A spark arresting chimney rain cap installation is a smart move for several reasons. These caps are tight-fitting metal chimney caps that reduce 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. Let’s go over these advantages from my vantage point, that of having cleaned several thousand chimneys and that of having repaired several hundred chimneys in my career.
Getting the obvious out of the way first- water and animals.
Water can break a chimney apart. Specifically, freezing water can break a chimney apart over time. This phenomenon is a form of “frost wedging”. Think of the ice tray in your freezer. The ideal scene for a chimney during freezing temperatures is that it is dry on the inside and that moisture cannot penetrate the outside. Siloxane can be applied to the exterior of the chimney to waterproof it. Siloxane allows moisture to breathe out of the chimney and will not allow moisture to penetrate it.
Water can also rust out metal chimney dampers, causing a spendy fireplace damper repair. Chimney swifts, which are a federally protected species, frequently have their babies in the deep chambers of fireplace chimneys. These birds cannot be removed while the babies are growing strong enough to leave the chimney. As a matter of fact, you have to wait until they leave before you can put a rain cap on the chimney that would prevent them from coming and going.
When do chimney swifts leave
They start leaving around October-November. See the video below of a chimney full of chirping baby swifts:
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. And then there is this regarding raccoons:
”Because raccoons are the primary host of Baylisascaris procyanis, a roundworm that can harm people, and the roundworm eggs may be present in raccoon feces, their latrines should be removed and cleaned up whenever they might pose a health hazard. This the task requires extreme caution.” (Humanesociety.org)
Raccoons in the attic or chimney are bad news. We leave it to the pros to remove them.
If you have a fireplace damper that needs to be replaced, you can have a top-closing damper/rain cap combination installed on top of the chimney to replace the worn or missing fireplace damper.
Multi-flue chimneys: points to consider when installing a chimney rain cap
One potential problem with a multi-flue chimney is smoke coming out of one flue and being pulled down another flue, thus smoking out the room that is pulling the smoke down. This does not always happen, but when it does the problem is that all of the flue tiles on top of the chimney are level with each other. One way to handle this problem is to have the various flue tiles staggered in height so that they are not even with each other.
Mass-produced rain caps can be installed (usually….) on the individual flue tiles. Another option, that provides a more attractive appearance is to have a multi-flue rain cap custom made that has dividers within the cap. The dividers solve the problem of equilateral smoke transfer from one flue down another.
You may need to have some repairs made to your chimney before a chimney cap can be installed. Rain caps can be blown off if their foundation is weak. I have seen a rain cap installed on a flue tile that was not cemented properly to the top of the chimney. A windstorm hit and the rain cap (remaining screwed to the flue tile) and flue tile as one unit blew off of the top of the chimney.