Your furnace should be cleaned every year by a trained professional. The nozzle and oil filter should be changed as well. The smoke pipe should be removed and brushed out. The chimney should be inspected to make sure there are no blockages and that it is up to code. The heat exchanger should be inspected to ensure there are no holes.After the cleaning is finished the appliance should be fired up and an efficiency test should be carried out to make any adjustments to ensure the highest efficiency is reached.Furnace Cleaning- $100 (nozzle and filter included).