Industrial Ventilation & Make-Up Air Design in Ontario

Industrial exhaust does not work in isolation. Every cubic foot removed must be replaced, conditioned and introduced without defeating source capture, creating uncontrolled negative pressure or disrupting the process.

When Ventilation Becomes an Engineering Project

An industrial ventilation problem often first appears as a complaint: a hot production area, odour travelling into offices, a door that is difficult to open, condensation near an exterior wall, visible dust outside a capture point, or a process that cannot run at full output without affecting the rest of the building. The root cause may not be the fan alone.

A new process exhaust system changes the facility's air balance. A larger fan can pull the building negative, increase winter infiltration, interfere with combustion equipment, draw contaminants across occupied areas or reduce the performance of another exhaust system. Conversely, make-up air introduced with poor temperature, velocity or location can disrupt the capture envelope it was intended to support.

Engineering becomes especially valuable when a facility adds production equipment, modifies a process, expands operating hours, installs a dust collector or spray process, replaces an exhaust fan, adds a make-up air unit, struggles with heat or pressure, or must develop permit and construction documents from incomplete records.

General Ventilation vs. Local Exhaust

General ventilation supplies and removes air across a room or building. It can help manage background heat, odours and airborne concentrations where the process and risk assessment support that strategy. Local exhaust ventilation places the capture point close to the source so material is controlled before it spreads through the space.

The correct approach depends on the process, emission characteristics, toxicity or hazard, generation rate, worker position, cross-drafts, enclosure possibilities, operating cycle and maintenance needs. A canopy hood over a hot process behaves differently from a partial enclosure, slot hood, downdraft table or machine connection. Hood shape and placement are part of the engineering—not decorative sheet metal around a duct.

A high exhaust rate cannot rescue a poor capture geometry indefinitely. Controlling the source with the least practical airflow is often more effective, more energy-efficient and easier to balance.

Exhaust, Make-Up Air and Building Pressure

Ontario's Industrial Establishments regulation requires replacement air for mechanically exhausted air and sets conditions for how that air is heated, kept free of hazardous contamination and introduced. In practical design terms, the facility needs an air-balance model—not only an exhaust schedule.

The model accounts for process exhaust, washroom and general exhaust, combustion air, relief paths, existing supply air, air transferred between zones, door leakage and desired pressure relationships. It should also consider which systems operate together. A plant can be stable on a normal shift and become severely negative when a batch process and loading-area exhaust start at the same time.

Make-up air is more than a matching airflow number

Replacement air must arrive in the right place, at an appropriate temperature and velocity, under a sequence that follows the exhaust system. In Ontario winters, unconditioned replacement air can create freezing risk, worker discomfort and process problems. Poor diffuser placement can send clean air directly into a hood, push contaminants across the operator or short-circuit to the exhaust.

The final air balance may intentionally keep a process zone slightly negative to adjacent clean spaces while maintaining the overall building at a manageable pressure. The correct relationship is project-specific and must not compromise capture, combustion safety, egress doors or the performance of other building systems.

What the Design Basis Must Establish

A defensible design starts with process information and field verification. Where hazardous biological or chemical agents may be involved, ventilation engineering should be coordinated with the employer's exposure-control strategy and qualified industrial hygiene input. Safety data sheets are useful, but they are not a substitute for understanding the actual process, concentration, temperature and operating conditions.

Airflow calculations may address hood capture or containment, duct transport velocity where applicable, branch balancing, pressure losses, fan duty, discharge, make-up air, room heat balance and building pressure. The analysis should be transparent enough that selections and construction documents can be checked against it.

Heating, Controls, Electrical, Roof and Structure

Heating and energy

Large exhaust systems can create a major winter heating load. The design should evaluate make-up air temperature, discharge location, freeze protection, burner or hydronic capacity, gas availability and operating schedule. Heat recovery may be attractive, but process contamination, fouling, corrosion, fire risk and maintenance can limit which technologies are appropriate. A project-specific heating and cooling load analysis helps establish the real impact on the building.

Controls and proof of operation

Sequence exhaust and replacement air so required systems start, prove and fail safely. Typical interfaces can include fan status, airflow or pressure proving, burner safeties, freeze protection, filter alarms, VFD control, process interlocks and building automation monitoring. A system that is balanced once but not controlled through real operating modes will not remain balanced.

Electrical, roof and structural interfaces

Fans, make-up air units, electric heat, controls and treatment equipment add electrical load and may require new feeders, disconnects and available-capacity verification. Roof-mounted equipment also brings curb, opening, weight, support, drainage, access and weatherproofing requirements. ETEM's HVAC electrical coordination guide explains the electrical handoffs in more detail, while our factory electrical capacity guide addresses broader plant expansions.

Ontario Permits, Worker Exposure and PSR Context

Ontario Regulation 851 for Industrial Establishments requires adequate ventilation so the workplace atmosphere does not endanger workers, and it contains specific replacement-air and exhaust-discharge requirements. Where worker exposure to biological or chemical agents is involved, Ontario Regulation 833 establishes exposure-control obligations, including the use of engineering controls where reasonably necessary.

A pre-start health and safety review (PSR) may be required when the prescribed circumstances in Regulation 851 apply. Item 8 can be relevant where a new or modified process uses or produces a hazardous biological or chemical agent and a ventilation system is used to control exposure to the limits under Regulation 833. This is not a blanket rule for every exhaust fan; the process, modification and prescribed circumstances must be evaluated.

Building-permit requirements depend on the jurisdiction and scope. The City of Toronto's current stand-alone mechanical guide, for example, identifies make-up air and exhaust as add-on systems and includes special ventilation systems such as spray booths and dust collectors. Submissions can require system layouts, equipment information, load calculations, duct calculations and ventilation calculations. See our broader guide to mechanical permit drawings in Ontario.

Processes involving combustible dust, flammable vapours, corrosive materials or other special hazards require hazard-specific analysis. General comfort-HVAC rules do not replace applicable fire, explosion, occupational hygiene or environmental requirements. ASHRAE Standard 62.1 can apply to occupied non-process spaces within industrial buildings, but it is not by itself an industrial process-ventilation design manual.

Drawings, Calculations and Deliverables

The appropriate deliverables depend on the process, project stage and approval path. A coordinated industrial ventilation package commonly includes:

• Existing-condition survey, process description and design-basis narrative.
• Exhaust, make-up air and pressure-balance calculations for relevant operating modes.
• Hood or source-capture details, airflows and installation criteria.
• Duct layouts, sizes, materials, pressure class, access and balancing provisions.
• Fan, make-up air and treatment-equipment schedules with project-specific duty points.
• Discharge, outdoor-air intake and roof-penetration coordination.
• Heating, gas or hydronic requirements and winter operating strategy.
• Control sequence, interlocks, safeties, alarms and BAS points.
• Electrical load, feeder, disconnect and controls-power coordination.
• Structural, fire-protection, environmental or industrial hygiene coordination notes where applicable.
• Permit, tender and construction documents appropriate to the agreed scope.
• Field review, testing, balancing and commissioning requirements.

A permit submission and a construction package do not always answer the same questions. If the owner wants comparable bids and fewer field assumptions, the documents should define materials, controls, interfaces, testing and acceptable substitutions—not only the minimum information required for review.

Selecting an Industrial Ventilation Consultant

The strongest consultant is not simply the one who can draw a duct route. Look for a team that asks about the process, materials, operating modes, people and existing performance before selecting equipment. The scope should explain who establishes the hazard and exposure basis, who performs measurements, who designs the ventilation system, and how mechanical, electrical, structural, fire and controls work will be coordinated.

For an initial conversation, send enough information to understand the process and the problem. ETEM can then identify whether the first step should be a site investigation, measurement program, feasibility study, permit design or coordinated construction package.

A Practical Industrial Ventilation Workflow

1. Define the business and process objective. Document the production change, complaint, compliance driver, operating schedule, outage limits and target construction window.
2. Survey the existing facility. Confirm process locations, fans, hoods, ducts, make-up air, controls, utilities, roof conditions and available records.
3. Establish the hazard and design basis. Coordinate material information, exposure or industrial hygiene input, applicable codes, PSR assessment and permit strategy.
4. Measure representative operation. Where needed, record airflow, pressure, temperature and system behaviour with the relevant processes and doors operating.
5. Develop the system air balance. Size capture, exhaust, ductwork, fans, replacement air, heating and pressure relationships together.
6. Coordinate every interface. Align mechanical, electrical, controls, roof, structure, fire protection, process equipment and construction sequencing.
7. Issue and review project documents. Support permit, procurement, tender and construction with coordinated criteria and submittal review.
8. Test the installed performance. Balance, commission and verify capture, pressure, controls and safety functions under agreed operating conditions.

What to send ETEM for an initial review

Useful starting information includes the facility address, process description, materials and safety data, photos or layouts, fan and equipment nameplates, operating schedule, known heat, odour, dust or pressure issues, existing airflow or industrial hygiene reports, roof and utility information, planned production changes and the desired project schedule.

Technical and Regulatory References

1. Ontario Regulation 851 — Industrial EstablishmentsOfficial regulation containing ventilation, replacement-air and exhaust-discharge requirements for industrial establishments.
2. Ontario Regulation 833 — Control of Exposure to Biological or Chemical AgentsOfficial regulation addressing occupational exposure limits, engineering controls and exposure assessment requirements.
3. Ontario — PSR Guideline, Item 8Provincial guidance on prescribed circumstances involving hazardous biological or chemical agents and ventilation systems used to control exposure.
4. City of Toronto — Stand-alone Mechanical (HVAC)Municipal submission guidance covering make-up air, exhaust, special ventilation and supporting mechanical documentation.
5. Government of Ontario — Ontario's Building CodeOfficial access point for the current Ontario Building Code and compendium information.
6. ASHRAE — Standards 62.1 and 62.2Official overview of ventilation and indoor-air-quality standards; industrial process applications require an appropriate process-specific design basis.
7. NFPA 91 — Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Particulate SolidsOfficial publication access for a hazard-specific exhaust-system standard; applicability must be evaluated for the process and jurisdiction.

Frequently Asked Questions