Share 'Attempting to identify fireplace outside air intake'

Wood burning fireplace on 13 year old home in Wisconsin. Exterior wall with cantilevered chase. During blower door test I found noticeable air leakage to the inside from above the metal firebox. Would naturally suspect air leakage from the top and back of the chase. However, there are 2 air intakes on the chase - one is for outside air to the firebox as expected. The other one seems to be just an…