Look for white staining on the outside bricks (efflorescence), rust on the damper or firebox, or water stains on walls near the chimney. These are early warning signs most homeowners miss.Inside, check for cracked or crumbling mortar, loose bricks, or a musty smell when it’s not in use. If you see daylight through the chimney from your fireplace, that’s a definite problem.The biggest red flag? Water inside your home after storms. By the time you see interior damage, the repair costs have usually tripled.