I'm getting a significant ingress of cold air from the ash dump for my fireplace. I've been puzzled by the dump since I moved in a year and a half ago. It has a brick sized opening, drops down a bit more than a foot, then leads straight back to a metal vent grate on the outside of the chimney, not a cleanout door. There's no easy way to clean the ashes out and not enough space to store ashes for years. Is this set up properly? Is it a vent rather than a dump? Am I OK to stuff ceramic wool down the hole to help seal it up for now? Would it be OK to use the fireplace with the wool in place? The fireplace sees occasional, not regular, use. Thank you! Pictures below.