Variable Air Volume (VAV) Boxes in Commercial Buildings

Variable Air Volume (VAV) boxes are zoning devices that regulate airflow to specific areas of a building. As terminal units, they vary the amount of conditioned air delivered to a space in response to local demand, allowing multiple zones to operate at different temperatures from the same air-handling and ventilation system. To learn about inspection procedures and common defects, take the Inspecting Commercial HVAC Systems Online Course.

Rather than supplying a fixed amount of air to every space, VAV systems adjust airflow at the zone level to match heating or cooling needs. This approach supports more consistent interior conditions and improved energy efficiency. Many VAV boxes also include reheat components to manage temperature at the zone level.

Inspecting VAV Boxes

In this video, the VAV boxes are exposed below the ceiling and are controlled by simple wall-mounted thermostats serving adjacent rooms. The thermostat signals a low-voltage valve to allow hot water flow and temper the supply air when heat is required. Airflow is continuous; the air is not shut off and flows throughout the building.

At this specific property, inspectors can document the presence of VAV boxes and operate the thermostats to verify basic HVAC operation. However, VAV boxes are often concealed above suspended ceiling tiles, limiting the visibility of the units without moving ceiling tiles. Since VAV boxes rely on upstream equipment, such as boilers, chillers, or cooling towers, inspectors may coordinate with specialty consultants for a more comprehensive assessment of the HVAC system as a whole. The How Air Handling Units (AHU) Work video reviews how the VAV boxes operate as part of the overall HVAC system at this recreational facility. For a downloadable inspection procedure guide, refer to the AHU and VAV Box Inspection Checklist.

HVAC System Analyses

Some commercial buildings, such as the one shown in the video, a Building Automation System (BAS) may also be present. A BAS is a centralized platform used to monitor and control building systems, most commonly HVAC, from a single interface. Reviewing BAS data typically requires coordination with the person(s) with the most knowledge about property or a specialty consultant to properly interpret system information.

The image below shows a VAV box as displayed in the BAS software, overseen by the facility manager for this property.

BAS software view of the VAV box shown in the video.

Additionally, Testing, Adjusting, and Balancing (TAB) analysis services are performed to verify that an HVAC system delivers the designed airflow, temperatures, and pressure relationships throughout the building. These are done by qualified HVAC and TAB professionals.

Commercial HVAC Inspection Training

Learn more about inspecting VAV systems in the Inspecting Commercial HVAC Systems Online Course, which includes a downloadable coursebook, inspection checklists, and a certificate upon completion.