Why does my ductwork make popping sounds?

Ductwork popping sounds are typically caused by thermal expansion and contraction as your HVAC system cycles on and off. When heated or cooled air flows through metal ducts, the temperature changes cause the metal to expand and contract, creating those distinctive popping or ticking noises.

The most common cause is undersized or improperly supported ductwork. When ducts are too small for the airflow volume, they can flex and "oil can" - bowing in and out like the bottom of an oil can when pressed. This creates loud popping sounds, especially when the system first starts up. Similarly, ducts that aren't properly secured with hangers or strapping can move and pop as air pressure changes.

Temperature differentials make the problem worse during Ottawa's extreme seasons. In winter, when your furnace pushes 120°F air through ducts in a cold basement or crawl space, the rapid temperature change causes significant expansion. The same happens in reverse during summer with cold AC air. Poorly insulated ducts in unconditioned spaces are particularly prone to this issue.

Loose or damaged ductwork connections can also create popping sounds. Over time, duct joints can separate slightly, and the flexible movement at these connections produces noise. Additionally, if your return air ducts are undersized, they can create negative pressure that causes supply ducts to collapse inward and pop back out.

While popping sounds are usually harmless, they indicate your duct system isn't operating efficiently. This can lead to uneven heating and cooling, higher energy bills, and unnecessary wear on your HVAC equipment. In Ottawa's climate, proper ductwork is essential for comfort and efficiency.

A licensed HVAC technician can diagnose the exact cause by inspecting your ductwork for proper sizing, support, and sealing. Solutions might include adding duct supports, increasing duct size, or improving insulation. For a professional assessment of your ductwork, request a quote from Ottawa HVAC Pro.