Fireplaces are much more efficient and safe when covered with a set of glass doors. The solid surface will radiate heat and at the same time allow you to enjoy the appearance of dancing flames, all while preventing room heat from escaping up the chimney. You will need to apply insulation around the frame of the glass doors to stop the airflow between the irregularities of the frame and the masonry of the fireplace opening. From time to time, you will need to replace that insulation.
Things You'll Need
Fireplace self-adhesive insulation strips
Let any remaining fire burn out in the fireplace so that the doors are room temperature before you attempt to work with them. Do not do this job with a fire burning to avoid injury or fire.
Loosen the lintel clamps holding the glass door framework in position against the fireplace. Have someone hold the frame while you unscrew the clamps to prevent the frame from falling onto the floor once you have it loosened.
Pull away the old insulation that is stuck to the back of the frame or against the fireplace. Wear gloves to keep fiberglass splinters from getting under your skin. Scrape off any small amounts of adhesive that remain.
Press sections of self-adhesive fireplace insulation stripping around the frame.
Hold the frame back into position with the lintel clamps and tighten to position the frame back over the fireplace opening. Screw the clamps until the insulation is sandwiched between the frame and the masonry of the fireplace.
This procedure can also be followed for replacing insulation around doors of wood-burning stoves.