>If the walls are built to fire-code, and a proper fire-rated door is used, it shouldn’t be an issue >even if the room opened into the garage. Sorry, I believe that's wrong. Under the building code, which refers back to NFPA 54, "any room" that is accesable only thru a garage also needs to have the source of ignition 18" above the floor. So if NFPA 211 will not allow a solid fuel boiler in a garage, building a room with a door that opened directly into the garage IMHO wouldn't fly. The issue being the possibility of igniting gas fumes & vapors.