A spark arrestor is a tight-fitting metal chimney cap that reduces spark output into the environment. They are made of galvanized steel, stainless steel, copper, etc. This year I have received more requests than any of the previous 20 years for spark arrestors. The exact term used was "spark arrestor." This tells me that people are concerned more than ever about preventing wildfires.
A homeowner gets the additional benefit of keeping the inside of the chimney flue dry and keeping animals from nesting in the chimney. Another benefit is that the damper does not rust (spendy repair bill when I have to replace a damper…) The list of dead animals I have pulled out of a chimney with no rain cap is birds, squirrels and a duck! Homeowners complained about the odor. Even though I have a vested interest in selling the idea of purchasing a spark arrestor, it does make good sense and is a wise use of your money. Having completed that pitch, Happy Labor Day!