Planning an addition on my house. Wife want's a fireplace. Ideally I would like a dual-fuel propane and wood if that's even possible. I really want the fireplace within the confines of the new walls and not have it bump out but my concrete guy says he needs 40+ of depth for a site-built fireplace. I'm finding slim-line fireplace kits on line that need less than 30". Looking for some experiences with the slim-line high-efficiency fireplace kits. Am I better off with a kit or trust the concrete/mason guy to site-build something that will actually flow well?

Have you considered a stove? I don't have a recommendation for the dual-fuel request, but the stove would negate needing to bump out a wall.

This. We took out an enclosed gas fireplace in our house and replaced it with a wood burning stove from an outfit out of Canada. Minimal clearances around the unit and pipe as the insulate it all. Draws are from the outside and of course vented outside. Uses a fan to blow the hot air Can be ducted in to central air if desired.

Or just a stand alone as pictured.

Stand-alone is the way to go in nearly all situations. Nearly zero clearance and it's easy to poke a hole in the wall or roof for it. No framing. No masonry. Easy to service. Our place has a traditional fireplace and a couple of old wood burning stoves in some rooms from the 1800s. During the freeze, when we lost power for a week, those stoves are what kept the house or rooms at 80 degrees.

Yes. 80 degrees. I was sweating while it was 13 outside. They are superiors heat producers. On a traditional all of it goes up the chimney.

Yeah. I didn't mention it in my original post, but the stoves don't play around when it comes to producing heat. Don't start running it just so you can look at a pretty fire. A legit cast-iron one is what a Vikings dreams are made of.

Never going back to wood, even with all the free wood on our property Soooo if she likes to gather, ash-dump, guard against termites/snakes and do it all when freezing outside .... forgetaboutit and get a huge propane tank, then a stand alone/equal DirectVent fireplace.

A properly working wood stove / heater produces little ash. Hell, mine turns a 1/4 cord of wood into ash that barely fills a 5 gallon bucket.

I had a talk with the "boss" last night. She wants the ambiance more than the heat. Given that and the limited space I'm looking at a gas (propane actually) fireplace kit from Heatilator. It can be vented out the back instead of requiring a chimney. We can still do a rock faade on the inside to get the look she wants. It also has a battery backup so it can operate during a power outage to provide heat when the furnace can't operate. Anyone have a review of Heatilator or other built-in gas fireplace? This is the one I'm considering.

https://www.heatilator.com/fireplaces/gas/reveal-gas-fireplace

BINGO!