I have a furnace and boiler (both gas) in one closet whose floor has a vent at the bottom and the top is completely open to the attic. The attic has blown in cellulose insulation and it falls in this closet when there is work done there. Is this normal or can I partly cover the top with drywall leaving some opening? Any advise on this is highly appreciated. 1600 sq ft house The boiler and furnace exhaust are channeled into the chimney.