What the Inland Empire climate quietly does to a chimney
Fontana does not get the freeze-and-thaw winters that wear chimneys out back east, but the Inland Empire has its own slow grind, and it works mostly from the top down. The summer sun bakes a chimney crown and the exposed brick for months at a stretch, driving the masonry through a wide daily temperature swing that opens hairline cracks in the crown and pulls moisture out of the mortar joints until they crumble. By the time the first cool evening makes you want a fire, the cap of the chimney has often spent a whole year quietly deteriorating where nobody can see it from the ground.
Then there is water, which surprises people in a place this dry. When the rain does come to the valley it tends to arrive hard and all at once, and a crown that cracked over the summer or a cap that blew off in a windstorm lets that downpour straight into the flue. Water in a chimney is patient and destructive. It rusts the damper, rots the smoke shelf, breaks down the mortar between flue tiles, and stains the ceiling around the firebox. A chimney that looked perfectly fine in August can be leaking by the first real storm, which is exactly why we push so hard for a look before the burning season rather than after the first wet ceiling.