As a general rule, you should never consider smelly air coming from your furnace and out of your ducts to be nothing to worry about. Some smells can be completely harmless, but more often than not, if your furnace is producing smelly air in your home, it is an indicator of a problem. As such, you need to be able to deduce what might be happening and take the right action.
Everything gathers dust over time. If you are starting your furnace for the first time in the season, it will likely have a dusty smell to the air for the first few days. You can combat the smell by running the furnace with the windows open for an hour or two just to get all that dust out of the system.
Metallic or Burning Smell
This is definitely more worrisome. Often if you smell metal or burning, you have something burning in a place it is not supposed to be. If your air filter is very dirty, it can produce this smell, but you still need to have some investigation done. What you really need to worry about is faulty wiring or burning insulation that is producing this smell. You should discontinue use and call an HVAC technician out right away so they can fix the issue that is manifesting the smell.
Rotten Eggs Smell
This is the biggest cause for concern. As natural gas has no smell, a sulfur smell is added to detect leaks. If you smell rotten eggs in your home coming from the vents, shut off the furnace, open all windows and doors, and leave right away. You will want to contact your gas company to report the leak.
Ultimately, you should call a professional HVAC company to repair what could be going wrong in your system. Contact us for more information.