I recently had the flue to our old oil boiler capped and sealed on the inside of the house. It was a short horizontal clay thimble that connected to the vertical run. I plan to leave the rain mesh cap on the top for ventilation in case moisture somehow gets in. I assume before, the heat from the flue took care of any potential moisture build up. Now that it’s only open at the top, and no heat is going through it, I’m hoping I didn’t create a problem. Any thoughts? The chimney is pretty waterproof, just had the mortar done and Siloxane on it a few years ago.