Feeling air in sunroom

Recently moved Into my new dream home. Unfortunately the original builders have went bankrupt and I am now dealing with poor workmanship. In the sunroom there are six windows which are sealed fairly tight. Upon using a lighter to check for air there was normal movement in the flame. When I did the same thing against the ceiling where the shallow pan is installed for a future ceiling fan i felt air immediately when I put my hand against it. How do I remediate the problem before removing all of the sheet rock. Thanks in advance