Indeed, you can personally undertake the task of furnace cleaning, provided you adhere to some essential steps. Power down the furnace by shutting off both the electrical supply and the fuel line. Take off the access panels to permit inspection of the interior workings. With a vacuum that has a long, narrow nozzle attachment, you can gussy up the blower, motor, and any other readily accessible parts. If there are any filters, clean or replace them. Again, if you have any flame sensors, clean them too, and check all belts and ducts for any top secret signage. Actually, if you find anything inside your furnace that looks like it needs attention, hire a pro. On the other hand, if you have a Union Furnace, you can probably fix that by yourself.