Are the details not shown in a section detail on your architectural plans? This isn’t crowd sourceable. Go back to your architect or interior designer to get the details correct. Math errors on things that can burn down your house are worth paying a pro to avoid. A TV above this will result in needing medical attention. Don’t put a TV over a fireplace.

Raise the hearth so that you can sit on it. I'd also make the hearth wrap the fireplace edge like this:

For mantel height, it depends...probably somewhere between 4.5' and 5' height. Your height, the size of the fireplace box, whether you will place a TV above, and perhaps room ceiling height it are factors to consider.

The fire box and view openings are larger than the photo shown.

For height, draw out the wall.

15" hearth, plus firebox. Mantel will have to be a certain distance above fire place opening per install instructions. Top of mantel will be at least 60-66" TV above that.

When you wrap hearth, it impairs cabinets. You can double popout the fireplace or ?

What does the watermark say on the image about "without permission"?

The person that designed the house should be involved.

I'd really consider placing your tv one one side of the fireplace, in place of the bookshelves. That would also allow you to raise the hearth and firebox, and have a taller mantel.

Mark, we designed the house. We are the owner, and the general contractor. We hired a draftsman to draw up a formal blueprint of our vision. It is not important to him whether he be involved in something as trivial as the design of my fireplace; quite frankly, he has more important tasks to occupy his time and gain revenue. The watermark is present on the image from the cabinet designer who is supplying the built-ins. I'm not sure why you commented except to find fault where there is none.

We installed a gas fireplace two years ago and discovered that it could run so hot we needed to install additional tile....so I would not plan to put the TV above, at least until you’ve literally taken the temperature above the running fireplace. The first picture is before the Thasso marble tile and trim pieces were installed above the firebox. We were lucky that it matched our trim color exactly.

Thank you for sharing your experience fissfiss. The unit we bought is mostly for ambience and isn't overly powerful as we do not require it to heat the space. Additionally, it is being installed with a blower to direct the heat away from the wall. I'm glad you found a fix for yours!

What did the designer have in mind?

“Raise the hearth so that you can sit on it.”

I disagree with @Patrick A’s recommendation. I am glad the OP commented in a subsequent post that she won’t be doing that. For others who might look at this thread, the reasons I don’t like a raised hearth for sitting are that no one sits on them because they’re at an uncomfortable height to sit, it’s hard on your back to sit on a ledge like that, and if the fire is going, it’s too hot to sit right against it. A raised hearth large enough for sitting also visually intrudes in the room, can make sofa and chairs harder to place, and makes the room appear less expansive.

No to the raised hearth. They take up usable floor space. I LOVE my TV over the fireplace. It makes for one focal point. As for the height of the mantle, etc. you need to find out the manufacturers specifications in addition to your towns building codes.

Apologies to the OP -- since I have absolutely nothing of value to contribute to this thread -- but I just gotta say, "That is some gorgeous fireplace tile, right there!" to Fiss. :-D Soooo dang pretty. <3 It's making me want a fireplace in Central Texas, where I'd use it maybe three whole times in a single decade, lol.