The back wall is steel studs and sheetrock. This was framed first. Then the fireplace unit was set in place with it's flue. It is a manufactured gas fireplace with a glass face. Heat is not an issue. The metal fireplace surround was then set. I was not there when they installed it but it was made, i believe, in four sections and I believe it was self supporting w/o any additional framing or skeleton. The installer/fabricator was Matt Deschler with Formed Objects. They do great work. You may be able to het more detailed info from him. http://www.formedobjects.com/