Use a smoke guard when your flue is sized too small for the fireplace opening. If you are experiencing smoke roll out from the top of your fireplace, this may be the cure for you. A smoke guard can be used to reduce the height or width of your fireplace opening, making the ratio of the fireplace opening to flue size more compatible. The rule of thumb is that the height should not be more than two thirds of the width.The Smoke Guard is spring loaded and adjusts from 28 1/2 " to 48" and installs easily. Comes in 4" wide and 6" wide sizes in black and 4" wide in brass-plated.