There are several methods to clean fireplace brick, but one of the easiest, and most effective is to use oven cleaner. Oven cleaner is designed to remove scorched and baked-on debris. Do test a small spot before using on the entire brick surface. Be sure there is no fire in the fireplace when spraying the oven cleaner as the can is under pressure. Spray the oven cleaner on the brick and allow it to sit on the brick surface the amount of time suggested by the cleaner's label when employed for oven use, then wipe away with a heavy cloth.