What's causing my duct work to pop when the furnace starts or stops? A popping disturbance is a typically sign of an under-sized duct design. It may be caused by greater air flow than the duct work can handle. Have a qualified company analyze your home's ventilation system for proper design and provide a written recommendation. Improper duct work layout can create a number of ventilation and air quality problems, including: loud popping higher energy usage lowered lifespan of the system uneven heating & cooling throughout your home damaged compressor in cooling season overheated unit in the winter In addition, if your ductwork is incorrectly sized you may have other problems, such as leaky ducts and poor layout that impacts airflow. In humid climates this can encourage mold growth within your ductwork.