+---
+title: Variable Air Volume Terminal Units
+category: Mechanical / Air Distribution
+toc_depth: 3
+description: >
+ When to use: zone-level pressure-independent VAV terminal units (VAV boxes) metering primary air from a central variable-air-volume air handler in commercial, institutional, and healthcare HVAC systems — single-duct cooling-only and reheat units, series and parallel fan-powered terminal units, and dual-duct VAV mixing boxes, including casing, modulating damper and actuator, averaging airflow sensor, reheat coil, ECM fan, and integral DDC/BACnet controller. Emphasizes ASHRAE 90.1 reheat and minimum-airflow compliance, static pressure reset participation, ASHRAE Guideline 36 control sequences, and ECM motor requirements.
+ Not intended for: room-boundary diffusers, grilles, and slot outlets (see [[sync/hvac-air-distribution-devices]]); central air handling units that generate the primary air (see [[sync/air-handling-units]]); upstream and downstream ductwork and fittings (see [[sync/duct-accessories]]); the broad air-terminal family including constant-volume reheat, induction, and the general construction/QA baseline (see [[sync/air-terminal-units]]); in-line sound attenuators (see [[sync/hvac-sound-attenuators]]); 100%-outdoor-air makeup units (see [[sync/makeup-air-units]]); fan coils and chilled beams; laboratory venturi airflow control valves for critical pressurization; reheat coil hydronic supply and return piping (see [[sync/hydronic-piping]]); fan-powered cooling-coil condensate drainage (see [[sync/condensate-drainage-piping]]); and AHU fan VFDs (see [[sync/hvac-variable-frequency-drives]]).
+---
+
+# Scope {toc}
+
+## This standard covers factory-fabricated variable air volume (VAV) terminal units serving as the primary zone-level airflow control device in central VAV air systems.
+
+### This standard governs single-duct pressure-independent VAV units (cooling-only and with reheat), parallel fan-powered terminal units, series fan-powered terminal units, and dual-duct VAV units. {note}
+
+### The unit assembly covered here comprises the galvanized-steel casing, the modulating primary-air damper and actuator, the multi-point averaging airflow sensor, the acoustic liner, the hydronic or electric reheat coil, the fan and motor assembly on fan-powered types, the integral or remote DDC controller, and the BACnet network interface. {note}
+
+### This standard is deliberately VAV-specific and complementary to [[sync/air-terminal-units]], which is the broad air-terminal family standard. {note}
+
+### The broad family standard carries the general casing construction, materials, and baseline quality-assurance requirements common to all air terminals; this standard goes deeper on the VAV-specific topics: pressure independence, ASHRAE 90.1 Section 6.5.2 reheat and minimum-airflow compliance, static pressure reset participation, ASHRAE Guideline 36 control sequences, and ECM fan motor requirements. {note}
+
+### Where this standard and [[sync/air-terminal-units]] both address a topic, the more stringent or more specific requirement shall govern.
+
+### VAV terminal units shall be selected, furnished, and installed in accordance with this standard, the contract drawings, and the equipment schedule.
+
+## Applications
+
+### This standard applies to new construction and replacement-in-kind in office buildings, schools, hospitals, laboratories, and similar occupancies where a central air handler delivers conditioned primary air above 0.5 in. w.g. static pressure to a distributed duct system with individual zone temperature control. {note}
+
+### The energy-code context is ASHRAE 90.1 Section 6 (VAV reheat limits, minimum airflow setpoints, fan power, and static pressure reset) and ASHRAE 62.1 (minimum part-load ventilation by demand-controlled ventilation or fixed minimums). {note}
+
+```datasheet
+label: VAV terminal unit type
+type: radio
+options:
+ - Single-duct cooling-only (no reheat)
+ - Single-duct with hydronic reheat
+ - Single-duct with electric reheat
+ - Parallel fan-powered (PFPTU)
+ - Series fan-powered (SFPTU)
+ - Dual-duct VAV (mixing box)
+default: Single-duct with hydronic reheat
+```
+
+## Exclusions
+
+### Room-boundary outlets — diffusers, grilles, registers, and linear slot outlets — are excluded and are covered by [[sync/hvac-air-distribution-devices]]. {note}
+
+### The central air handling unit that generates and distributes the primary air stream is excluded and is covered by [[sync/air-handling-units]]. {note}
+
+### Ductwork and fittings upstream of the inlet collar and downstream of the outlet collar are excluded and are covered by [[sync/duct-accessories]] and the broader ductwork standard. {note}
+
+### Constant-volume reheat units, dual-duct mixing boxes in non-VAV service, and induction units are excluded and are covered by [[sync/air-terminal-units]]. {note}
+
+### Fan coil units and chilled beams that recirculate room air rather than meter central primary air are excluded. {note}
+
+### Laboratory venturi-style airflow control valves used for critical pressurization, such as fume hood face-velocity control, are excluded. {note}
+
+### Makeup air units that supply 100% outdoor air without zone-level damper metering are excluded and are covered by [[sync/makeup-air-units]]. {note}
+
+### In-line sound attenuators installed in ductwork upstream of the terminal unit are excluded and are covered by [[sync/hvac-sound-attenuators]]. {note}
+
+### Hydronic piping serving the reheat coil and condensate drainage from fan-powered cooling coils are excluded and are covered by [[sync/hydronic-piping]] and [[sync/condensate-drainage-piping]] respectively. {note}
+
+### Variable frequency drives on the central air-handler fan are excluded and are covered by [[sync/hvac-variable-frequency-drives]]. {note}
+
+# Referenced Standards {toc}
+
+## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
+
+## Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+
+| Standard | Title |
+|----------|-------|
+| ANSI/AHRI 880-2017 (R2023) | Performance Rating of Air Terminals |
+| ANSI/AHRI 885-2008 (R2021) | Procedure for Estimating Occupied Space Sound Levels in the Application of Air Terminals and Air Outlets |
+| ANSI/ASHRAE 130-2016 | Methods of Testing Air Terminal Units |
+| ANSI/ASHRAE/IES 90.1-2022 | Energy Standard for Buildings Except Low-Rise Residential Buildings |
+| ANSI/ASHRAE 62.1-2022 | Ventilation and Acceptable Indoor Air Quality |
+| ASHRAE Guideline 36-2021 | High-Performance Sequences of Operation for HVAC Systems |
+| NFPA 90A-2024 | Standard for the Installation of Air-Conditioning and Ventilating Systems |
+| NFPA 70 (NEC) | National Electrical Code (Article 424, Fixed Electric Space-Heating Equipment) |
+| UL 60335-2-40 | Safety — Electrically Operated Heat Pumps, Air-Conditioners, and Dehumidifiers |
+| UL 181-2019 | Factory-Made Air Ducts and Air Connectors |
+| ASTM C1071-16 | Fibrous Glass Duct Lining Insulation (Thermal and Sound Absorbing Material) |
+| ASTM E84-24 | Surface Burning Characteristics of Building Materials |
+| SMACNA HVAC Duct Construction Standards (4th ed., 2021) | HVAC Duct Construction Standards — Metal and Flexible |
+| ANSI/NEMA MG 1-2021 | Motors and Generators |
+| ANSI/ASHRAE/ACCA 180-2012 | Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems |
+
+## ASHRAE Guideline 36 is a consensus best-practice document, not a mandatory code, but it is the preferred basis for VAV terminal unit control sequences under this standard. {note}
+
+# Submittals {toc}
+
+## Action Submittals
+
+### The Contractor shall submit the following action submittals for review before fabrication:
+
+- Product data for each VAV terminal unit type, including AHRI 880 certified ratings for primary airflow, casing leakage, pressure drop, and sound power
+- Shop drawings showing casing dimensions, inlet and outlet sizes, service clearances, access locations, and mounting details
+- Equipment schedule confirming maximum and minimum primary airflow setpoints, inlet size, inlet velocity, and reheat capacity for each tagged unit
+- Reheat coil performance data: hydronic capacity at scheduled entering water temperature and flow, or electric kW, stages, and sheath material
+- Fan and ECM motor data for fan-powered units, including watts per CFM at design airflow
+- DDC controller data sheets, BACnet protocol and profile, point list, and object mapping
+- Acoustic performance: AHRI 885 occupied-space NC calculation for each representative zone at design conditions
+
+```datasheet
+label: Action submittals required
+type: checkbox
+options:
+ - AHRI 880 certified product data
+ - Shop drawings with service clearances
+ - Airflow setpoint schedule (max/min/velocity)
+ - Reheat coil performance data
+ - ECM fan/motor watts-per-CFM data
+ - DDC controller data and BACnet point list
+ - AHRI 885 NC acoustic calculation
+default:
+ - AHRI 880 certified product data
+ - Shop drawings with service clearances
+ - Airflow setpoint schedule (max/min/velocity)
+ - DDC controller data and BACnet point list
+```
+
+## Informational Submittals
+
+### The Contractor shall submit the following informational submittals before delivery to the site:
+
+- NRTL listing evidence (UL 60335-2-40) for units containing electric heat, motors, or electronic controls
+- Liner material certification showing ASTM C1071 compliance and ASTM E84 flame-spread/smoke-developed indices
+- Factory flow-calibration certificate for each unit
+- Manufacturer's installation, start-up, and balancing instructions
+
+```datasheet
+label: Informational submittals required
+type: checkbox
+options:
+ - NRTL listing (UL 60335-2-40)
+ - Liner ASTM C1071 / E84 certification
+ - Factory flow-calibration certificate
+ - Installation and start-up instructions
+default:
+ - NRTL listing (UL 60335-2-40)
+ - Liner ASTM C1071 / E84 certification
+ - Factory flow-calibration certificate
+```
+
+## Closeout Submittals
+
+### The Contractor shall submit the following closeout submittals before substantial completion:
+
+- Operation and maintenance manuals covering damper, actuator, reheat coil, fan, and controller service
+- As-built BACnet point list and final control sequence documentation
+- Field commissioning and air-balance reports showing achieved maximum and minimum airflow at each unit
+- Warranty documentation
+
+```datasheet
+label: Closeout submittals required
+type: checkbox
+options:
+ - O&M manuals
+ - As-built BACnet point list and sequences
+ - Commissioning and air-balance reports
+ - Warranty documentation
+default:
+ - O&M manuals
+ - As-built BACnet point list and sequences
+ - Commissioning and air-balance reports
+ - Warranty documentation
+```
+
+# Quality Assurance {toc}
+
+## Certification
+
+### Every VAV terminal unit furnished under this standard shall be certified to ANSI/AHRI 880 and shall bear the AHRI certification mark.
+
+### AHRI 880 certified values for primary airflow, casing leakage, pressure drop, and sound power shall be the basis of selection; manufacturer's uncertified ratings shall not be substituted. {note}
+
+### Sound performance shall be projected to the occupied space using ANSI/AHRI 885 before the unit selection is finalized.
+
+### Units containing electric heating elements, motors, or electronically controlled components shall be listed and labeled by a Nationally Recognized Testing Laboratory to UL 60335-2-40.
+
+## Manufacturer Qualifications
+
+### The manufacturer shall have produced AHRI 880 certified VAV terminal units of the specified types for not less than five years.
+
+### All VAV terminal units on the project shall be the product of a single manufacturer.
+
+### Mixing controller makes or models across a single project, without a confirmed BACnet object map for each, drives integration RFIs and programming change orders during controls startup; standardizing on one make avoids this and ensures consistent controller make, BACnet object mapping, and service parts. {note}
+
+## Source Quality Control
+
+### Each unit shall be flow-calibrated at the factory across its specified airflow range per ANSI/ASHRAE 130.
+
+### Casing leakage shall be verified at the rated close-off pressure as part of the AHRI 880 certification program.
+
+# Environmental and Service Conditions {toc}
+
+## Operating Conditions
+
+### VAV terminal units shall be suitable for indoor installation in a conditioned ceiling plenum or above an accessible ceiling, not exposed to weather. {note}
+
+### Units shall operate with primary air supplied by the central air handler at static pressure above 0.5 in. w.g. and across the inlet static pressure range scheduled for the project. {note}
+
+### The casing and components shall be rated for continuous operation at the supply-air temperature range delivered by the central system, including morning warm-up.
+
+```datasheet
+label: Inlet static pressure operating range
+type: range
+unit: in. w.g.
+min: 0.5
+max: 3.0
+step: 0.1
+```
+
+```datasheet
+label: Damper close-off pressure rating
+type: select
+unit: in. w.g.
+options:
+ - "4"
+ - "5"
+ - "6"
+default: "4"
+```
+
+## Pressure Independence
+
+### VAV terminal units shall be pressure-independent, with an integral averaging airflow sensor and DDC controller that maintain the commanded airflow setpoint regardless of variations in inlet static pressure.
+
+### Pressure-dependent units shall not be used in a central VAV system.
+
+### A pressure-dependent unit reads damper position rather than airflow, so it delivers an incorrect, drifting flow whenever system static pressure changes — which in a VAV system is continuous; only pressure-independent control holds the ventilation and load setpoints the design relies on. {note}
+
+```datasheet
+label: Airflow control mode
+type: radio
+options:
+ - Pressure-independent (integral airflow sensor)
+ - Pressure-dependent (legacy low-pressure only)
+default: Pressure-independent (integral airflow sensor)
+```
+
+# Unit Sizing and Airflow {toc}
+
+## Inlet Sizing
+
+### The unit frame size shall be selected from the maximum primary airflow and inlet velocity, not from the connecting duct size. {note}
+
+### Sizing the inlet to match the duct rather than the airflow oversizes the inlet, which drives the airflow sensor below its accurate range at minimum setpoint and produces poor ventilation control and unstable DDC hunting; size to velocity first. {note}
+
+### The design inlet velocity shall not exceed 1,200 FPM, and shall not exceed 900 FPM for units whose minimum airflow setpoint is 50% or more of maximum, per ASHRAE 90.1.
+
+```datasheet
+label: Primary inlet diameter (round)
+type: select
+unit: in.
+options:
+ - "4"
+ - "5"
+ - "6"
+ - "7"
+ - "8"
+ - "9"
+ - "10"
+ - "12"
+ - "14"
+ - "16"
+ - "18"
+ - "20"
+default: "8"
+```
+
+```datasheet
+label: Maximum primary airflow (design cooling)
+type: range
+unit: CFM
+min: 40
+max: 7000
+step: 10
+```
+
+```datasheet
+label: Design inlet velocity (maximum)
+type: range
+unit: FPM
+min: 600
+max: 1200
+step: 25
+```
+
+## Minimum Airflow Setpoint
+
+### The minimum primary airflow setpoint shall be the greatest of the ASHRAE 62.1 part-load ventilation requirement, the applicable ASHRAE 90.1 Section 6.5.2.1 reheat minimum, and the manufacturer's published low-flow accuracy limit.
+
+### The minimum setpoint shall not be set below approximately 10% to 15% of maximum without verifying the manufacturer's published low-flow accuracy data at that flow; setting a minimum below the sensor's reliable range produces unstable readings and ventilation faults that surface only at commissioning. {note}
+
+```datasheet
+label: Minimum primary airflow setpoint (% of maximum)
+type: range
+unit: "%"
+min: 10
+max: 50
+step: 5
+```
+
+## ASHRAE 90.1 Reheat Compliance
+
+### Where reheat is provided, the minimum primary airflow setpoint at which reheat is permitted shall comply with ASHRAE 90.1-2022 Section 6.5.2.1.
+
+### The permitted minimum for reheat shall be the greater of 20% of the design zone supply airflow, 0.4 CFM/ft² of conditioned floor area, or the minimum required by ASHRAE 62.1.
+
+### The design documents shall confirm and record the governing reheat minimum for each zone before the setpoints are programmed. {note}
+
+### Specifying a minimum setpoint lower than ASHRAE 90.1 permits is a code violation that is frequently not caught until commissioning or energy inspection; confirming compliance at design avoids rework. {note}
+
+```datasheet
+label: ASHRAE 90.1 reheat minimum basis
+type: radio
+options:
+ - 20% of design zone supply airflow
+ - 0.4 CFM/ft² of conditioned floor area
+ - ASHRAE 62.1 minimum ventilation
+default: 20% of design zone supply airflow
+```
+
+```datasheet
+label: AHRI 880 primary airflow accuracy
+type: radio
+options:
+ - "±10% of setpoint (standard)"
+ - "±5% of setpoint (labs / critical spaces)"
+default: "±10% of setpoint (standard)"
+```
+
+# Casing and Acoustic Construction {toc}
+
+## Casing
+
+### The casing shall be galvanized steel of not less than 20 gauge for the body and damper, with reinforced corners and a static pressure class consistent with the supply-air pressure class of the system per the SMACNA HVAC Duct Construction Standards.
+
+### Inlet and outlet collars shall be round or rectangular as scheduled and shall be sized to suit the connecting ductwork.
+
+### Casing air leakage at the rated close-off pressure shall not exceed the AHRI 880 leakage class specified below.
+
+### The casing static pressure class shall be not less than 2 in. w.g.
+
+```datasheet
+label: Casing gauge (galvanized steel)
+type: radio
+options:
+ - 20 gauge (standard)
+ - 22 gauge
+default: 20 gauge (standard)
+```
+
+```datasheet
+label: AHRI 880 casing leakage class
+type: radio
+options:
+ - "Class A (≤ 2% of max airflow)"
+ - "Class B (≤ 5% of max airflow)"
+default: "Class A (≤ 2% of max airflow)"
+```
+
+```datasheet
+label: Casing cross-section
+type: radio
+options:
+ - Rectangular (standard)
+ - Round
+ - Low-profile flat-oval (shallow plenum)
+default: Rectangular (standard)
+```
+
+## Acoustic Liner
+
+### The acoustic liner shall be UL 181 listed so that it will not delaminate and enter the airstream, and shall comply with ASTM C1071. {note}
+
+### The liner shall be UL 181 listed and shall comply with ASTM C1071.
+
+### The liner material shall achieve a flame-spread index not greater than 25 and a smoke-developed index not greater than 50 per ASTM E84, as required by NFPA 90A.
+
+### Where the project is a healthcare, cleanroom, or food-service application, the liner shall be a double-wall perforated metal inner liner rather than exposed fibrous glass. {note}
+
+### Healthcare and similar applications shall use a double-wall perforated-metal liner to prevent fiber shedding into the airstream.
+
+```datasheet
+label: Acoustic liner construction
+type: radio
+options:
+ - 1 in. fibrous glass at 1.5 lb/ft³ (standard)
+ - 1.5 in. fibrous glass (higher attenuation)
+ - Double-wall perforated steel (healthcare/cleanroom)
+default: 1 in. fibrous glass at 1.5 lb/ft³ (standard)
+```
+
+## Acoustic Performance
+
+### The occupied-space sound level shall be projected per ANSI/AHRI 885 from the AHRI 880 sound power data at design conditions, accounting for both the radiated and the discharge sound paths.
+
+### The unit and liner selection shall meet the NC target scheduled for the zone.
+
+### The controlling sound path — radiated through the casing or discharged through the outlet — shall be identified for each critical zone, and the liner thickness and density selected accordingly. {note}
+
+### Skipping the AHRI 885 calculation and selecting liner by habit is the most common cause of post-occupancy noise complaints; run the calculation per zone before finalizing. {note}
+
+```datasheet
+label: Occupied-space NC target
+type: select
+options:
+ - "NC 20-30 (conference rooms)"
+ - "NC 25-35 (open office)"
+ - "NC 30-40 (corridors)"
+default: "NC 25-35 (open office)"
+```
+
+# Reheat Coils {toc}
+
+## General
+
+### Where the zone requires heating, the reheat coil type shall be selected from hydronic or electric based on the availability and cost-effectiveness of hot water distribution at the unit. {note}
+
+### Interior and perimeter zones with hot water available are most economically served by a one- or two-row hydronic coil; small isolated zones without practical hot water distribution are served by staged or SCR electric reheat. {note}
+
+```datasheet
+label: Reheat coil type
+type: radio
+options:
+ - None (cooling-only)
+ - Hydronic (hot water)
+ - Electric (staged or SCR)
+default: Hydronic (hot water)
+```
+
+## Hydronic Reheat Coils
+
+### The hydronic reheat coil entering water temperature scheduled for the unit shall match the hot water distribution system design temperature. {note}
+
+### A reheat coil selected for an entering water temperature that does not match the building hydronic system delivers inadequate capacity that cannot be corrected without replacing the coil; coordinate the temperature with the hydronic design before selection. {note}
+
+### The coil shall be selected to deliver the scheduled heating capacity at the scheduled entering water temperature and flow rate.
+
+### Coil tubes and fins shall be copper tubes with aluminum or copper fins, mechanically bonded.
+
+### The coil waterside pressure drop shall not exceed the value scheduled for the unit.
+
+### The reheat control valve shall be selected for the scheduled Cv and shall be rated for close-off against the system pump head.
+
+### Hydronic supply, return, and balancing for the reheat coil are provided under [[sync/hydronic-piping]] and are not part of this standard.
+
+```datasheet
+label: Hydronic coil rows
+type: radio
+options:
+ - 1 row (perimeter heating, typical)
+ - 2 rows (higher capacity)
+default: 1 row (perimeter heating, typical)
+```
+
+```datasheet
+label: Entering water temperature (EWT)
+type: range
+unit: °F
+min: 120
+max: 180
+step: 5
+```
+
+```datasheet
+label: Leaving water temperature (LWT)
+type: range
+unit: °F
+min: 100
+max: 130
+step: 5
+```
+
+```datasheet
+label: Coil waterside pressure drop (maximum)
+type: range
+unit: ft H₂O
+min: 1
+max: 4
+step: 0.5
+```
+
+## Electric Reheat Coils
+
+### Electric reheat coils shall comply with NFPA 70 (NEC) Article 424 for fixed electric space-heating equipment.
+
+### An airflow-proving interlock shall prevent energizing the heating elements until proven airflow is established across the coil, per NEC Article 424.20.
+
+### Omitting the airflow-proving switch is both a code violation under NEC Article 424 and a fire risk, and is frequently missed when the electric heater is furnished as a field accessory. {note}
+
+### The coil shall include integral over-temperature protection with automatic and manual reset thermal cutouts.
+
+### The heating element sheath shall be of the material scheduled for the application.
+
+### Branch-circuit conductors and overcurrent protection shall be sized per NEC Article 424 for the scheduled total kW.
+
+```datasheet
+label: Electric reheat total capacity
+type: range
+unit: kW
+min: 0.5
+max: 10
+step: 0.5
+```
+
+```datasheet
+label: Electric reheat control
+type: radio
+options:
+ - 2 stages
+ - 3 stages
+ - SCR modulating
+default: 2 stages
+```
+
+# Fan-Powered Terminal Units {toc}
+
+## Fan-Powered Type Selection
+
+### The fan-powered terminal unit type — series or parallel — shall be selected to match the zone application, not treated as interchangeable. {note}
+
+### A series unit runs its fan continuously and delivers a constant total airflow to the space regardless of primary airflow, which suits high-ceiling, high-air-change, or mixed-occupancy zones; a parallel unit runs its fan only on a call for heat and saves fan energy, which suits standard office perimeter zones. Selecting the wrong type for the application creates comfort complaints. {note}
+
+```datasheet
+label: Fan-powered configuration
+type: radio
+options:
+ - Series (SFPTU, constant volume to space)
+ - Parallel (PFPTU, fan on heating only)
+default: Parallel (PFPTU, fan on heating only)
+```
+
+## Fan Motors
+
+### Fan-powered VAV terminal units shall use electronically commutated motors (ECM); permanent split capacitor (PSC) motors shall not be used.
+
+### ASHRAE 90.1 mandates ECM motors for fan-powered VAV units; a PSC unit specified in error will fail plan check or commissioning. {note}
+
+### The fan motor power shall not exceed 0.5 W/CFM at design airflow, per ASHRAE 90.1 Section 6.5.3.1.1.
+
+### The fan and motor shall comply with the applicable provisions of ANSI/NEMA MG 1.
+
+### The fan airflow shall be set to deliver the scheduled total airflow and induction ratio for the unit.
+
+```datasheet
+label: Fan motor type
+type: radio
+options:
+ - Electronically commutated (ECM) — required by 90.1
+default: Electronically commutated (ECM) — required by 90.1
+```
+
+```datasheet
+label: Fan motor power limit
+type: range
+unit: W/CFM
+min: 0.3
+max: 0.5
+step: 0.05
+```
+
+### Where a fan-powered unit includes a cooling coil, a condensate drain pan shall be provided; the condensate drain piping is provided under [[sync/condensate-drainage-piping]]. {note}
+
+# Dual-Duct VAV Units {toc}
+
+## Dual-Duct Mixing
+
+### Dual-duct VAV units shall accept independent hot-deck and cold-deck primary air streams and blend them with separate pressure-independent damper control to maintain the zone setpoint.
+
+### Each deck shall have its own averaging airflow sensor and damper actuator so that each inlet is independently metered and pressure-independent.
+
+### The minimum setpoint strategy for a dual-duct unit shall account for the simultaneous hot-deck and cold-deck contributions to avoid excess reheat under ASHRAE 90.1. {note}
+
+### Applying a single-duct minimum-setpoint strategy to a dual-duct unit understates the combined airflow and produces simultaneous heating and cooling that violates the ASHRAE 90.1 reheat intent; set the deck minimums for the blended condition. {note}
+
+# Controls and BACnet Integration {toc}
+
+## DDC Controller
+
+### Each VAV terminal unit shall be furnished with a DDC controller, either factory-integral or field-mounted as scheduled, capable of standalone occupied and unoccupied scheduling.
+
+### The controller shall communicate on BACnet, either BACnet MS/TP or BACnet/IP as scheduled for the project network.
+
+### The controller object list shall include, at minimum, analog outputs for damper position, analog inputs for airflow and room temperature, and binary points for occupancy and fan status. {note}
+
+### The controller shall expose, at minimum, AO for damper position, AI for measured airflow and room temperature, and BI/BO for occupancy and fan status.
+
+### The BACnet protocol version and device profile shall be confirmed with the BAS integrator before the controllers are ordered.
+
+### Confirming the BACnet profile with the integrator before ordering prevents costly firmware updates or gateway additions when an ATU controller profile does not match the BAS front-end. {note}
+
+### Where a CO2 or occupancy sensor input is scheduled for demand-controlled ventilation, the controller shall accept and act on that input. {note}
+
+```datasheet
+label: DDC controller mounting
+type: radio
+options:
+ - Factory-integral
+ - Field-mounted
+default: Factory-integral
+```
+
+```datasheet
+label: BACnet communication
+type: radio
+options:
+ - BACnet MS/TP
+ - BACnet/IP
+default: BACnet MS/TP
+```
+
+```datasheet
+label: BACnet MS/TP baud rate
+type: select
+unit: bps
+options:
+ - "9600"
+ - "19200"
+ - "38400"
+ - "76800"
+default: "38400"
+```
+
+```datasheet
+label: Demand-controlled ventilation input
+type: radio
+options:
+ - None
+ - CO2 sensor input
+ - Occupancy sensor input
+default: None
+```
+
+## Control Sequences
+
+### The VAV terminal unit control sequence shall be based on ASHRAE Guideline 36-2021 unless the contract documents specify an alternative sequence.
+
+### ASHRAE Guideline 36 is the industry-consensus best-practice sequence for VAV terminal units, covering zone setpoints, morning warm-up, demand-controlled ventilation, static pressure reset, and trim-and-respond logic; it is the preferred basis here even though it is a guideline rather than a mandatory code. {note}
+
+### Each VAV terminal unit shall participate in the system static pressure reset, reporting its damper demand so the central fan static pressure can be trimmed and responded down to the lowest setpoint that satisfies all zones.
+
+### ASHRAE 90.1-2022 Section 6.5.3.3 requires VAV systems with DDC controls to reset duct static pressure based on zone demand; the terminal unit must contribute its damper demand for that reset to function. {note}
+
+```datasheet
+label: Control sequence basis
+type: radio
+options:
+ - ASHRAE Guideline 36-2021 (preferred)
+ - Manufacturer-standard sequence
+default: ASHRAE Guideline 36-2021 (preferred)
+```
+
+```datasheet
+label: Static pressure reset participation
+type: radio
+options:
+ - Trim-and-respond (damper demand reported)
+ - Fixed duct static pressure (legacy)
+default: Trim-and-respond (damper demand reported)
+```
+
+# Testing {toc}
+
+## Field Testing and Balancing
+
+### Each VAV terminal unit shall be field-commissioned and air-balanced by the testing, adjusting, and balancing agency under [[sync/testing-adjusting-and-balancing]].
+
+### The measured maximum and minimum primary airflow at each unit shall be within ±10% of the scheduled setpoints, or within ±5% for laboratory or critical applications.
+
+### The airflow-proving interlock on electric reheat coils shall be functionally verified before the coil is energized.
+
+### The control sequence and BACnet points shall be verified against the as-built point list during functional testing.
+
+```datasheet
+label: Field airflow commissioning tolerance
+type: radio
+options:
+ - "±10% of design setpoint (standard)"
+ - "±5% of design setpoint (labs / critical)"
+default: "±10% of design setpoint (standard)"
+```
+
+# Installation {toc}
+
+## Mounting and Clearance
+
+### VAV terminal units shall be installed level and supported independently of the connecting ductwork, with hangers sized for the unit operating weight.
+
+### Adequate service clearance shall be provided for access to the damper actuator, reheat coil, controller, and fan, with a ceiling access panel where the unit is above a hard ceiling.
+
+### Locating a unit in a tight plenum without access creates long-term maintenance problems and warranty claims; clearance and access shall be coordinated before installation. {note}
+
+### Unit locations shall be coordinated with the ceiling grid, light fixtures, sprinkler heads, and structure before installation. {note}
+
+### Field relocation of units after installation generates coordination RFIs and potential duct rerouting; resolve conflicts during coordination, not in the field. {note}
+
+## Connections
+
+### The primary inlet shall be connected to the upstream duct with a straight run of the length recommended by the manufacturer to maintain airflow sensor accuracy.
+
+### Outlet connections shall be made to the discharge collars or plenum as scheduled, single-outlet or multiple-outlet per the unit configuration.
+
+### Electrical connections to electric reheat coils and fan motors shall be made per NEC and the manufacturer's wiring diagrams.
+
+### Control and BACnet network wiring shall be installed under [[sync/building-automation-system]].
+
+```datasheet
+label: Outlet configuration
+type: radio
+options:
+ - Single-outlet
+ - Multiple-outlet
+ - Discharge plenum box
+default: Single-outlet
+```
+
+# Delivery, Storage, and Handling {toc}
+
+## Protection
+
+### Units shall be delivered in the manufacturer's packaging with inlet and outlet collars capped to keep the interior clean and dry.
+
+### Units shall be stored indoors, protected from weather, dust, and construction debris until installation.
+
+### Damaged casings, liners, coils, or controllers shall be repaired or replaced before installation; field-patched liner shall not be accepted.
+
+# Warranty {toc}
+
+## Warranty Coverage
+
+### The manufacturer shall warrant each VAV terminal unit against defects in materials and workmanship for not less than the period scheduled below from the date of substantial completion.
+
+### The warranty shall cover the casing, damper and actuator, airflow sensor, reheat coil, fan and ECM motor, and integral controller.
+
+```datasheet
+label: Warranty period
+type: radio
+options:
+ - 1 year
+ - 2 years
+ - 5 years
+default: 1 year
+```
+
+# Spare Parts {toc}
+
+## Recommended Spares
+
+### The Contractor shall furnish the spare parts scheduled below to support the maintenance intervals of ANSI/ASHRAE/ACCA 180.
+
+- Spare damper actuator for each unit frame size on the project
+- Spare ECM motor for each fan-powered unit frame size
+- Spare DDC controller of each type furnished
+- Manufacturer's recommended consumables for the first year of operation
+
+```datasheet
+label: Spare parts to be furnished
+type: checkbox
+options:
+ - Damper actuator (one per frame size)
+ - ECM motor (one per fan-powered frame size)
+ - DDC controller (one per type)
+ - First-year consumables
+default:
+ - Damper actuator (one per frame size)
+ - DDC controller (one per type)
+```