I hate to second guess another professional without knowing the whole story, so if you can tell me the exact make & model of the new unit, and maybe post or send me a photo of what you have, I'll be much better equipped to help.

You can post here or send the information to me directly at tom@coastroadonline.com.

Thanks!

Here are a couple of questions that make me wonder what else is happening . . .

Why was the brick facing removed? Most of the time we install stone right over the brick.

Why is the gas insert "significantly smaller"? We usually are able to get pretty close with the fireplace opening size, especially if we use an "inside fit" surround, like shown below.

Is the firebox itself masonry, or it a manfactured heatform or firebox? In a situation like this with a manufactured firebox, we usually tear out the old firebox and start with a new fireplace, where there are a lot more options, especially if you're already planning to reface it.

What kind of stone are you installing? If you are installing an insert with an overlap face, it is a challenge to make it fit nicely against stone with any variation in depth, leaving big gaps around the sides and top. I'd usually suggest an inside fit surround on something like that. In either of those cases, the stone SHOULD be installed first, but the other questions above make me wonder.
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Thanks for your replies. I removed the brick face because as you can see, it took up half of the fairly small family room. It is quite a tall opening, 36h x 37w. It is full masonry and I was wanting to put stacked stone veneer panels and a mantel on the face. The insert I bought is a Heat & Glo Escape-135FB. Thanks!

And I won't be putting a hearth in. I want to run it straight to the floor to leave more space in the room.

Thanks for the info, Tish.

What kind of shelf are you using? Do you have a picture?

Are you running the stone up to the ceiling?

Which face are you using on the Escape insert? The Chateau, Halston or Galleria? The Vision, Glass or Firescreen front?

There are some tricks to closing up the fireplace opening a little that might be worth considering . . .