In order for an electric fireplace insert to be installed in an existing fireplace, that existing fireplace must be removed of all existing fireplace apparatus.
This is because an electric fireplace insert sits partially within the firebox of the existing fireplace.
The existing fireplace should therefore be cleared out to make it ready for the new insert.
As an example, we’re removed an old gas fireplace insert from our kitchen fireplace (more about that removal here) that didn’t work to allow us install this electric fireplace insert.
We’ve since tidied and cleaned up this fireplace ready for installing our electric insert.