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A Fresh Air Unit (FAU) supports ventilation by bringing outdoor air into a building and conditioning it for use. Choosing the right supplier affects more than equipment delivery. It can shape indoor comfort, energy use, maintenance needs, and system performance over time. The stakes are practical. UNEP and the Global Alliance for Buildings and Construction reported in their 2023 Global Status Report for Buildings and Construction that buildings account for about 30% of global final energy consumption. This figure covers buildings broadly, not FAUs alone. Still, it shows why buyers should examine efficiency claims carefully. ASHRAE Standard 62.1-2022 also provides widely used ventilation guidance for many commercial buildings, though applicable requirements depend on the project and location.
A reliable FAU supplier should explain how its equipment meets the project’s airflow, filtration, control, and installation needs. Look for clear technical submittals, tested performance data, component details, warranty terms, and accessible after-sales support. Ask how the supplier verifies airflow and handles commissioning questions. Request references for comparable projects, not just attractive product photographs. A catalogue can look convincing; it proves less than many buyers hope. Reliability is measurable. Compare stated performance with independent test documentation, and check that proposed specifications match the design brief. Price matters, but so do replacement-part availability and realistic lead times. Some buyers overlook these details until the first service visit. That is worth reconsidering. This guide outlines practical checks for evaluating FAU suppliers and choosing a partner whose claims can be verified.
A reliable FAU selection starts with a clear ventilation brief, not a guessed unit size. Use the applicable edition of ASHRAE Standard 62.1 and confirm which edition local requirements reference. For each occupied zone, record floor area, expected people, and use. These inputs help determine the required outdoor-airflow rate. Small details matter.
Then check how air reaches each space. Supply airflow and outdoor airflow are not the same: a unit may move plenty of air while bringing in too little outdoor air. Account for zone air distribution, system ventilation efficiency, exhaust, and building pressure. A busy meeting room, for example, may need a different outdoor-air allowance than a quiet corridor. A first-pass estimate helps, but it can be wrong if occupancy or room use changes.
When comparing suppliers, ask for a selection that states both total supply airflow and outdoor airflow, with the assumptions shown. Request fan performance at the actual system resistance, not just a catalog maximum. Ask how dampers, filters, and controls maintain the required intake as conditions change. Review the calculation with a qualified ventilation professional, especially when zones share equipment. The supplier should explain any gap between the design target and the delivered airflow, plainly and with measurable values.
Use this planning table to define the project’s outdoor-air requirements before comparing Fresh Air Unit (FAU) suppliers. Final design must follow the locally adopted code and applicable edition of ASHRAE Standard 62.1.
| Design Dimension | What to Establish | Illustrative Data or Calculation | What to Request from the Supplier |
|---|---|---|---|
| Applicable standard and space classification | Identify the adopted ASHRAE 62.1 edition, local mechanical code, and the correct occupancy category for each zone. | For example, distinguish a general office from a conference room, classroom, or dining area; their ventilation-rate inputs may differ. | A written design basis listing the standard edition, occupancy categories, applicable code requirements, and any project-specific assumptions. |
| People outdoor-air rate (Rp) | Determine the breathing-zone outdoor-air rate per person for each occupancy category using the applicable standard table. | A commonly cited office example is 5 cfm/person (about 2.36 L/s per person). Verify the value against the adopted edition and space classification. | The design occupant count for every zone and the Rp value used, with its source and units. |
| Area outdoor-air rate (Ra) | Determine the breathing-zone outdoor-air rate per unit floor area for each occupancy category. | A commonly cited office example is 0.06 cfm/ft² (about 0.305 L/s·m²). Verify the value against the adopted edition and space classification. | The net floor area by zone and the Ra value used, with its source and units. |
| Breathing-zone outdoor airflow (Vbz) | Calculate each zone’s breathing-zone outdoor airflow using the Ventilation Rate Procedure. | Vbz = Rp × Pz + Ra × Az, where Pz is zone population and Az is zone floor area. Example: an office with 100 people and 10,000 ft² gives 5 × 100 + 0.06 × 10,000 = 1,100 cfm (about 1,869 m³/h). | A zone-by-zone calculation schedule showing inputs, equations, units, and resulting Vbz values. |
| Zone air-distribution effectiveness (Ez) | Account for how supply-air delivery affects ventilation effectiveness in each zone. | Zone outdoor airflow is calculated as Voz = Vbz / Ez. Do not assume Ez = 1.0 unless the selected system and applicable standard support that value. | The assumed Ez for each zone and the design conditions or system arrangement that justify it. |
| System outdoor-air intake | For a system serving multiple zones, calculate the required intake airflow at the system level; the intake may not equal the simple sum of zone Vbz values. | Apply the applicable ASHRAE 62.1 procedure, including system ventilation efficiency where required. Consider zone diversity and the system’s operating modes. | The system-level outdoor-air calculation, ventilation-efficiency method, design intake airflow, and any assumptions about diversity or simultaneous operation. |
| Design and operating airflow range | Define minimum, normal, maximum, and any turndown airflow requirements for the FAU. | Specify outdoor airflow in consistent units such as cfm or m³/h, and state whether values apply at the unit intake or at zone terminals. | Certified or documented airflow data at the required external static pressure, plus controls and minimum-flow limits. |
| Building pressure and exhaust coordination | Coordinate outdoor-air supply with toilet, kitchen, process, and other exhaust systems, as well as transfer air between spaces. | Document the project’s pressure strategy, including any intended neutral, positive, or negative pressure relationships. | A ventilation and exhaust balance schedule showing supply, outdoor air, exhaust, and transfer-air assumptions by area. |
| Climate and entering-air conditions | Provide the project design outdoor temperature and humidity conditions used for heating, cooling, and dehumidification selection. | Use weather design conditions appropriate to the project location and the engineer’s selected design criteria; do not select capacity from airflow alone. | Performance data at the stated entering-air conditions, including heating and cooling capacity, leaving-air conditions, and moisture-removal capability where applicable. |
| Filtration and pressure drop | Specify filtration requirements and include clean- and final-filter pressure drop in fan selection. | State the required filter efficiency or applicable project specification, along with the expected filter loading condition used for design. | Filter class or efficiency documentation, pressure-drop data, replacement dimensions, and the fan’s available airflow at the specified filter pressure drop. |
| Controls and verification | Define outdoor-air measurement, damper control, alarms, and any demand-control ventilation sequence permitted by the applicable code and standard. | Identify required sensors, control ranges, minimum ventilation settings, and the method for verifying delivered airflow during commissioning. | Control sequence, sensor accuracy information, airflow-measurement method, point list, and commissioning or start-up documentation. |
| Supplier comparison record | Compare proposals against the same airflow, pressure, climate, filtration, acoustic, electrical, and control requirements. | Record each proposal’s selected model, design airflow, external static pressure, capacity, power input, sound data, and stated deviations. | A completed compliance schedule that clearly identifies included components, exclusions, assumptions, and any variance from the project specification. |
Important: The office rates and worked example are illustrative planning values, not a substitute for the applicable ASHRAE 62.1 table or a project-specific ventilation calculation. Confirm all rates, zone effectiveness, system ventilation efficiency, and code requirements with the responsible design professional.
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