Hello everyone! My first post. I have just purchased my first home which has a two flue chimney. I pan on putting an insert into the Fireplace, which is one one flue. The second flue is connected to the oil furnace in the basement, but also has a 'thimble' (?) opening in the kitchen which has since had a metal cap put on it. I assume this would have been for a kitchen stove at one point? I am wondering what the proper way to seal up the opening would be?