Yep, "masonry" just means anything assembled by masons, eg. stone, brick, concrete, mortar.
Yes, some stoves have clearance issues, even to non-combustibles. I run Blaze King Ashford stoves, and they have a rear clearance requirement, for their thermostat to function properly. I'd be surprised if Englander has anything like that.
Let's get some experts here, to answer your questions:
@stoveguy2esw from England Stove Works
@bholler one of our resident chimney sweep / installer
@BrotherBart 30-NC owner of many years, and his installed half in/out of a fireplace, I think.
@Hogwildz just seems to know a lot about this chit
@Nick Mystic with that fat lady in a small airplane seat tight install
Thank you, thank you!
I am trying to get some control over the process and not just blindly trust the installer (at least give some impression of being able to understand what he is talking about). I am here because I am naturally suspicious, I guess. He claims it is all good to install it inside the fireplace but it is always better to check (I figure) since I could the one stuck with a fire and insurance not covering anything due to an improper installation... Plus, I want the darn thing to actually heat my house hahah