Fixing up the chimney flue: Your old chimney may appear solid on the outside, while it’s crumbling on the inside, putting your home and family at risk of fire.

If your masonry chimney is more than 10 years old, it’s probably due for an inspection. Some old chimneys aren’t lined and the mortar used between bricks or stones can break down from exposure to heat, smoke, gasses, and emissions from burning wood or appliances. Even the clay liners used in masonry chimneys can crack and fall apart over time. Any of these factors can lead to a dangerous and extremely destructive chimney fire.

Looking for trouble with your chimney flue: Cracks on the outside indicate chimney deterioration, but troubles usually hide inside. Watch for falling bits of mortar, brick, and sand when you open the damper. Use a powerful flashlight to peer inside from above or below, and push on the mortar with a knife to see if it gives. Better yet, call in a professional. A chimney sweep or local fireplace or wood-burning stove dealer can give a prognosis; some even use special video cameras on fiberglass rods to get the whole picture.

Lining up a new chimney flue liner: An ailing chimney needs a new liner, perhaps one made of lightweight insulating concrete that a professional pours into place from above. Another option is a stainless steel liner.