Lack of cleaning and regular maintenance can lead to soot buildup in your furnace and furnace break downs, including the expulsion of black soot through the air vent ducts which can cover your home in a black dust.
Sometimes, the expulsion of soot can be due to a faulty exhaust system (flue) or improper venting. Other times it can be caused by a fuel leak or faulty parts, such as the fuel nozzle/valve in the combustion chamber leaking fuel. It’s best to hire a professional and licensed HVAC technician to inspect and repair the furnace. However, you can do some basic maintenance and cleanup yourself. Here are the basic guidelines for a DIY furnace cleanup and some repair tips: