two part epoxy to mount both the mantel and the Dynamic Mount to the fireplace. I used 7" bolts on the mantel and 3.75" bolts on the mount. I am confident that neither is going anywhere.
I have attached a picture of the finished product. Hopefully this helps someone out there.