If you smell an odd burning smell when you first start your heater, it may be the dust burning of the heat exchanger or heating elements. But if you smell gas or any odd smells persist longer than on startup, you may have problems requiring a professional furnace repair service. Also, looking at your furnace for other potential issues, such as leaks in the flue pipes or gas lines, is essential. Older furnaces could also have leaks in the heat exchanger, allowing carbon monoxide into your home. We also check smoke and carbon monoxide detectors.