If you live in a colder climate, then you know how crucial your furnace is to your family’s comfort, and how frustrating it can be when something goes wrong. There isn’t anything more alarming than turning on your furnace in the winter and experiencing smells coming from it. While some smells coming from your furnace may be a sign of a serious problem, other smells are normal, and may not be a cause for concern. Here are a few examples of smells that you might encounter coming from your furnace, what they mean, and what you can do about them. If you smell sulfur or rotten eggs coming from your furnace, you may have a natural gas leak. Natural gas in its raw form is odorless, and gas companies use additives to alert people of its presence in their homes. If you smell rotten eggs or sulfur coming from your furnace, turn it off right away and contact your gas company. If you smell mold or mildew coming from your furnace, you may have excess moisture in your ductwork. During the summer when you aren’t running your furnace, it is possible for moisture to build up within your ductwork, and when you turn it on, you may smell mildew coming from your furnace. If you are experiencing mildew in your ducts, it may be a good idea to have your ductwork cleaned by an HVAC technician. If you smell burning dust coming from your furnace, this is typically not a cause for concern. During the warmer months, dust can build up inside your furnace and become ignited when you turn your furnace on. This smell is normal, and should go away within a few hours.