24 inch thick concrete hearth

I'd frame it and put down subflooring, then do what you want/need to do for a hearth above that. As a related example, I'll attach pics of the our old "conversation pit" and what we did with it...framed, floored, then built a masonry hearth. Rick

The old setup was the original and was there when we bought the house...a standard old masonry fireplace down in an inglenook. I never lit a fire in it. We had tenants in the house for a year or so before we could come out from Virginia and move in, he reported that he used the old fireplace, as well as the old Lopi M530 freestanding, which was across the room from this fireplace, and still had $300.00/mo electricity bills for the central electric forced air furnace during wintertime. I think he really didn't know what the heck he was doing (but he also had two teenage daughters, so I can't be too rough on him). Anyway, among the first things we did after moving in was to have the old fireplace sealed up, the floor framed, and the brick hearth built, then a new Lopi Liberty freestanding woodstove installed. I never burned in the old Lopi again after I got the Liberty up and running, and the old one's long gone now, but even the old Lopi was about all we needed. I never burned any wood in the old masonry fireplace because I didn't want to waste wood. So...to answer your question (sorry)...you're looking at pictures of an apple and an orange. The old was basically an open masonry fireplace, the new is a freestanding woodstove with a blower kit. We're heating a 2500 sq ft two-level home (upstairs is lofted, so it gets right toasty up there), and only very rarely last winter did we turn on the electric heat. The house is currently undergoing some major renovations which include a whole bunch more insulation and tightening up of everything, so I expect to be even more comfortable in winters to come. Rick

Yeah, BG, he likes it so much I have to walk around him to tend the stove. The change in the usefulness/dynamics of our greatroom by getting rid of that stupid pit with its railing around it were dramatic. We're very happy we did it. Rick

RobertVL" date="1221335598"]24 inch thick concrete hearth(hearth size is 5.75'x5.75')
I have two options , either install a 2x10 floor , put plywood and then sheet rock and then finally a layer of bricks
But I really think my best option is to fill the hole with concrete

Click to expand...

Don't fill the hole with concrete. Stuff is spensive...were it me, assuming the doors are gone, frame in the square and use block or a "hillbilly header" to take up the space between the floor and the top of those stairs. Within that square, i'd run T-Irons across to support a course of brick/block and finish it off however you'd like. I wouldn't fill that entire space with concrete unless I was Italian or had connections. That's how I did my hearth and it's fireproof, cost effective and won't take 40 years to completely dry.

More than likely your existing foundation is not adequate to support the weight of that much concrete. I would definitely frame it in with 2X material on 16" centers, may even go to 12" centers. Cover it with one layer of 3/4" plywood and atleast two layers of durock. Then you can tile, brick, or whatever you want. But concrete would be my last choice.

aussieblake