Help With Repurposed Insert for Outdoor Fireplace

[Cajundave10]

Hello. I’m building an outdoor patio and picked up a nice sized insert off of Facebook marketplace. I got it framed up and now I am running into issues getting it vented out of the ceiling, specifically finding the appropriate sized pipe to fit the top of the insert.

Here are some facts:
-there is no tag on the fireplace insert so I have not been able to identify the model #
-the old chimney pipe leading into the insert looks like it was cut out. (Angle grinder?)
—the opening coming out of the insert is about 11 1/4” (a size I haven’t been able to find anywhere)
-I need about 10’ to the bottom opening of my chimney

Does anyone have any ideas of how to get this vented out the chimney box appropriately? Any help is appreciated!

 

[begreen]

This is a prefabricated fireplace. An insert goes into an existing fireplace. It's essential to identify the unit so that the installation and flue system are installed according to the manufacturer's tested directions.

 

[Cajundave10]

Yes sir I appreciate the reply. Without any tags/serial numbers etc do you know of any other way to id the prefabricated fireplace so that I can accomplish the proper install?