Clearance from flex liner to concrete mantle?

[JimR1998]

We had a woodburning fireplace that was on the small side and flat against a brick exterior wall. We'd like to put cabinets on either side and don't want the fireplace to be set back the depth of the cabinets, so... we got a gas insert and had the firebox built out about 18" with solid block sides. It now sits on a concrete base 6" off the floor in front of the existing opening. To route the flue pipes, we cut a hole in the existing chimney wall and fed them through.

Is this a totally off-the-wall thing to do? Attached are a few pics of the work in progress. The sides and above the fireplace will be finished with tile. Thoughts so far?

I have a question where the metal flex flue pipes (uninsulated) are exposed going from the fireplace to the chimney. They are only about 2" beneath the concrete mantle. The picture is taken from the top down (see the back of the TV, wires, etc). At first I was just going to cover the gap with durock and tile up the wall, but I'm concerned the mantle will get too hot for TV, wires, etc.

Is that airspace sufficient? Or should I build up a wall of 8" block (unfilled) on the back of the mantle and tile on that? I hate to lose the mantle depth, but if that's the safest way I will go that route.

Nothing inside the enclosure is combustible and there will be no wood anywhere nearby (just durock and tile). I'm mainly concerned about over-heating the mantle and possibly even catching some decoration or some such on fire if it's too hot. I have no idea how it will heat up once it's enclosed.

Chimney guy will advise, but any advice ahead of time is appreciated. Thanks.

 

[DAKSY]

I don't know if it's "off the wall," but you could have bought a gas fireplace instead of an insert & done the install pretty much the same way. You shouldn't have to worry about overheating that mantel shelf. Many of the gas fireplaces & inserts I've installed have had wiring in the cavity with them & never had an issue. You could always add conduit as an extra buffer & run the wiring thru that, if you're really concerned about heat.