I think the breeze is moving exhaust from the vent termination to the cat door. being under the over hang doesn't help. I'd extend the vertical section up, maybe throw in a 45, get the termination cap out from under the overhang and above the level of the cat door, hot air rises you know.
I'd also want the floor protection under the stove to extend at least a foot out in
front of the stove. Maybe codes & manufacturer only require or suggest 6" but that's not a limit. The under stove protects when the stove is running, but there are times when someone will have a door open and hot particles can sometimes just find their way out.
I'd have the floor behind the stove under the exhaust outlet all the way into the corner covered as well as the 6 or more inches to the sides. Could be a wooden base with thin pavers & mortar under the iron you have ... or instead of same.
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