What Causes Air Pressure Differences in a Building?

Air leakage occurs when a building envelope has an unsealed opening, like a gap or crack, in the attic or crawl space. Not only that, but there’s also a pressure difference between the indoors and outdoors that causes air to enter or escape through said gap or crack. Here’s a look at the various driving forces that can cause air pressure differences throughout a home or building.

Stack effect. The stack effect refers to air movement into and out of a building due to its buoyancy. As warm air rises and reaches the top of the building, cool outdoor air enters through the ground floor. The reverse of this process occurs when the outside air is warmer than the inside air. Air leakage caused by the stack effect accounts for a significant portion of infiltration in most structures.

Wind pressure. Wind pressure can be a major factor as to why air leakage occurs in homes and buildings. This is especially true if these structures are situated in areas that tend to be windy. When wind blows on a building, outdoor air enters its windward side, while the indoor air escapes on the leeward side.

Vents and related systems. Chimneys, flue vents and exhaust fans push air out of the building during operation, creating negative air pressure. In turn, outdoor air escapes through holes and cracks in the building envelope. Conversely, supply fans that deliver air indoors create positive pressure, causing inside air to be pushed out through the same unsealed openings in the building envelope.

Leaks in ductwork systems. Wear and tear can cause the HVAC ducts to experience punctures and holes, resulting in leaks. These create pressures that increase air leakage in the building envelope. Negative and positive air pressures are created based on the type of duct that was damaged.

At Entergis Testing & Sealing, LLC, our mission is to make our customers as comfortable as possible in their homes or businesses. We specialize in air leakage testing and sealing, providing customized solutions so you can experience better comfort and energy efficiency, as well as improved indoor air quality. Give us a call at (225) 445-2362 or fill out our contact form to schedule an appointment.