Replacing with another gas system? Normally, I'd say not but there could be circumstances with the original install.

I have a gas fireplace and the brick right above the fireplace still gets some black soot. But my white mantel (which is closer to the fire opening) does not. But I also have a regular wood burning fireplace in another room and I don't think you will have a problem. You could try it and see if you get any smoke build up and just stop using it as soon as you see black on the bricks. I doubt it could get to your mantel since its so high above the opening. But if you keep it regularly cleaned off, it shouldn't stain your brick. You probably don't retain much heat from vented gas. It goes up the chimney like the wood fire does. But after growing up with real fires, I love my gas fireplace since I don't have to do any work to get a fire. My only beef is that the logs get lots of black soot on them and I have to clean it off at least once a year. It stains the ceramic logs and that can't be removed completely.

Assuming your fireplace draws properly, smoke shouldn't be a problem for the existing wood fireplace - though I can appreciate your concern with the new TV, etc. If you're getting smoke in the room; the fireplace isn't functioning properly: learn about draft at http://www.highschimney.com/articles/chimney-airflow-problems/ As for gas logs, you can use vented logs all day vs a limited burn time for ventless logs. The fire will likely be adjusted to have a yellow flame (vs a blue one like your kitchen stove might) so as to look more like a wood fire. That necessarily means that you will have somewhat incomplete combustion. You'll want CO detectors around because if the exhaust isn't going up the chimney as it should be, you won't get any warning (ie no smoke to choke on). You have to put something in place to insure the fireplace damper can never close 100%- a clipboard clip on the damper plate is often used. Your fireplace has to still work for wood, so don't let anyone suggest you have a smaller liner. This is not something you install yourself; a plumber will run the gas line. I'd suggest getting your log set in a hearth store, where they'll cost more no doubt, but you'll also get knowledgeable people and access to professional installation. And you are right: you do lose heat with an open fireplace. I love the official expression for it: "negative heat gain." Here is a link that might be useful: Types of gas firepaces

Okay I'll post here then. Thanks for the kind words. Disclaimer - no engineer here, only gadgets are the TV and the Wii. We rent movies off of Amazon so no DVD player either. Haha! We use our fireplace all the time. We even use it in the spring when it's sunny but cold and the furnace isn't running as much. It's definitely not just decorative for us. We went back and forth on above the fireplace and beside it also. We finally just went with our initial plan which is what we have. It was hard to decide but I didn't really want the TV above. I also really wanted a hearth which brings the mantle up higher (there is a heat requirement so many inches above the firebox) and that would have made the TV pretty high. We have 9' ceilings. EDIT: Corrected ceiling height to 9'. The cabinets are 19 1/2" deep. The fireplace is 25". When we first moved in we didn't have it mounted yet and it was definitely hard (okay nearly impossible to see the whole screen) to see from the left side of the couch. Most mounts seem to only extend 18" and I knew from just placing the tv at that depth that it was going to be tough to get a full viewing angle at 18". I found this mount: 25" extension articulating mount on amazon and we love it. It pulls forward the 25" and it tilts. Very flexible and it made a huge difference. It now pulls forward about flush with the fireplace when we want it to. We normally keep it in that position but you can push it back to the wall and I don't think it protrudes too much at all. NOTE: For this kind of set up - a 1 arm mount would not work. They do not pull straight out from the wall and with the small clearance we had on either side of the TV we had to have it pull straight out. Mrs Pete I am sure your engineer hubby would be all over that anyhow but I thought I'd mention it. We have a single arm mount on our exercise room tv and I fiddled with that one and realized it wouldn't work for this application. But if you have more clearance you could be fine. I didn't want a huge TV in our living room so I worked around the size he had purchased which I think is a 40"? Something like that. The arches were actually simple to do. We checked out how to do them with drywall but found the ones below and it was so easy. We took measurements and ordered them on line from Archways. They were made to fit and installed by dh in a jiffy. They were reasonably priced too. I think about $30 bucks a piece? Don't quote me though it was too long ago now but I think under $50 for sure? I don't like a lot of nicknacks so I didn't want a lot of shelving for more 'stuff'. The one cabinet on either side suits me fine and it was easier on the budget. I bought cabinets from where we purchased our kitchen cabinets from and DH made a top for it, we painted it to match the trim (which was matched to the cabinets). Built ins can get so pricey. I hope that helps.