What is Factory Acceptance Testing (FAT) and why does it matter?
Factory Acceptance Testing (FAT) is a formal process conducted at the manufacturer’s facility before an air handling unit (AHU) is delivered to site. Its purpose is to confirm that the unit has been constructed to the agreed specification, performs correctly under controlled test conditions, and meets all relevant technical and regulatory standards.
FAT matters because it reduces the risk of onsite delays, identifies faults early, and provides assurance to both clients and consultants. For the manufacturer, it represents a critical quality control milestone. For the customer, it serves as independent verification that the product ordered is the product delivered.
In regulated sectors such as healthcare, pharmaceuticals, and cleanrooms, FAT is often a contractual or compliance requirement. In all cases, it provides an opportunity to verify documentation, operational readiness, and build quality before logistics and installation complexity are introduced.
What does a typical FAT procedure include?
A FAT procedure is a structured series of inspections, tests, and verifications that demonstrate performance and compliance across mechanical, electrical, and functional domains.
Initial visual inspections assess the unit for structural integrity, panel alignment, paint finish, and correct assembly. Technicians confirm that components match the general arrangement drawings and that access panels, hinges, dampers, and supports are correctly installed.
Dimensional verification confirms that the unit conforms to the agreed footprint, installation constraints, and access clearances. This prevents costly site rework due to oversizing or interference.
Electrical testing is conducted under the wiring regulations defined in BS 7671. It includes confirmation of correct terminations, functioning of interlocks, motor starter operation, and control logic sequencing. Power is applied to simulate full operating conditions.
Performance testing assesses airflow and static pressure delivery under simulated duct resistance. Fan curves are compared against project requirements, and deviations must fall within accepted tolerances — usually ±5% for airflow and ±10% for pressure.
Casing performance is evaluated to BS EN 1886 standards. This includes mechanical strength classification (D1–D3), air leakage classes (L1–L3), and thermal transmittance values. Leakage testing uses internal pressurisation and manometer readings to quantify losses.
Noise output is measured using sound power level testing, typically to ISO 3744 or ISO 3746. These standards define the test conditions and instrumentation setup. Noise-critical applications, such as hospitals or universities, often require this data at the point of FAT.
Vibration testing is carried out to ISO 14694, confirming that the fan and drive assemblies remain within acceptable vibration thresholds. Excessive vibration can lead to long-term mechanical failure or energy inefficiency.
Finally, documentation is reviewed to ensure the O&M manual, wiring diagrams, calibration certificates, product datasheets, and test records are complete, accurate, and compliant.
Who typically witnesses a FAT and why is that important?
FATs are usually witnessed by the client or a nominated representative — often a consulting engineer, M&E contractor, commissioning manager, or project quality lead. The purpose of this witness is not just to observe, but to validate the results and confirm that the AHU meets the stated project requirements.
This witness role is especially critical for NHS and pharmaceutical projects, where HTM 03‑01 compliance or GMP validation protocols demand independently verifiable evidence. FAT witnessing improves communication, reduces ambiguity, and facilitates smoother commissioning on site.
At Mansfield Pollard, we offer both in-person and remote FAT witnessing, with full test packs prepared for approval and sign-off. This allows multiple stakeholders to confirm quality without adding logistical burden.
What are the benefits of FAT / Factory Acceptance Testing?
The benefits of FAT extend far beyond quality control. At the highest level, FAT helps eliminate risk, increase confidence, and improve project delivery efficiency.
By identifying issues in a factory setting, FAT allows corrective action before transport and installation. This prevents delays, avoids cost overruns, and ensures system integration is not compromised by hidden defects.
FAT also improves documentation standards. A complete FAT pack includes control logic verifications, airflow measurements, leakage tests, and wiring checks — all of which support commissioning and long-term maintenance planning.
From an assurance perspective, FAT reinforces trust. Clients gain confidence that the equipment is technically sound. Consultants are reassured that specifications have been met. Site teams are empowered with validated handover materials.
Ultimately, FAT is about validation, accountability, and reliability — all of which are critical on complex building services projects.
What is Site Acceptance Testing (SAT) and how is it different?
While FAT occurs at the factory, Site Acceptance Testing (SAT) takes place once the AHU has been delivered and installed. Its purpose is to confirm that the unit integrates correctly with the building, operates under live conditions, and performs in accordance with both specification and site-specific parameters.
SAT includes re-verification of airflow, temperature control, noise levels, and system responsiveness — all in the context of connected ductwork, building management systems (BMS), and final service connections.
Visual checks confirm that no damage has occurred in transit and that all components remain securely fixed and aligned. Electrical checks confirm correct site terminations and that control interfaces respond as expected.
Functionality tests are repeated to ensure the unit meets its design duty. This includes assessing how the AHU modulates in response to BMS commands, environmental feedback, or occupancy changes.
Unlike FAT, SAT validates integration. It ensures that sensors, actuators, valves, and fans all respond correctly within the site ecosystem. It also verifies final commissioning — confirming that settings, modes, alarms, and sequences match the project narrative.
The most common AHU performance FAT tests undertaken trend towards:
1 – Casing Leakage Test:
Proving that the unit achieves the specified leakage rate, classified in accordance with EN 1886. (listed as a requirement within HTM 03-01 part A)
2 – Air Volumetric Proving Test:
Demonstrates that the unit provides the specified duty at an agreed simulated operating point. At the most basic level this will usually be the reference (or validation) load conditions defined in EN 167983-3. or if replicating the target environment then at functional load conditions.
3 – Pressure Drop Test:
The pressure drop test verifies that the pressure drops across various components, such as filters and coils, are within the design specifications. Pressure drop is measured using manometers or differential pressure sensors
4 – Fan Proving:
Provides evidence of fan design static pressure / Power consumption / Running speed and SFP at Reference (or validation) load conditions defined in EN 16798-3.
5 – Casing Mechanical Strength:
Demonstrates that structurally the casing is not deformed in operation beyond the customer design specified classified in accordance with EN 1886.
6 – Acoustic Testing:
Confirms that the unit meets the required acoustic specification for casing breakout as defined in BS EN ISO 3744:2010
Are both FAT and SAT essential?
Neither is essential, but both FAT and SAT perform different roles but are equally important. FAT validates that the AHU has been manufactured correctly and functions independently. SAT confirms that it performs as required once installed in its final environment.
Together, they form a closed loop of quality assurance. FAT ensures the manufacturer delivers what was promised. SAT ensures the system behaves correctly under real-world conditions.
Neglecting either process introduces risk. Without FAT, defects may go unnoticed until costly site issues arise. Without SAT, even a perfect AHU may fail to deliver because of installation, commissioning, or integration problems.
Best practice is to view FAT and SAT as complementary, not optional: especially on projects with high specification, tight timelines, or regulatory oversight.
What standards and regulations apply to FAT and SAT?
A range of British, European, and international standards guide the FAT and SAT processes:
- BS EN 1886 — Defines mechanical performance of AHUs, including casing strength, leakage, and thermal performance.
- BS EN 13053 — Covers performance ratings for ventilation components such as fans, filters, coils, and energy recovery systems.
- ISO 3744 / ISO 3746 — Standards for acoustic sound power testing.
- ISO 14694 — Defines acceptable vibration limits and fan balance conditions.
- BS 7671 — UK wiring regulations, essential for electrical safety testing.
- HTM 03‑01 — Department of Health guidance for ventilation in healthcare premises, detailing commissioning and compliance requirements.
- IQ/OQ Protocols — Installation Qualification / Operational Qualification standards relevant to pharmaceutical and GMP environments.
What standards and regulations apply to FAT and SAT?
If the AHU fails FAT, the responsibility lies with the manufacturer to resolve the issue before shipment. Remedial work may include hardware replacement, wiring correction, software reprogramming, or mechanical adjustment. Once complete, the FAT is repeated and re-witnessed.
If SAT failure occurs, root cause analysis is required. Common causes include wiring errors, incorrect control sequences, duct leakage, or sensor misplacement. These are usually resolved by the installation or commissioning team, often in conjunction with the manufacturer.
In both cases, all corrections must be documented. Final project sign-off should only proceed when both FAT and SAT confirm full compliance with specification and operational expectations.
How does Mansfield Pollard support the FAT and SAT process?
Mansfield Pollard delivers a full FAT and SAT support service. Every unit is built and tested in accordance with the agreed specification. Our FAT process includes all required airflow, leakage, control, and acoustic testing — with optional enhancements for healthcare, pharmaceutical, and low-noise projects.
FAT sessions can be conducted in person or remotely. Full test packs are provided for witness approval, and documentation is aligned to project standards including HTM 03‑01 and BS EN specifications.
On site, we support SAT through commissioning validation, documentation review, and BMS integration checks. Our team works directly with contractors and consultants to resolve issues quickly and maintain compliance throughout.
For clients operating in regulated sectors, we can adapt our FAT and SAT procedures to fit with IQ/OQ validation frameworks, ensuring a seamless experience from factory floor to final handover.
