The first time you turn the furnace on for the winter, it may emit a smell. Some are normal; some indicate that you need service sooner rather than later; and some mean you should call SM Air ASAP. Burning plastic – Something may be overheating. Shut off the furnace and call for service. Burnt toast – Dust has settled on parts of the furnace; once it heats up, the smell will go away. Metallic – Check the floor registers to see if something has been spilled inside them. Musty – This could be mildew in your ductwork or on your filter. Change your furnace filter and schedule a duct cleaning. You don’t want to compromise IAQ (indoor air quality) for good health. If any smell persists, you need to schedule a service call.