What do you mean by "not utilizing the space"? Do you think the insert is too small? It heats 1,000 sq ft. Is that not enough? I have a Regency F1100 freestanding stove and I use it as my main heat source here in Vermont. Bigger is NOT better when it comes to wood heat.

Look into cultured stone

Depends on the type of gas fireplace. If it is a direct vent, you cannot remove the glass, but you can hide it with a decorative front. Please post some pictures of the fireplace so we can see what you have. If you can find the brand and model number, post that too.

Does anyone have any idea where we might be able to find something like this in the NYC area? We have 2 fireplaces in our 1905 Victorian era wood frame house and trying to bring the fireplaces back to their original glory. The first attached photo (excuse the mess!) is of one we have that is in great condition. The second photo is of the one we need to replace. The old owners of the home removed the center piece and created a vent for a wood stove fireplace (sigh). We plan to search local salvage yards, etc, but is anyone aware of any websites where we might be able to source something like this, even if just a replica?