Energy Saving Insulation for a Fireplace Chimney

Materials Required

• Applying energy-saving insulation around a fireplace chimney requires only two basic materials: metal flashing and silicone caulk. The metal flashing must be at least 14 inches in width and made of 24-gauge sheet steel or aluminum, which provides an effective barrier between the walls of the chimney and the surrounding wood joists and insulation. Silicone caulk must be applied at the joints between the metal flashing and chimney surface to sufficiently suppress air leakage. The caulk must be specifically designed for areas with high or fluctuating temperatures, so ask for high-temperature caulk when making a purchase.

Basic Process

• Building codes require a 1-inch clearance between the chimney and the surrounding wood framing. While this provides some insurance against fires, it also allows warm air to pass from the living space into the attic. Metal flashing must be cut and applied around the base of the chimney so that it covers the gap. Cut the flashing in two pieces and apply one at the base on each side of the chimney so they overlap by 3 inches at the contact site. Secure the flashing with a few beads of high-temperature silicone caulk. Seal the top and bottom edges of the flashing to the chimney structure and the wood joisting around the base using an evenly applied stream of high-temperature caulk. Allow the caulk to set for several hours before using the fireplace.

Maintenance

• Although metal flashing and high-temperature silicone caulk last a long time with minimal degradation, it is best to inspect them each year to ensure they are intact and providing the barrier needed to save energy. Look for bowing or bending in the metal flashing since both can cause a gap to open, which will cause heat loss through seepage. Also, look for tears or gapping along the caulk seam and repair them as soon as possible with more caulk. Issues with bowing metal or gapping caulk indicate that the chimney is becoming too hot and causing the materials to expand or contract with the temperature change. Such an occurrence is likely the cause of an overfed fire that is burning too hot for the structural materials to handle, so keep that in mind the next time you light a fire and avoid applying excessive fuel.

Safety Precautions

• Insulating around a chimney for energy efficiency will improve the overall safety of the unit, but the process does pose certain hazards that must be known if they are to be avoided. First, always allow the chimney to cool completely before attempting to insulate it since there is a chance of burns associated with insulating a hot, active chimney. Also, it is recommended that an insulation damn be built around the chimney before filling in around it with fiber-based insulation. Do this by forming a portion of sheet metal into a tubular shape large enough to encompass the base of the chimney. Bend the metal toward the chimney to create a 1-to-2-inch-wide lip around the top of the tube to hold the exterior portion of the metal away from the structure. Push insulation around the insulation damn to further eliminate potential air loss.