The answer to 'how to clean furnace' is to regularly clean and maintain your furnace to ensure it runs efficiently and safely. This typically involves cleaning or replacing the air filter, clearing any debris or dust buildup, and inspecting the key components like the blower motor and heat exchanger.
You should clean your furnace at least once a year, preferably before the start of the heating season. This will help extend the life of your furnace and improve its performance. Be sure to turn off power to the unit and follow all safety precautions when performing any maintenance.