Good industrial ventilation system design is the foundation of every compliant, energy-efficient, and worker-safe industrial building in the UK. Get the design right and the system runs reliably for years, passes Building Control and HSE inspection, and keeps energy costs under control.
Get it wrong and the consequences range from poor air quality and thermal discomfort through to COSHH enforcement action and costly remedial work after handover.
This guide covers the best practice principles that contractors, M&E consultants, and facilities managers need to apply at every stage of the design process, from initial airflow assessment through to commissioning and ongoing performance verification.
What Are the Key Stages of Industrial Ventilation System Design?
Industrial ventilation system design follows a structured sequence of decisions, and skipping or rushing any stage creates problems that compound downstream. The key stages are: defining the ventilation objective and hazard level, calculating required airflow rates, selecting the appropriate system type, designing the ductwork distribution network, selecting fans and air-moving equipment, integrating controls and monitoring, and commissioning and verifying performance against the design specification.
Each stage builds directly on the one before it. A flawed airflow calculation leads to an undersized fan selection. An undersized fan leads to a system that cannot meet Part F or COSHH compliance targets under real operating conditions.
Starting with a rigorous assessment of the ventilation requirement, before any product or system type is selected, is the single most important discipline in professional industrial ventilation design.
eFans supplies fans, air terminals, and heat recovery units to contractors and M&E consultants across the UK, with free expert advice available to support ventilation system design decisions at any stage of the process.
How Do You Calculate Airflow Requirements for an Industrial Ventilation System?
Airflow requirements for industrial ventilation systems are calculated using one of three methods depending on the nature of the ventilation objective: air changes per hour (ACH), contaminant dilution calculation, or occupancy-based fresh air supply rates.
The correct method depends on whether the primary driver is general workplace air quality, thermal management, or control of specific airborne hazards under COSHH.
Air Changes Per Hour Method
The air changes per hour method calculates the required ventilation rate by multiplying the volume of the space in cubic metres by the target number of air changes required per hour for that building type. The result gives the total extract or supply volume flow rate in m³/h that the ventilation system must deliver under normal operating conditions.
Typical industrial air change rate targets range from 6 to 10 air changes per hour for general warehousing and light manufacturing, rising to 15 to 30 or more for commercial kitchens, welding shops, and process environments with significant heat or contaminant loads.
These figures are starting points rather than absolute rules, and the final design airflow should always be verified against the specific conditions of the project rather than assumed from generic guidance alone.
The ACH method is quick and widely used at the early design stage, but it does not account for system resistance, duct losses, or the actual operating point of the selected fan. Always verify that the chosen fan can achieve the required airflow rate against the calculated system static pressure, not just in free-air conditions.
Contaminant Dilution Calculation
Where the primary ventilation objective is controlling a specific airborne contaminant below its occupational exposure limit (OEL) as listed in HSE Guidance Note EH40, the required airflow rate is calculated using a dilution formula that accounts for the contaminant generation rate, the target workplace concentration, and the mixing efficiency of the ventilation system.
The dilution calculation requires accurate data on the rate at which the contaminant is generated in the workspace, which in turn requires a proper COSHH assessment rather than an assumption. For variable processes, such as intermittent welding or batch chemical handling, the peak generation rate rather than the average should be used to ensure the system provides adequate protection during worst-case operating conditions.
It is important to remember that dilution calculation is only applicable where dilution ventilation is the appropriate control strategy. For highly toxic substances or processes where workers are positioned close to the emission source, local exhaust ventilation with a capture hood is the required approach under COSHH, and airflow calculations shift to a capture velocity model rather than a dilution model.
Occupancy-Based Fresh Air Supply Rates
For industrial buildings with significant occupancy, such as large manufacturing facilities with assembly-line workers, warehouse picking operations, or industrial offices within factory buildings, the fresh air supply rate per person is an important input to the overall ventilation design.
Building Regulations Approved Document F and CIBSE Guide A both provide minimum fresh air supply rates per person for different building occupancy types.
The occupancy-based calculation is typically used alongside the ACH method rather than in isolation, with the higher of the two resulting airflow figures taken as the design requirement. This ensures the system meets both the general building ventilation requirement and the fresh air entitlement of the occupants working within it.
What Are the Best Practices for Industrial Ventilation Ductwork Design?
Ductwork design has a direct and significant impact on the performance of the ventilation system. Poorly designed ductwork creates excessive resistance, uneven airflow distribution, noise problems, and maintenance difficulties that persist for the life of the installation.
Applying best practice principles at the ductwork design stage reduces system resistance, improves airflow balance, and ensures the installed fan can deliver its rated performance under real operating conditions.
Minimising System Resistance
Every component in a ductwork system adds resistance to airflow, and the cumulative effect of those resistances determines the static pressure the fan must overcome to deliver the required flow rate.
Straight duct sections carry relatively low resistance per metre, but each bend, branch, contraction, expansion, damper, and grille adds resistance that multiplies with air velocity.
Best practice requires minimising the number of bends and fittings in the duct route, using long-radius bends rather than sharp 90-degree elbows wherever space allows, and avoiding sudden changes in duct cross-section that create turbulence and pressure loss.
Keeping duct velocities within the recommended range for the application, typically 5 to 8 m/s for industrial supply and extract mains, reduces resistance and noise while maintaining adequate transport velocity for any particulate in the airstream.
When designing for LEV systems, the duct transport velocity must be maintained above the minimum required to keep entrained particles in suspension, typically 15 to 20 m/s for heavy dust, which means duct sizing decisions involve a balance between adequate transport velocity and manageable system resistance.
Achieving Airflow Balance in Multi-Branch Systems
Multi-branch industrial ductwork systems must be designed to deliver the correct airflow to each branch without relying entirely on dampers to compensate for poor pressure balance.
The preferred approach is to design the duct system so that each branch has a similar pressure loss at its design flow rate, achieved through careful duct sizing, branch configuration, and fitting selection, with balancing dampers used only for fine adjustment rather than to compensate for large imbalances.
An unbalanced duct system delivers too much air to low-resistance branches and too little to high-resistance branches, which means parts of the building are over-ventilated at the expense of others.
In LEV systems, that imbalance can mean capture hoods furthest from the fan are starved of the airflow they need to capture contaminants effectively, creating a compliance risk that is not visible without measurement.
Computational fluid dynamics (CFD) modelling and ductwork design software such as CIBSE's approved calculation tools can be used on complex industrial systems to verify pressure balance before fabrication. On simpler systems, careful manual pressure loss calculation through each branch using the equal friction or static regain method remains the standard practice.
Duct Material Selection for Industrial Applications
Duct material selection for industrial ventilation systems depends on the nature of the airstream, the operating temperature range, the presence of moisture or chemical contamination, and the fire performance requirements of the building.
Galvanised mild steel is the standard material for most industrial ventilation ductwork, offering a practical combination of strength, workability, and durability at a competitive cost.
For corrosive or chemically contaminated airstreams, stainless steel, GRP (glass reinforced plastic), or PVC ductwork may be required to prevent degradation of the duct material over time.
In high-temperature applications such as process extract, kitchen exhaust, or fire ventilation systems, duct material must be rated for the expected operating temperature range. For general industrial mechanical ventilation in normal environments, galvanised steel to HVCA DW/144 standards remains the appropriate and widely specified choice.
How Do You Select the Right Fan for an Industrial Ventilation System?
Fan selection is one of the most consequential decisions in industrial ventilation system design, because the fan must be able to deliver the required airflow against the calculated system resistance, reliably, at an acceptable noise level, and with an energy consumption that keeps operating costs manageable over the system's life.
Selecting on flow rate alone, without checking that the fan can achieve that flow rate against the actual system static pressure, is one of the most common and costly errors in ventilation engineering.
Understanding Fan Performance Curves
Every fan has a performance curve that plots its airflow output against static pressure. At zero resistance (free air), the fan delivers its maximum flow rate. As resistance increases, flow rate falls.
The operating point of the fan in a real system is the intersection of the fan's performance curve with the system resistance curve, and that point must fall within the efficient operating range of the fan for the installation to work correctly.
Selecting a fan whose operating point falls on the steep, left-hand side of its performance curve, close to its stall point, is a common design error that leads to unstable, noisy operation and fan motor overloading.
Always verify that the selected fan's operating point sits in the stable, right-hand portion of its curve, with a reasonable margin between the design operating point and the fan's maximum pressure capability.
eFans stocks axial fans, centrifugal fans, mixed-flow fans, and inline duct fans from leading brands including Systemair, S&P, Elta, Vent-Axia, and Hydor, covering a wide range of airflow and pressure combinations for industrial ventilation applications. Technical data sheets and performance curves are available for all stocked products.
Axial vs Centrifugal Fan Selection
Axial fans are the right choice for industrial ventilation applications with low system resistance, typically below 150 Pa, where large volumes of air need to be moved at modest static pressure. They are compact, straightforward to install, and available in a wide range of sizes for both wall-mounted and duct-mounted applications.
Roof-mounted axial fans are widely used for general industrial extract in warehouses and production facilities.
Centrifugal fans generate significantly higher static pressure than axial units at the same duct diameter, making them the correct choice for systems with long duct runs, multiple bends, inline filtration, or multiple branch networks where total system resistance exceeds 150 to 200 Pa.
Centrifugal fans are also preferred for LEV systems, where the resistance of capture hoods, transport ductwork, and filtration equipment can generate total system pressures of 500 Pa or more.
Mixed-flow fans occupy a useful middle ground, offering better pressure capability than axial fans with lower noise levels than centrifugal units at the same duty. They are increasingly specified for medium-scale industrial mechanical ventilation where the system pressure is in the 150 to 300 Pa range and noise is a consideration.
eFans supplies all three fan types across the full size and output range needed for industrial system builds.
EC Motors and Energy Efficiency in Industrial Fan Selection
EC (electronically commutated) motor fans deliver significantly better energy efficiency than equivalent AC motor units, particularly when operating at partial load conditions. For industrial ventilation systems that run continuously or for long daily operating hours, the energy saving from EC motor technology is substantial and compounds over the system's operational life.
Building Regulations Part L and the Energy-Related Products Directive (ErP) have progressively tightened minimum energy efficiency requirements for fans in commercial and industrial ventilation applications.
For new-build and notifiable refurbishment projects, specifying EC motor fans is increasingly necessary to meet Part L compliance targets rather than simply desirable for cost saving. eFans stocks EC motor fans from Systemair and Elta, with free expert advice available to support compliant fan selection.
What Controls and Monitoring Systems Are Required for Industrial Ventilation?
Industrial ventilation controls range from simple on/off switching for single-point extract fans through to sophisticated building management system (BMS) integration with multiple sensors, variable speed drives, and remote monitoring capability for large multi-zone systems.
The appropriate level of control complexity depends on the scale of the system, the nature of the ventilation requirement, and the regulatory obligations that apply to the specific industrial environment.
Variable Speed Drives for Demand-Controlled Ventilation
Variable speed drives allow the fan motor speed, and therefore the airflow output, to be adjusted continuously in response to demand signals from occupancy sensors, air quality monitors, temperature sensors, or production schedule inputs.
On large industrial ventilation systems running continuous extraction, variable speed control can reduce fan energy consumption by 50 percent or more compared to fixed-speed operation, because fan power consumption reduces with the cube of fan speed reduction.
Demand-controlled ventilation also improves the effectiveness of the system by matching ventilation rate to actual need rather than running at the design maximum at all times.
In manufacturing facilities with variable shift patterns, warehouse operations with fluctuating occupancy, or process plants with intermittent contaminant-generating operations, demand control ensures the system provides adequate ventilation when it is needed while avoiding unnecessary energy consumption during quieter periods.
Air Quality Monitoring and Sensor Integration
Industrial ventilation systems serving environments where specific contaminants must be controlled, such as CO2 in heavily occupied spaces, VOCs in chemical or manufacturing environments, or particulate in dusty production areas, benefit significantly from integrated air quality monitoring.
Sensors that feed real-time contaminant concentration data to the ventilation control system enable automatic airflow adjustment that responds to actual conditions rather than a fixed time schedule or occupancy assumption.
For LEV systems and COSHH-controlled environments, continuous monitoring of capture velocity at the hood and airflow through the system provides early warning of performance degradation before it creates a compliance or safety problem. HSE guidance under HSG258 supports the use of continuous performance monitoring in LEV systems as part of a robust examination and maintenance programme.
BMS Integration for Large Industrial Sites
Large industrial buildings with multiple ventilation zones, mixed system types, and significant process ventilation requirements benefit from integrating all ventilation controls into a single building management system.
BMS integration provides centralised visibility of system performance, enables coordinated control of supply and extract to maintain building air balance, supports energy sub-metering for reporting purposes, and allows fault alarms to be captured and responded to promptly.
Specifying ventilation equipment with BMS-compatible control interfaces, including Modbus, BACnet, or LON communication protocols, is important at the equipment selection stage to avoid costly integration work later. eFans supplies fans and ventilation units from brands including Systemair and Vent-Axia that offer BMS-compatible control options.
What Does Industrial Ventilation System Commissioning Involve?
Commissioning is the process of verifying that the installed ventilation system delivers the airflow rates and pressures required by the design specification under actual operating conditions. It is not a final check at the end of a project but a structured process that identifies and resolves discrepancies between design intent and as-installed performance before the building is handed over to the client.
Airflow Measurement and Balancing
Airflow measurement at every supply and extract point in the system is the core activity of ventilation commissioning. A calibrated anemometer or flow hood is used to measure actual air velocity and flow rate at each grille, diffuser, and extract terminal, and the results are compared against the design targets for each point.
Where measured flows fall below or above design targets, balancing dampers are adjusted to bring the system into balance.
On complex multi-branch systems, achieving correct airflow balance across all terminals requires a methodical approach, working outward from the fan in a defined sequence rather than adjusting dampers arbitrarily.
BSRIA Guides BG 16 and BG 52 provide the standard commissioning methodology for UK ventilation systems, and compliance with these guides is expected on most commercial and industrial new-build projects.
LEV System Thorough Examination
For LEV systems, commissioning goes beyond general airflow measurement and must include thorough examination to HSE HSG258 standards. This involves measuring face or capture velocity at each hood, checking transport velocities in all duct sections to confirm they meet minimum entrainment velocity requirements, verifying fan performance against its characteristic curve, and checking filtration and air cleaning equipment for correct operation and condition.
The results of the commissioning thorough examination must be recorded and retained as part of the system's formal examination record, and subsequent examinations every 14 months under COSHH Regulation 9 must demonstrate that the system continues to perform to its design specification.
Any deterioration in performance identified during examination must be investigated and rectified before the system is returned to service.
Frequently Asked Questions
What regulations govern industrial ventilation system design in the UK?
Industrial ventilation system design in the UK is governed by several overlapping regulatory frameworks. The Workplace (Health, Safety and Welfare) Regulations 1992 require employers to provide effective and suitable ventilation in all workplaces.
The Control of Substances Hazardous to Health (COSHH) Regulations 2002 set specific requirements for ventilation systems that control airborne hazardous substances, including LEV design, maintenance, and testing obligations.
Building Regulations Approved Document F sets minimum ventilation rates for new-build and notifiable refurbishment projects, while Part L governs energy performance requirements including fan efficiency standards.
HSE Guidance Note EH40 lists occupational exposure limits for hundreds of substances, and HSE document HSG258 provides detailed guidance on LEV system design, use, and maintenance. CIBSE Guides A and B provide authoritative technical guidance on ventilation system design calculations and methodology.
How is system resistance calculated for industrial ductwork?
System resistance is the total static pressure the fan must overcome to deliver the required airflow through the ductwork. It is calculated by summing the pressure losses for every component in the system, including straight duct sections, bends, branches, contractions, expansions, dampers, grilles, filters, and any other inline components.
Straight duct pressure loss is calculated using the Darcy-Weisbach equation, expressed as pressure loss per metre of duct at a given velocity. Fitting losses are expressed as equivalent lengths of straight duct or as pressure loss coefficients (zeta values) applied to the dynamic pressure at that point in the system.
The calculation is carried out for every branch in the system, with the highest-resistance path, known as the index circuit, determining the total system resistance against which the fan must be selected.
What is the minimum ventilation rate required for industrial workplaces under UK regulations?
The Workplace (Health, Safety and Welfare) Regulations 1992 require that enclosed workplaces are ventilated by a sufficient quantity of fresh or purified air. The supporting Approved Code of Practice (L24) suggests a minimum fresh air supply rate of 5 to 8 litres per second per person for general sedentary workplaces, rising significantly for more physically active work or where heat or contamination loads are present.
Building Regulations Approved Document F provides specific minimum ventilation rates for different building and space types. For spaces where contaminant control is the primary driver, the minimum ventilation rate is determined by the COSHH assessment and OEL calculation rather than a fixed regulatory figure, and may be significantly higher than the general workplace minimum.
How do you prevent noise problems in industrial ventilation ductwork?
Noise in industrial ventilation systems originates from three main sources: fan-generated aerodynamic noise, mechanical noise from motor and bearing vibration, and flow-generated noise from turbulence at fittings and high-velocity duct sections.
Best practice for noise control includes selecting fans that operate in the stable, efficient portion of their performance curve rather than near stall, fitting anti-vibration mounts between the fan and its support structure, using flexible connections between the fan and ductwork to prevent vibration transmission, keeping duct air velocities within the recommended range to minimise turbulence noise, and using acoustic attenuators (silencers) in the duct run where noise transmission into occupied spaces must be limited.
Lining ductwork internally with acoustic insulation material reduces airborne sound propagation through the duct. For systems serving noise-sensitive industrial offices or meeting rooms within a factory building, detailed acoustic analysis at the design stage is the most reliable way to avoid costly remedial work after handover.
What is the design life of an industrial ventilation system, and what affects it?
A well-designed and properly maintained industrial ventilation system typically has a design life of 20 to 25 years for ductwork and 10 to 15 years for fan and motor plant, though actual service life varies considerably depending on the operating environment and maintenance regime.
Factors that shorten system life include operating in contaminated or chemically aggressive airstreams without appropriate material specification, inadequate maintenance leading to dust and contamination build-up in ductwork and on fan impellers, running fans continuously outside their efficient operating range, and failure to replace filters and clean heat exchanger surfaces on MVHR units.
Regular planned preventative maintenance, including annual fan and motor inspection, periodic ductwork cleaning in accordance with BSRIA BG 26 guidance, and prompt response to performance deterioration identified during commissioning checks, is the most effective way to maximise system service life and protect the capital investment in the ventilation installation.