Related Clues:

• Chimney substance
• A pollutant
• Chimney pollutant
• 29-Down buildup
• Film in a flue
• Laundry woe at the Claus home?
• Dirty coat in a chimney
• Flue grime
• Air polluter
• Fossil fuel residue
• It may be caught in the flue
• Dirty film?
• It turns Santa's suit black
• Smokestack buildup
• Diesel by-product