How do I Insulate Walls Around a Chimney?

Walls that adjoin chimneys are almost always drafty and mostly need to have cracks and air holes sealed with some type of insulation. Whether you use spray foam insulation, fiberglass or even rigid insulation, several methods are available to seal these breezy gaps. The good news is the average do-it-yourselfer can complete this project in one to two hours, depending on the size of the project.

Things You'll Need

• Spray foam insulation
• Fiberglass batt insulation
• Rigid foam insulation
• Measuring stick
• Caulk

Instructions

1. Remove any trim from around the fireplace surround. The walls that meet the fireplace and chimney will often be fitted with trim to close off any gaps between the masonry and wood. Removal of this trim will allow you to properly assess and insulate the gaps.

2. Remove old insulation and debris from the gaps. Any debris or old insulation will prevent proper installation of new insulation. Wear a dust mask to prevent inhalation of dust particles that may be harmful to your lungs.

3. Fill gaps less than two inches with spray foam insulation. You can purchase 16 oz. cans at a hardware store. Use maximum expansion foam so the gaps will fully seal. After spraying the foam directly into the gaps between the wall and chimney, wait an hour and trim away the excess that has expanded outside the wall.

4. Fill gaps two to four inches with rigid foam insulation. You can purchase this insulation at your local hardware store, as well. It comes in 4-by-8-foot sheets that are 1/2-inch thick. Use a razor knife to cut smaller pieces down and stuff them into the gaps. You may need to insert several cut pieces into a gap to fill the gap completely.

5. Fill gaps larger than four inches with fiberglass insulation purchased in rolls at any hardware store. Use a yard stick to poke insulation into these gaps. Stuff the insulation into the gaps until the space has been filled. The insulation has a paper side and a pink fiberglass side, either side will be OK to stuff in first.

6. Replace the trim around the fireplace and chimney. Use a trim nailer or glue the trim around the fireplace. Caulk all cracks around the trim so to prevent any air from penetrating the trim.

Tips & Warnings

• Always wear protective clothing, such as long sleeves, a dust mask and eye goggles, when handling fiberglass insulation.

• Make sure no insulation is within two inches of any chimney pipe that may carry heat.

References

• "Insulating, Sealing & Ventilating Your House;" William Perkins Spense; 2006