How do you clean soot off of a fireplace?

If your chimney is in good order, the built-up grime should not be too difficult to remove. It can be done with a diluted household cleaner and an old toothbrush or scrub brush. The only issue which might arise would be if there was very heavy creosote build-up inside the flue itself. At this point, it may require further attention from a professional chimney sweep to ensure that the firebox area remains safe for use after cleaning has been completed.