Well there's a trap door at the back we dump ashes into -- goes all the way down to basement. So, not sure.
Discussion
it's almost certainly an air intake then, and is probably clogged, so if you can open it and clean it, your fire will burn hotter and more cleanly
Thanks #plebs! Crowdsourced answers. Love it.
Our fireplace has a built-in metal firebox with air ducts surrounding it. As the air in the surrounding chambers is heated, it rises by convection, drawing cool air in from two entry vents at floor level and allowing that air to flow out through a vent just above and under the mantle.😁
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i'm a born hacker... if there is a button, a lever, a slide, i tweak it and see what happens
