Related Clues:

• Combustion byproduct
• Chimney output
• Grayish
• Flue buildup
• Santa soiler
• Wood for a 61-Down
• Hot flick?
• 'Red' or 'white' tree
• Grate stuff
• Fire sign
• Olive kin
• Smog contributor
• Pipe sullier
• Combustion residue
• Tough wood