A chimney chase cover is a cap that seals off the top of a wood framed or brick laid chimney chase. Chimney chase covers are typically made from low grade steel, which will rust over a short period of time. The smallest gap or hole on the chase cover can lead to expensive water damage. If you're noticing a leak or rust stains down the side of your chimney, it is time to replace the rusted cover with a stainless steel cover. Stainless steel covers will never rust, so this will be a one-time fix.
The tools that are needed to successfully replace your chimney chase cover are the following: hammer, flat or Phillips head screw driver, drill, steel cutting drill bit, razor knife, caulk gun, and 1 tube of weather proof silicone. Take a look at this measuring guide to help you measure the chimney chase cover correctly. http://www.rockfordchimneysupply.com/chase-covers.php?holes=1O#chaseform