I came across this Goodman gas furnace hanging flush against the Dow styrofoam sheathing in an attic. I called Goodman to ask about the required clearance since the manual was not laying around. They told me manufacturer required 4" minimum clearance on all sides, but in TN it was 12", since they are based there I guess.
I wrote it as deficient, but just curious about if it was mounted against any other type of wall sheathing if there should be more clearance than 4". Anyone ever come across this type of install?