Fireplace construction question
I had a fire in my fireplace on a Sunday afternoon, quit feeding it around 4pm, embers burned out around 7pm or so. I swept the ash into the ash box in the floor of the fireplace around 9. I shut the flue at about 6 the next morning after checking that everything was cooled down. Sometime after midnight Monday night (Tuesday morning I guess), we had some sort of flare up because the house filled with a strong smoke smell, but not enough smoke to set off the smoke/CO detectors. I always noticed our fireplace has a decent draft even when the flue is closed. I was cleaning it out and noticed something I thought was strange. There appears to be a gap between the steel frame surrounding the opening of the fireplace and the stone on the outside of the fireplace. I felt around, and the draft is actually coming from the gap, not the flue door. Is that gap supposed to be there? My concern is that an ember popped up in there and smoldered for the next day or so, creating the smoke (and luckily nothing worse). The other thought on the re-ignition was an ember in the ash box, but everything was cool when I cleaned it out. Anyone have experience with this?
The first picture shows the outside of the fireplace. The stone extend floor to ceiling. The second picture is looking up and out from the inside of the fireplace. It shows the top of the frame and the gap between the frame and the metal "roof" of the inside of the fireplace. I don't know the technical terms so you'll have to forgive me there.