man watching air flow

Understanding Air Flow For A More Energy Efficient Building

Want to strike a balance between having your building reach its optimal energy efficiency and creating a climate that’s comfortable for every person in it? It all starts with understanding air flow.

As air moves and flows, it tries to create a balance between the high and low air pressure areas. If there is a gap and a pressure difference, it will move through that path whether we want it to or not.
To control the air flow, we put up barriers – materials – in order to control or block the air from moving through it. The more we choose to control the air flow, the tighter the blockage must be. Even the smallest of gaps can allow leakage, which will continue to build over time.
If the amount of air removed from an area does not equal the amount of air supplied to that space, then a pressure imbalance occurs.
In all climates, a balanced air pressure is ideal, yet is difficult to maintain. In warm climates, a slight positive pressure is preferred, while in cold climates, a slight negative pressure can help prevent hidden moisture problems building up in remote areas of the building.
A negative air pressure happens when more air is removed than is added. Leaky ducts can create negative pressure by allowing air to flow where its not intended, and allows it to accumulate behind walls, under floors, or in crawl spaces. In summer, the results show as hot, humid air infiltration. In winter, it means cold drafts. If the negative air pressure becomes large enough, it can lead to dangerous backdrafting around flues of combustion appliances.
A positive air pressure happens when more air is brought in than is removed from the space. It can be controlled with a fresh air intake.
While a building rarely achieves a balanced air pressure throughout the spaces, likewise it rarely is balanced in such a way that a negative or positive charge remains dominate from floor to floor, one side to the other. Instead, you’ll usually find pockets of air impacting the building in different ways.
An example would be closing off office space in which there is a register delivering air, but has no return flow in place. This would allow a positive air pressure to continue building in place.
This is also how indoor air quality is impacted. That same space that continually builds up a positive air flow can also allow higher levels of pollutants to accumulate as well. Intake flows can bring in outside pollutants – pesticides, gases, chemicals, carbon monoxide – especially in industrial locations. It can also allow other types of indoor air pollutants to form and grow – mold spores, dust mites, bacteria, viruses – and keep them in concentrated areas of the building. Over time, these substances can leak into other parts of the building, and begin circulating, reducing the air quality overall.


Not sure how the air flow in your building is impacting your energy efficiency? The best place to start is with an energy audit. One of our HVAC technicians can easily share with you where even the smallest of corrections can make the biggest impacts over time.

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