NEBB Testing, Adjusting and Balancing Certified Technician (CT) key terms

A grid of pitot-tube readings taken at many points across a duct cross-section. The velocity pressures are averaged to find mean velocity, which is then multiplied by duct area to obtain total airflow.

The pressure air exerts perpendicular to duct walls, present whether or not air is moving. Technicians use it to judge fan output, filter loading, and the pressure available at terminal units.

The combined energy of the airstream at a duct location, expressed as static pressure plus velocity pressure. It drops in the direction of flow as friction and fittings absorb energy.

A zone box with a modulating damper and airflow sensor that varies air volume to hold space temperature. Balancing requires setting its maximum and minimum airflow and confirming the sensor reads correctly.

A test in which a duct section is temporarily sealed, pressurized with a calibrated blower, and the airflow needed to hold a specified test pressure is compared against the allowed leakage class.

A sequential method in which branch dampers are set so every terminal carries the same percentage of its design airflow, starting at the hardest-to-feed terminal, then bringing the whole system to design at the fan.

A valve with a calibrated, lockable setting and pressure taps, installed in a hydronic branch or at a coil. Adjusting it while reading pressure drop sets water flow to design.

A control valve containing an internal differential-pressure regulator that holds flow at the commanded value despite system pressure changes, reducing interaction between balancing and temperature control.

A piping layout in which water travels to the farthest terminal and returns by the shortest path, making each circuit roughly equal in length so flows arrive naturally close to balanced.

A hydronic arrangement with separate production and distribution pumps joined by a short common pipe, allowing each loop to run at its own flow rate without disturbing the other.

A small valved fitting in piping that lets a gauge or manometer be connected to read pressure or pressure difference across a coil, valve, or pump without draining the system.

The hydronic branch with the highest pressure loss, which therefore receives the least flow. It is balanced first and becomes the reference for setting every other branch.

A probe with a forward opening that senses total pressure and side openings that sense static pressure. Connected to a manometer, the difference gives velocity pressure and therefore air velocity.

The pressure created by air in motion, obtained as total pressure minus static pressure. It is the quantity a pitot tube measures and converts to velocity using air density.

A fabric or plastic hood placed over a diffuser or grille that directs the entire discharge through a calibrated measuring section, displaying volumetric airflow directly for balancing work.

A velocity probe that calculates airflow from the cooling effect on a heated sensor. It reads low velocities well but needs careful orientation and correction for temperature and direction.

The documented comparison of an instrument's readings against a reference standard of known accuracy, with adjustment when needed. Current records must be available for every instrument used on a project.

Describes a calibration whose reference standard is linked by an unbroken, documented chain of comparisons to a national measurement institute, supporting the credibility of the field measurements taken.

A published constant that converts a measured pressure signal from a flow device, such as a pitot traverse or flow station, into airflow or water flow.

NEBB's published requirements for testing, adjusting, and balancing work, covering minimum procedures, instrument accuracy, measurement methods, and report content that certified firms must follow to produce acceptable reports.

A site visit before formal balancing to confirm equipment is installed, clean, running, and controllable, instruments are calibrated, and design conditions are achievable. Findings are reported before measurements begin.

The form on which raw field readings are recorded, including point identification, instrument used, date, and technician. It is the original record supporting the final report and must be retained.

The deliverable listing design and measured values for each terminal and item of equipment, along with instrument calibration status, noted deficiencies, and the certified firm's signatures.

A running list of items found not in compliance, such as incorrect airflow, missing dampers, or inoperable controls, with dates and responsible parties, used to track resolution before final reporting.

A manually adjustable damper in a branch or at a terminal, set to restrict airflow until measured volume matches design, then locked so the setting is not disturbed.

A damper whose blades rotate toward each other in pairs, so airflow changes nearly in proportion to blade position, which suits volume control and modulating duty.

A manufacturer's graph of fan pressure versus airflow at a stated speed and density. Where it crosses the system curve is the operating point a technician should confirm in the field.

A graph of the pressure a duct system requires at each airflow, rising with the square of flow. Closing dampers or loading filters steepens it and moves the operating point.

Relationships stating that for a given fan and system, airflow varies with speed, pressure with speed squared, and power with speed cubed, used to predict the result of a speed change.

An electronic device that changes motor speed by varying the frequency of the power supplied, letting fan or pump output follow load instead of being throttled by dampers or valves.

A finned-tube heat exchanger in an air stream that heats or cools air using water, steam, or refrigerant. Capacity depends on airflow, fluid flow, and entering air conditions.

A graph relating dry-bulb temperature, wet-bulb temperature, dew point, humidity ratio, enthalpy, and specific volume of moist air, used to verify air conditions and compute coil loads.

The practice of isolating every energy source to a piece of equipment and applying personal locks and tags so it cannot be started or energized while work is underway.

A space with limited entry and exit that is not meant for continuous occupancy. Entry may require atmosphere testing, a permit, an attendant, and rescue provisions.

Gloves, eye and hearing protection, hard hat, foot protection, and respiratory protection chosen for the hazards of the task, inspected before use and worn as required by the site.

A step-by-step review of a task that identifies hazards and the controls to be used, completed with the crew before work begins and revised when site conditions change.

Advance communication with mechanical, electrical, controls, and commissioning contractors to schedule access, share test results, and resolve conflicts so balancing is not blocked or repeated.