1 Scope
NOTE This standard covers independent third-party testing, adjusting, and balancing (TAB) of HVAC air-distribution and hydronic-distribution systems. (1.1)
NOTE The work includes verification that installed equipment performs in accordance with the contract documents at design conditions, the measurement and recording of air and water flow rates throughout the distribution systems, the adjustment of balancing devices to bring measured flows into agreement with design flows within the tolerances established in this standard, the documentation of the as-balanced condition in a TAB report, and the issuance of deficiency reports to the installing contractors and the Engineer of Record where measured performance cannot be brought into compliance by adjustment alone. (1.2)
1.3 TAB shall be performed after the air and hydronic systems are mechanically complete, flushed, cleaned, and started up, after the controls contractor has completed point-to-point checkout and placed the building automation system in a state suitable for balancing, and after the building envelope is substantially closed.
1.4 The relationship between TAB and commissioning shall conform to ASHRAE Guideline 0 and the project-specific Commissioning Plan where one exists.
NOTE TAB is distinct from building commissioning, which is a broader scope including design-intent review, construction observation, functional performance testing of integrated systems, and operator training led by an independent Commissioning Authority; the TAB report is one input the CxA uses to verify system performance and is not itself commissioning. (1.5)
1.6 The TAB Contractor shall coordinate the sequence of TAB activities with the Engineer of Record, the Mechanical Contractor, the Controls Contractor, the Commissioning Authority (where one is engaged), and the General Contractor.
1.8 Governing Procedural Standard
● NEBB Procedural Standards for Testing, Adjusting, and Balancing of Environmental Systems (current edition)
○ AABC National Standards for Total System Balance (current edition)
○ ASHRAE 111, Measurement, Testing, Adjusting, and Balancing of Building HVAC Systems (current edition)
2 Referenced Standards
2.1 Testing, adjusting, balancing, instruments, and reporting shall comply with the latest editions of the following standards adopted by the project jurisdiction.
2.2 Where a specific edition is referenced in the contract documents or in the project Commissioning Plan, that edition shall govern.
| Standard |
Title |
| NEBB Procedural Standards |
NEBB Procedural Standards for Testing, Adjusting, and Balancing of Environmental Systems (current edition) |
| AABC National Standards |
AABC National Standards for Total System Balance (current edition) |
| ASHRAE 111 |
Measurement, Testing, Adjusting, and Balancing of Building HVAC Systems |
| ANSI/SMACNA 023 |
HVAC Systems — Testing, Adjusting, and Balancing |
| ANSI/ASHRAE/IES 90.1 |
Energy Standard for Buildings Except Low-Rise Residential Buildings — commissioning and verification provisions cross-reference |
| ASHRAE 62.1 |
Ventilation and Acceptable Indoor Air Quality — outdoor airflow verification |
| ASHRAE Guideline 0 |
The Commissioning Process |
| ASHRAE Guideline 1.1 |
HVAC&R Technical Requirements for the Commissioning Process |
| ANSI/AMCA 203 |
Field Performance Measurement of Fan Systems |
| ANSI/AMCA 610 |
Laboratory Methods of Testing Airflow Measurement Stations for Performance Rating |
| ANSI/HI 14.6 |
Rotodynamic Pumps for Hydraulic Performance Acceptance Tests — field test references |
| ANSI/SMACNA 016 |
HVAC Air Duct Leakage Test Manual — coordination reference |
| NFPA 90A |
Standard for the Installation of Air-Conditioning and Ventilating Systems |
| IMC |
International Mechanical Code (current adopted edition) |
3 Submittals
3.1 Action Submittals
3.1.1 The TAB Contractor shall submit the following items for the Engineer's review and acceptance before mobilizing TAB field work:
- TAB Agency qualifications, including current NEBB or AABC firm certification, the certificate number, and the certification expiration date
- TAB Supervisor qualifications, including the name of the certified TAB Supervisor (NEBB-CP or AABC-TBE) assigned to the project, the certification number, and a resume of comparable projects
- Field technician roster, including the names and qualifications of the personnel who will perform field measurements under the TAB Supervisor's direction
- Instrument list, identifying each instrument by manufacturer, model, serial number, last calibration date, calibration agency, and the next calibration due date
- Preliminary TAB Report (the "agenda" or "pre-balance" report) — see the Preliminary Report section of this standard
- Project-specific TAB Plan, including the sequence of system balancing, the proposed test pressures, the proposed forms and field-data sheets, the format of the final report, and the proposed schedule for field work
- Sample blank report pages for each system type to be balanced, showing the data fields that will be recorded
☑ TAB Agency certification (NEBB or AABC)
☐ TAB Supervisor certification and resume
☐ Field technician roster and qualifications
☐ Instrument list with calibration dates
☐ Preliminary TAB Report (agenda)
☐ Project-specific TAB Plan and schedule
☐ Sample blank report forms
3.1.2 No field TAB work shall commence until the action submittals have been reviewed and returned with no outstanding engineering questions.
3.2 Closeout Submittals
3.2.1 The TAB Contractor shall provide the following at or before substantial completion of the TAB scope:
- Final TAB Report, in the format established in this standard, signed and sealed by the certified TAB Supervisor
- Instrument calibration certificates for all instruments used on the project, current as of the date of field measurements
- Deficiency reports issued during the course of the work, with a final disposition note for each indicating whether the deficiency was corrected, accepted as-is by the Engineer, or remains open at the time of report issuance
- Marked-up record drawings indicating the location, tag, and final set position of every balancing device adjusted by the TAB Contractor, including the locked-handle position of every manual volume damper and the turns-from-closed position of every manual balancing valve
- Re-test reports for any system or component re-balanced after the initial Final Report
- Where seasonal balancing is included in the scope, the seasonal re-balance report, issued during the opposite operating mode (heating season for a system first balanced in cooling, or cooling season for a system first balanced in heating)
☐ Final TAB Report, signed and sealed by TAB Supervisor
☑ Instrument calibration certificates
☑ Deficiency reports with final disposition notes
☑ Marked-up record drawings of balancing-device positions
☐ Re-test reports for re-balanced systems
☐ Seasonal re-balance report (where in scope)
4 Quality Assurance
4.1 TAB Agency Qualifications
4.1.1 The TAB Contractor shall be an independent firm whose principal business is the testing, adjusting, and balancing of HVAC and plumbing systems.
4.1.2 The TAB Contractor shall be currently certified by the National Environmental Balancing Bureau (NEBB) or the Associated Air Balance Council (AABC).
4.1.3 The TAB firm shall not be owned by, affiliated with, or financially controlled by the Mechanical Contractor, the Controls Contractor, the Sheet Metal Contractor, or any other contractor performing installation work on the project, and shall not be a subsidiary or division of the General Contractor.
NOTE Independence is required to ensure that the TAB Contractor's deficiency reports are issued without conflict of interest. (4.1.4)
4.1.5 Agency Certification Selection
○ NEBB certified firm
○ AABC certified firm
● NEBB or AABC certified firm — TAB Contractor's choice
● Required — TAB firm shall be independent of all installing contractors
○ Not required — TAB may be performed by a division of the Mechanical Contractor (small projects only)
4.2 TAB Supervisor Qualifications
4.2.1 The TAB field work shall be supervised by a Certified TAB Supervisor (NEBB-CP — Certified Professional, or AABC-TBE — Test and Balance Engineer) who is a full-time employee of the TAB Agency.
4.2.2 The TAB Supervisor shall be present on-site during the execution of the air-and-water proportional balance.
4.2.3 The TAB Supervisor shall personally witness or perform the final readings reported in the Final TAB Report.
4.2.4 The TAB Supervisor shall sign and seal the Final TAB Report.
4.2.5 The Supervisor's certification shall be current and shall not be permitted to lapse during the project.
4.3 TAB Technician Qualifications
4.3.1 Field measurements may be taken by TAB technicians who are direct employees of the TAB Agency and who have received documented training in the use of the specific instruments used on the project.
4.3.2 Technicians shall work under the direction of the TAB Supervisor and shall not be authorized to issue final readings or sign the Final TAB Report.
4.3.3 Apprentices in training may operate instruments under direct technician or Supervisor oversight.
4.4 Conflict of Interest
4.4.1 The TAB Contractor shall not perform installation work, manufacturer's representation, or controls programming on the same project for which it is providing TAB services.
4.4.2 Where a single firm offers both commissioning and TAB services, the firm may provide both on the same project only where the Engineer and Owner explicitly approve the dual scope in writing and where the commissioning team and TAB team are organizationally separate within the firm.
5 Environmental and Service Conditions for TAB Work
5.1 Building Readiness
5.1.1 TAB field measurements shall be performed only when the building and systems are in a state representative of the design operating condition.
5.1.2 The TAB Contractor, with the Mechanical Contractor and the General Contractor, shall confirm the readiness conditions for air systems, hydronic systems, controls, and the building envelope listed below before beginning field measurements on any system.
NOTE For air systems: ductwork is complete and pressure-tested where required by
Hvac Ductwork; air handling units are started, filters are installed and clean, coils are clean and free of construction debris, belt drives are aligned and tensioned, terminal units are installed and powered, and air distribution devices are installed.
(5.1.2.1) NOTE For hydronic systems: piping is complete, flushed, cleaned, and chemically treated as specified in
Hydronic Piping; pumps are started and rotating in the correct direction; coils are connected and open to flow; air has been removed from high points; expansion tanks are properly charged.
(5.1.2.2) NOTE For controls: BAS has been installed, point-to-point checkout is complete, control valves stroke fully open and fully closed on command, dampers stroke fully open and fully closed on command, VFDs respond to speed commands, and override capability is available to the TAB Contractor to drive systems to test conditions independently of normal sequences. (5.1.2.3)
NOTE For the building envelope: exterior windows, doors, and curtain wall are substantially in place; major envelope openings are closed; stack effect and infiltration are representative of occupied conditions. (5.1.2.4)
☑ Ductwork complete, pressure-tested where required
☐ Air handlers started, filters clean, coils clean
☐ Hydronic piping flushed, cleaned, chemically treated
☐ Pumps started, rotation verified
☐ Air vented from hydronic high points
☐ BAS point-to-point checkout complete
☐ Controls override available to TAB Contractor
☐ Building envelope substantially closed
5.1.3 TAB measurements taken before these readiness conditions are met do not reflect the as-balanced condition the Owner will experience and are not acceptable as final readings.
5.2 Ambient Conditions During Air Balance
5.2.1 Air-side balancing shall be performed under stable building pressure conditions, with doors to the exterior closed, freight openings not open during readings, and significant exhaust systems not part of the system being balanced in their normal operating state.
5.2.2 Outdoor air dampers shall be at the minimum-position setting for normal-occupied operation when minimum outdoor air is being verified, and at full open when economizer-mode performance is being verified.
5.3 Ambient Conditions During Hydronic Balance
5.3.1 Hydronic balancing shall be performed with the system at or near a representative load.
5.3.2 Flow readings shall be taken with the affected control valve commanded fully open at the coil, with all upstream and downstream balancing devices in their normal operating state, and with the system pump operating at the speed and head condition that produces the design flow at the affected branch.
5.3.3 Pressure-independent control valves shall be operated with the controller commanding the valve to its full design flow set-point.
6 Instruments and Calibration
6.1 General Instrument Requirements
6.1.1 Instruments used to record values reported in the Final TAB Report shall be appropriate to the parameter measured, of accuracy class adequate for the tolerance specified in this standard, in good repair, and calibrated within the interval established below.
6.1.2 The TAB Contractor shall record on each field data sheet the instrument used for each measurement, including its serial number, so that the Engineer can trace any disputed reading back to the specific instrument and its calibration record.
6.2 Calibration Interval
6.2.1 Each instrument used by the TAB Contractor shall be calibrated against a known reference traceable to NIST (National Institute of Standards and Technology) standards or equivalent.
6.2.2 The maximum calibration interval shall be six months for primary measuring instruments (pitot tubes and manometers for duct traverse, rotating vane anemometers, hot-wire anemometers, flow hoods, electronic micromanometers, ultrasonic flow meters, and pressure transducers) and twelve months for secondary instruments (digital thermometers, hygrometers, tachometers, clamp-on ammeters, and rotation indicators), or the manufacturer's recommended interval if shorter.
6.2.3 Calibration shall be performed by a calibration laboratory accredited to ISO/IEC 17025 or by the instrument manufacturer's certified service center.
6.2.4 Calibration Interval Set-Points
● NIST-traceable, ISO/IEC 17025 accredited laboratory
○ Manufacturer's certified service center, NIST-traceable
6.3 Required Instrument Categories
6.3.1 The TAB Contractor shall provide and maintain in calibrated condition, at a minimum, the following instruments:
- Pitot tube and electronic micromanometer for duct traverse measurement, with manometer resolution of 0.001 in. w.g. or finer and range covering the duct velocity pressures expected on the project
- Rotating vane anemometer for face-velocity measurement at grilles, registers, and diffusers
- Hot-wire (thermal) anemometer for low-velocity measurement and outdoor air intake traverse
- Flow hood (balometer) for direct-reading airflow at diffusers and grilles, calibrated for the diffuser pattern types in use
- Direct-reading digital manometer for static pressure measurement at filter banks, coils, and fans
- Tachometer (contact or photo type) or strobe tachometer for fan and pump rotational speed
- Clamp-on AC ammeter and voltmeter, true-RMS type, for motor electrical measurements
- Digital thermometer with appropriate sensors (immersion, surface, air) for water and air temperature measurement
- Hygrometer or psychrometer for air humidity measurement
- Ultrasonic flow meter or insertion-type flow meter for hydronic field flow verification at flow stations and at branches without dedicated flow stations
- Differential pressure gauge set for hydronic balancing valve flow determination using manufacturer flow curves
- Sound level meter (Type 2 minimum) where sound-level spot checks are within the TAB scope
6.3.2 Instruments not on this list, including newer technology not yet enumerated, may be used where appropriate to the measurement and where calibrated to the standards above.
7 Sequencing and Coordination
7.1 TAB Position in the Construction Sequence
NOTE TAB field work follows the completion of installation, startup, and controls checkout, and precedes functional performance testing by the Commissioning Authority where one is engaged. (7.1.1)
7.1.2 General Construction Sequence
NOTE The general sequence is: (7.1.2.1)
- Mechanical and electrical installation complete; ductwork pressure-tested; hydronic piping flushed and chemically treated
- Equipment startup by installing contractor or manufacturer's representative; rotation, lubrication, and initial trim of belt drives confirmed
- Controls point-to-point checkout complete by Controls Contractor; BAS in service with override capability available to TAB Contractor
- Preliminary TAB Report submitted by TAB Contractor; pre-balance walk-through with Engineer and Mechanical Contractor
- Field TAB work, with deficiency reports issued in real time
- Re-balance after deficiency corrections by installing contractors
- Final TAB Report submitted, signed, and sealed by TAB Supervisor
- Functional performance testing by Commissioning Authority, using Final TAB Report as a baseline
- Seasonal re-balance, where included in scope, during the opposite-season operating mode
7.1.3 The Mechanical Contractor shall not request final inspection or substantial completion of the HVAC scope until the Final TAB Report has been issued and accepted.
7.2 Pre-Balance Walk-Through
7.2.1 Before mobilizing field work, the TAB Supervisor shall conduct a pre-balance walk-through with the Engineer of Record and the Mechanical Contractor to verify that the equipment, instruments, and balancing devices required by the design are present and accessible.
7.2.2 Items inspected during the pre-balance walk-through shall include the presence and accessibility of every manual volume damper and balancing valve shown on the contract drawings, the location and labeling of every flow station, the accessibility of pressure ports at coils and pumps, the operability of access doors at duct measurement locations, and the availability of permanent test ports where required by the contract documents.
7.2.3 Missing or inaccessible devices identified during the pre-balance walk-through shall be installed or made accessible by the Mechanical Contractor before TAB field work begins.
7.3 Coordination with the Controls Contractor
7.3.1 The TAB Contractor shall work in close coordination with the Controls Contractor during field balancing.
7.3.2 The Controls Contractor shall provide the TAB Contractor with the override capability required to command air terminal units to design maximum and design minimum airflow, to command VFD speeds independently of the normal sequence, and to drive the outdoor air damper to its minimum-position and economizer-open positions on command.
7.3.3 The Controls Contractor shall be available during the TAB field work to address controller-side issues.
7.4 Coordination with the Commissioning Authority
7.4.1 Where a Commissioning Authority (CxA) is engaged on the project, the TAB Contractor shall coordinate the schedule and scope of TAB work with the CxA in accordance with the project Commissioning Plan.
7.4.2 The CxA may witness selected TAB field readings on a sampling basis, at the percentage established in the Commissioning Plan.
NOTE TAB is not commissioning; the TAB Report is a substantive input to the commissioning process, and the CxA's functional performance tests build on the as-balanced condition documented in the TAB Report. (7.4.3)
7.4.4 Witness Sampling Rate
8 Air System Procedures
8.1 Air-Side Balance Tolerance
8.1.1 The TAB Contractor shall adjust air-distribution systems so that the measured airflow at each terminal device (diffuser, register, grille, or air terminal unit) and at each balancing point falls within ±10% of the design airflow indicated on the contract drawings, with the total fan airflow within ±10% of the design supply airflow.
8.1.2 Measured outdoor airflow at minimum-position settings shall be within +10%/-0% of the design minimum outdoor airflow.
NOTE The system shall not be balanced low on outdoor air, because outdoor air is required for code-mandated ventilation and indoor air quality. (8.1.3)
8.1.4 Air-Side Tolerance Set-Points
● +10% / -0% — outdoor air shall not fall below design minimum
○ +10% / -5% — limited under-delivery permitted with Engineer approval
○ ±10% — symmetric tolerance (not recommended where ASHRAE 62.1 compliance is required)
8.1.5 Where measured airflow cannot be brought within the tolerance by adjustment of dampers within the system, the TAB Contractor shall not artificially close upstream devices to redistribute flow at the cost of fan static pressure margin.
8.1.6 Where flow cannot be brought into tolerance, the TAB Contractor shall instead issue a deficiency report identifying the root cause (excessive system pressure drop, undersized duct, fan curve mismatch, missing fittings) and shall continue field work on systems that can be brought into balance while the deficiency is being addressed.
8.2 Duct Traverse for Fan Airflow Verification
8.2.1 Total fan airflow shall be measured by pitot-tube traverse in conformance with ANSI/AMCA 203, at a location with the minimum upstream and downstream straight-duct runs required for stable, fully developed flow.
8.2.2 The traverse location shall be at least 7.5 hydraulic diameters downstream of any disturbance and 2 hydraulic diameters upstream of any disturbance where possible, and the AMCA 203 Class 1, 2, or 3 designation shall be recorded on the traverse data sheet to disclose the quality of the measurement location.
8.2.3 Duct Traverse Method
● Pitot tube traverse per ANSI/AMCA 203, Class 1 location preferred
○ Permanent airflow measurement station (AMCA 610 listed) where installed
○ Sum of terminal device readings (small low-pressure systems only, with Engineer approval)
8.2.4 Traverse points shall be located in conformance with the log-Tchebycheff or equal-area method for the duct cross-section.
8.2.5 The number of traverse points shall be 16 minimum for rectangular ducts and 16 minimum (on two perpendicular diameters) for round ducts, with closer spacing where the duct dimension exceeds the standard traverse spacing.
8.2.6 Each traverse point shall be recorded as a velocity pressure, and the average velocity pressure shall be converted to velocity using the standard pitot equation with a correction for non-standard air density where the air temperature, elevation, or barometric pressure depart materially from standard conditions.
8.3 Terminal Device Measurement
8.3.1 Airflow at supply diffusers, return grilles, and exhaust grilles shall be measured using a flow hood (balometer) appropriate to the diffuser pattern, or by face-velocity traverse with a rotating vane or thermal anemometer where the device geometry is incompatible with a flow hood.
8.3.2 When a flow hood is used, the hood shall be seated fully against the ceiling or wall surface to prevent leakage around the rim, and the hood shall be selected and configured for the device pattern in accordance with the hood manufacturer's instructions for the device type.
8.3.3 Where a manufacturer's correction factor (K-factor) is published for the specific diffuser type and the flow hood being used, the factor shall be applied and noted on the field data sheet.
8.3.4 For perforated face and slot diffusers, the Ak (effective area) method using a manufacturer-published Ak coefficient and a face-velocity measurement is acceptable.
NOTE The Ak method is sometimes more accurate than a flow hood because of the flow disturbance the hood creates at the diffuser face. (8.3.5)
8.3.6 The TAB Contractor shall record the measurement method used at each device on the report.
8.3.7 Terminal Device Measurement Method
● Flow hood (balometer) with diffuser-specific correction factor
○ Face-velocity traverse with rotating vane anemometer (Ak method)
○ Face-velocity traverse with thermal anemometer (low velocity)
8.4 Air Terminal Unit (VAV Box) Balance
8.4.1 Air terminal units shall be balanced by commanding the box to its design maximum airflow using BAS override, measuring the resulting airflow at the box discharge or at the served diffusers, and adjusting the box controller's maximum-airflow set-point or its flow-sensor scaling factor to bring the measured airflow into agreement with the design value.
8.4.2 The procedure shall be repeated at the design minimum airflow set-point.
8.4.3 Pressure-independent boxes that fail to maintain their commanded flow within the box's own performance tolerance shall be reported as deficient back to the Controls Contractor for flow-sensor recalibration or replacement.
8.4.4 VAV Box Balance Set-Points
☑ Design maximum cooling airflow
☐ Design minimum cooling airflow
☐ Design maximum heating airflow (where heating function exists)
☐ Design minimum outdoor air per ASHRAE 62.1 (DCV systems)
8.5 Outdoor Air Verification
8.5.1 Minimum outdoor airflow shall be verified at the outdoor air intake or at a dedicated outdoor air measuring station, with the unit operating at its minimum-position outdoor air damper setting and the return air damper at the corresponding modulated position.
8.5.2 The TAB Contractor shall record both the measured outdoor airflow and the measured supply airflow at the time of the reading, so that the outdoor air fraction can be calculated.
8.5.3 Where the unit serves multiple zones with demand-controlled ventilation (DCV), the verification shall be performed at the maximum total zone outdoor air demand corresponding to the design occupancy.
8.5.4 Outdoor Air Verification Method
● Dedicated permanent outdoor air measuring station (AMCA 610 listed)
○ Pitot traverse at outdoor air duct
○ Hot-wire anemometer traverse at the outdoor air intake
○ Temperature-balance calculation (mixed-air temperature method)
8.5.5 The temperature-balance (mixed-air) method of estimating outdoor airflow from return-air, outdoor-air, and mixed-air temperatures is permitted only as a check, not as the primary measurement.
NOTE The temperature-balance method is sensitive to small temperature differences and is unreliable when the outdoor-to-return temperature differential is less than 10 °F. (8.5.6)
8.6 Fan Curve and System Operating Point Verification
8.6.1 The TAB Contractor shall verify that each fan operates at a point on its certified fan curve consistent with the design intent.
8.6.2 The verification shall record the measured total fan airflow, the measured fan total static pressure (or fan external static pressure, with internal losses added per the manufacturer's data), the measured fan speed (RPM), the measured motor amperage and voltage, and the calculated brake horsepower.
8.6.3 The measured operating point shall be plotted on the manufacturer's certified fan curve and compared to the design operating point.
8.6.4 Operation more than 10% from the design point in airflow or static pressure shall be reported as a deficiency with the suspected cause (excess system pressure drop, dirty filter or coil, blocked duct, fan curve mismatch).
☑ Measured airflow (from traverse)
☐ Fan total static pressure
☐ Fan external static pressure
☐ Fan RPM
☐ Motor amperage (all three phases)
☐ Motor voltage (line-to-line)
☐ Calculated brake horsepower
☐ Operating point plotted on certified fan curve
8.7 Fume Hood and Containment Verification
8.7.1 Where the project includes fume hoods, biosafety cabinets, or other containment devices specified by the laboratory or research program, the TAB Contractor shall verify face velocity at fume hoods (typically 80–120 fpm at the design sash position, but shall conform to the project program), exhaust airflow at biosafety cabinets, and pressure differentials between containment rooms and adjacent spaces.
8.7.2 Containment verification shall be performed in coordination with the laboratory program manager and shall not substitute for ASHRAE 110 fume hood acceptance testing where that testing is separately required.
9 Hydronic System Procedures
9.1 Hydronic Balance Tolerance
9.1.1 The TAB Contractor shall adjust hydronic systems so that the measured water flow at each coil, terminal unit, or balancing point falls within ±10% of the design flow indicated on the contract drawings, with total system flow at each pump within ±10% of the design pump flow.
9.1.2 Pressure-independent control valves (PICVs) that are pre-set at the factory or in the field to a specified maximum flow shall be verified at the pre-set value within the valve manufacturer's published accuracy band, which is typically tighter than ±10%.
9.1.3 Hydronic Tolerance Set-Points
9.2 Flow Station Readings
9.2.1 Where the contract drawings indicate dedicated flow measurement stations (orifice plates, venturi meters, multi-port averaging pitots, or AMCA 610-equivalent water flow stations) at pump discharges, main branches, or large coils, flow shall be measured at the flow station using the differential-pressure signature and the station manufacturer's flow curve.
9.2.2 The TAB Contractor shall record the measured differential pressure, the calculated flow, and the station serial number on the data sheet.
9.2.3 Field-installed flow stations require representative upstream and downstream straight pipe run, and the TAB Contractor shall record the as-installed straight run condition for reference.
9.2.4 Primary Hydronic Flow Measurement Method
● Permanent flow station (orifice, venturi, or multi-port averaging) — preferred
○ Clamp-on or insertion ultrasonic flow meter (TAB Contractor's instrument)
○ Pressure-drop across coil with manufacturer-published coil flow curve
○ Manual balancing valve differential-pressure signature with valve manufacturer's flow curve
9.3 Coil Balancing Valve Adjustment
9.3.1 At each coil with a manual balancing valve (calibrated balancing valve, double-regulating valve, or globe valve serving the balance function), the TAB Contractor shall measure the flow using the valve's differential-pressure signature interpreted against the valve manufacturer's published flow curve, and shall adjust the valve handle (turns from closed, or memory stop set-position) until the measured flow is within tolerance of the design value.
9.3.2 The final handle position shall be locked using the valve's memory stop or position-lock feature and shall be recorded on the report and on the marked-up record drawings.
9.3.3 The proportional-balance method (NEBB / AABC standard procedure) shall be used for branch and coil balancing: the most-restricted (lowest %-of-design) branch is identified, all branches are set to a common percentage of design, and the pump impeller, VFD speed, or main throttling valve is adjusted to bring the system into balance with all branch valves open as wide as possible.
NOTE Closing branch valves to throttle high-flow circuits while leaving the pump in its as-found condition wastes pump energy and is not the preferred balance method. (9.3.4)
9.3.5 Coil Balancing Valve Type
☑ Manual calibrated balancing valve (double-regulating, with DP ports)
☐ Manual globe-type balancing valve (no DP ports — Cv-based)
☐ Automatic flow-limiting cartridge valve (factory pre-set)
☐ Pressure-independent control valve (PICV) — combines control and balance
9.4 Pump Curve and System Operating Point Verification
9.4.1 The TAB Contractor shall verify that each pump operates at a point on its certified pump curve consistent with the design intent.
9.4.2 The verification shall record the measured pump suction pressure, discharge pressure, calculated total dynamic head (TDH), the measured pump speed (RPM), the measured motor amperage and voltage, and the calculated brake horsepower.
9.4.3 Flow shall be determined either from a permanent flow station, by ultrasonic flow meter, or by reading the pump head against the pump curve where the pump curve is shape-suitable for this method (steep-curve pumps only — flat-curve pumps cannot be reliably converted from head to flow).
9.4.4 The measured operating point shall be plotted on the manufacturer's certified pump curve and compared to the design operating point.
☑ Pump suction pressure
☐ Pump discharge pressure
☐ Total dynamic head (calculated)
☐ Pump flow (from flow station or ultrasonic meter)
☐ Pump RPM
☐ Motor amperage (all three phases)
☐ Motor voltage (line-to-line)
☐ Calculated brake horsepower
☐ Operating point plotted on certified pump curve
9.5 Variable-Speed Pump Verification
9.5.1 For variable-speed pumps, the TAB Contractor shall verify operation at design conditions and at part-load conditions representative of the system's intended operating range.
9.5.2 Differential-pressure setpoints for variable-speed pump control shall be verified at the location of the controlling sensor, and the part-load pump speed and motor amperage shall be recorded at one or more part-load points.
9.5.3 Where pump speed at design flow exceeds 95% of nameplate, the TAB Contractor shall flag the condition as a deficiency because the system has no remaining capacity to respond to fouling, future expansion, or unforeseen pressure drop.
9.6 Chilled-Water and Hot-Water Coil Verification
9.6.1 For each major coil (air-handling unit coils, large terminal coils), the TAB Contractor shall verify entering and leaving water temperatures, entering and leaving air temperatures, water flow, and air flow simultaneously at a representative load.
9.6.2 The measured heat-transfer rate (Q = m·c·ΔT for both water and air sides) shall agree between the two sides within the accuracy of the temperature measurements (typically within ±5–10% when measured carefully).
9.6.3 Coil performance reported below design that cannot be explained by water flow or air flow shortfalls shall be reported as a deficiency for investigation of fouling, air entrainment, or fin damage.
○ Required for each major coil (AHU coils, large terminal coils)
● Required for AHU coils only
○ Not required — flow verification only, performance verified by Cx
10 Sound and Vibration Spot Checks
10.1 Where the contract documents include space-by-space sound criteria (NC, RC, or dBA) and require TAB sound measurements, the TAB Contractor shall take sound-level readings using a Type 2 (or better) sound level meter in selected representative spaces, with the system operating in its normal mode, and shall compare the measured levels to the design criteria.
NOTE Sound measurements taken by the TAB Contractor are spot checks; comprehensive acoustical testing and noise-criterion compliance verification by frequency band is a separate acoustical-engineering scope. (10.2)
10.3 Vibration spot checks may include simple displacement or velocity readings on fan and pump bearings to verify that no obvious vibration anomaly is present at the time of TAB.
10.4 Sound and Vibration Scope Selection
○ Included — spot sound and vibration checks at representative locations
○ Sound checks only
● Not included — acoustical testing performed by separate acoustical engineer
11 Deficiency Reporting
11.1 Issuance and Distribution
11.1.1 The TAB Contractor shall issue a deficiency report whenever a measured condition cannot be brought into compliance with the design intent by adjustment of devices within the scope of TAB.
11.1.2 Deficiency reports shall identify the affected system or device, the design value, the measured value, the suspected root cause, and the responsible party (Mechanical Contractor, Sheet Metal Contractor, Controls Contractor, manufacturer, or design — referred back to the Engineer of Record).
11.1.3 Deficiency reports shall be issued in real time as deficiencies are identified, not aggregated and held until the Final Report.
11.1.4 Distribution shall include the General Contractor, the responsible installing subcontractor, the Engineer of Record, the Commissioning Authority (where one is engaged), and the Owner's representative.
11.1.5 Deficiency Report Distribution
☑ General Contractor
☐ Responsible installing subcontractor
☐ Engineer of Record
☐ Commissioning Authority (if engaged)
☐ Owner's representative
11.2 What Belongs in a Deficiency Report (vs. a Punch List)
NOTE A deficiency report identifies a performance shortfall that prevents the TAB Contractor from completing the balance to specified tolerance, and items within the TAB Contractor's own ability to correct by additional adjustment time are not deficiency-report items. (11.2.1)
11.2.2 Items that require installation work, controls programming, replacement of installed equipment, or design clarification are deficiency-report items.
NOTE Typical deficiency report subjects include missing or inaccessible balancing dampers and valves; flow-measurement stations installed without adequate upstream straight pipe; control valves stroking incorrectly or failing to close tight; VFD speed-command saturation at 100% with system still below design flow; coil performance shortfalls indicating fouling or air entrainment; outdoor airflow that cannot be brought to design without unacceptably increased fan power; and fan or pump operating points outside acceptable regions of the certified curve. (11.2.3)
11.3 Re-Balance After Correction
11.3.1 After the responsible party corrects each reported deficiency, the TAB Contractor shall re-measure the affected system or device and confirm that the corrected condition is in compliance.
11.3.2 Re-balance results shall be included in the Final TAB Report with a note indicating the original deficiency, the corrective action taken, and the post-correction measurement.
11.3.3 Where re-balance is not feasible before the Final Report (because the correction cannot be completed in the project schedule), the deficiency shall be carried as "open" in the Final Report.
12 Reports
12.1 Preliminary TAB Report (Pre-Balance Report)
12.1.1 Before mobilizing field work, the TAB Contractor shall submit a Preliminary TAB Report (also called the pre-balance report or agenda) that demonstrates the TAB Contractor has reviewed the contract documents, understands the systems to be balanced, and has identified the design values that the field work will verify.
12.1.2 The Preliminary Report shall include a list of every air-handling unit, fan, pump, coil, terminal device, and balancing device to be addressed, with the corresponding design airflow, design water flow, design pressure drop, design temperature, and design fan/pump operating point.
12.1.3 The Preliminary Report shall also include the TAB schedule, the proposed test procedures for any non-standard systems, and the final blank report forms.
12.1.4 Preliminary Report Requirement
● Yes — submit before TAB mobilization
○ No — proceed directly to field work (small projects only)
12.2 Full Field Data Records
12.2.1 During field work, the TAB Contractor shall record raw measurement data on field-data sheets at the time of measurement.
12.2.2 Field-data sheets shall be retained by the TAB Contractor for the duration of the warranty period and shall be made available to the Engineer or Commissioning Authority on request.
NOTE The Final TAB Report is a summary; the field-data sheets are the source documents. (12.2.3)
12.3 Final TAB Report
12.3.1 Final TAB Report Contents
12.3.1.1 The Final TAB Report shall be issued at the conclusion of the field work and shall include the following sections, signed and sealed by the certified TAB Supervisor:
- Cover page with project name, location, TAB Agency, TAB Supervisor's name and certification number, report date, and revision history
- Certification statement signed and sealed by the TAB Supervisor, attesting that the readings reported are the result of measurements personally taken or personally witnessed
- Project summary with a description of the systems balanced, the procedural standard followed, and any deviations from this standard authorized by the Engineer
- Instrument list with serial numbers and calibration dates
- Summary of deficiencies, with a status (corrected, open, accepted as-is) for each
- Air system reports — one section per fan or air-handling unit — including design vs. measured fan total airflow, fan static pressures, fan RPM, motor electrical, traverse data, terminal device airflows (room-by-room tabulation), outdoor airflow verification, and a fan operating point on the manufacturer's certified curve
- Hydronic system reports — one section per pump — including design vs. measured pump flow, suction and discharge pressures, TDH, pump RPM, motor electrical, coil-by-coil flow tabulation, balancing-valve final positions, and a pump operating point on the manufacturer's certified curve
- Marked-up record drawings with the locked position of every adjusted balancing device
- Sound and vibration spot-check readings, where in scope
- Appendices: instrument calibration certificates; manufacturer fan and pump curves with measured operating points plotted; raw field-data sheets as an appendix or by reference
● Bound printed copies plus searchable PDF
○ Searchable PDF only
○ Searchable PDF plus structured data export (CSV or XML) for BAS import
● Certified TAB Supervisor (NEBB-CP or AABC-TBE)
○ Certified TAB Supervisor plus Professional Engineer where required by jurisdiction
12.4 Seasonal Re-Balance Report
12.4.1 Where seasonal re-balance is included in the TAB scope, a supplementary report shall be issued covering the re-balance work performed during the opposite-season operating mode.
12.4.2 The seasonal report shall identify any adjustments made to the as-balanced condition and shall be referenced from the original Final Report.
12.4.3 Seasonal Re-Balance Scope
○ Yes — full re-balance during opposite operating season
● Yes — limited verification only (spot checks during opposite season)
○ No — single-season balance only
13 Installation
NOTE TAB is not an installation scope, but the TAB Contractor's field activities are physical operations within the building that require coordination with concurrent construction. (13.1)
13.2 Site Conditions for TAB Field Work
13.2.1 The Contractor shall provide the TAB Contractor with safe access to all equipment, dampers, balancing valves, flow stations, and pressure ports being measured.
13.2.2 Ladders, lifts, and fall-protection provisions shall be available where access is overhead.
13.2.3 Where ceiling tiles or access panels must be removed and reinstalled to access dampers and devices, the Contractor shall coordinate the removal and reinstallation with the TAB Contractor's schedule.
13.3 Marking and Locking Balancing Devices
13.3.1 When the TAB Contractor adjusts a balancing damper or balancing valve to its final set position, the position shall be locked using the device's locking feature (memory stop, lock-handle screw, or wired lock-tag) and shall be marked permanently with a tag indicating the device tag number, the final position, and the date set.
13.3.2 Adjustment of locked devices after TAB completion by any party other than the TAB Contractor or with the TAB Contractor's documented consent is not permitted, and doing so invalidates the Final TAB Report.
13.3.3 Balancing Device Lock and Mark Method
● Memory stop or position-lock feature integral to the device
○ External tag with locking wire and TAB Contractor's seal
○ Both — memory stop and external locking tag
14 Delivery, Storage, and Handling of Instruments
14.1 TAB instruments are the property of the TAB Contractor and shall be transported, stored, and handled in conformance with the instrument manufacturer's instructions to preserve calibration.
14.2 Instruments shall not be left unattended at the project site overnight unless secured in a locked enclosure.
14.3 Damaged instruments shall be removed from service and re-calibrated or repaired before further use, and the TAB Contractor shall not report readings taken with an instrument suspected of being out of calibration.
15 Warranty
15.1 TAB Workmanship Warranty
15.1.1 The TAB Contractor shall warrant the accuracy of the readings reported in the Final TAB Report for a period of one year from the date of substantial completion.
15.1.2 Where the building experiences performance issues attributable to TAB error during the warranty period, the TAB Contractor shall return to the project at no additional cost to re-measure the affected systems and to issue corrective findings.
15.1.3 Warranty Period
1 year from substantial completion
2 years from substantial completion
NOTE The TAB Contractor's warranty is a workmanship warranty on the accuracy of the measurement and reporting work, and is not a warranty of the long-term performance of the HVAC systems themselves; the performance warranty rests with the installing contractors and equipment manufacturers. (15.2.1)
15.2.2 Drift in system performance over time due to filter loading, coil fouling, drift in controls calibration, building load changes, or equipment wear is not a TAB defect and is not covered by the TAB warranty.
15.3 Owner Maintenance to Preserve the As-Balanced Condition
NOTE After project closeout, the Owner's maintenance practices govern whether the as-balanced condition persists. (15.3.1)
15.3.2 Filter changes on schedule, coil cleaning at recommended intervals, BAS sensor calibration verification, and inspection of locked balancing-device positions during routine maintenance are needed to preserve the as-balanced condition.
15.3.3 The TAB Final Report is the baseline against which future re-balance or troubleshooting work is compared, and the Owner shall retain the report as a permanent record of the system as accepted.