Roof fans are specified by their mounting system and discharge direction, not by airflow volume alone. Two fans with identical airflow ratings can perform very differently on the same building if one is mounted on a profile base that suits the roof sheeting and the other requires a fabricated upstand. The correct variant depends on the roof profile, the type of contaminant being extracted, whether the application needs supply or exhaust, and how much installation time the project allows.
Fanquip manufactures four roof fan variants: vertical discharge, profile base hooded, curb base hooded, and filtered roof supply. Each suits different building types and applications. This guide covers what distinguishes them and how to match the right fan to your facility.
If you are still confirming that a roof-mounted fan is the right approach, the industrial fan types explained guide covers the full range. Otherwise, browse the roof fan range and read on.
Why roof fan selection starts with the roof profile
Every roof fan mounts through a penetration in the roof, and the mounting method has to suit the roof material and profile. This is the first selection filter, and it comes before airflow volume, before fan type, and before any performance specification.
Profile base fans suit standard corrugated and trapezoidal roof sheeting. The fibreglass profile base overlaps and underlaps the existing sheets from all sides, creating a weatherproof seal without upstands or flashings. Curb base fans suit any roof profile, including non-standard and custom sheeting, by mounting on a fabricated timber or steel curb upstand. Vertical discharge fans also mount on curb upstands, with the discharge directed vertically rather than out through a hood. Filtered supply fans mount on curbs where clean supply air is the requirement rather than exhaust.
Assess the roof profile before shortlisting products. A facility with standard corrugated sheeting has a faster and cheaper installation path available to it than one with a custom profile, and knowing which category your roof falls into narrows the selection immediately.
The four Fanquip roof fan variants
Three of the four variants exhaust air out of the building, and one supplies filtered air into it. Within the three exhaust variants, the distinction is the mounting method and whether the discharge is directed vertically into the atmosphere or out at roof level through a hood.
Vertical discharge roof fan
The vertical discharge roof fan directs exhaust air high into the atmosphere rather than discharging it at roof level. It also controls humidity by removing hot air as it rises to the ceiling, which prevents moisture accumulating in the roof space.
When to choose it. Specify vertical discharge where the exhaust must be directed away from the building envelope. This applies to dust, steam, smoke, and noxious gases, and to any contaminant where roof-level discharge would cause re-entrainment back into the building, generate odour complaints from neighbouring properties, or contaminate adjacent HVAC intakes. Where a discharge height requirement forms part of an environmental approval, vertical discharge is generally the only compliant roof-mounted option.
Construction. Hot dip galvanised, extra heavy-duty, and Australian made. Weatherproof butterfly dampers close when the fan is not running, preventing rain and wind ingress through the penetration.
Sizes. 300mm to 1500mm, with custom sizing available.
Industries. Manufacturing facilities extracting fumes from processes that generate hazardous gases. Food processing plants discharging odour and steam away from adjacent areas and neighbouring sites. Mining and metals operations directing fume and gas discharge clear of the building. Laundry services managing steam-heavy exhaust. Hospitals, office buildings, and warehouses also use vertical discharge units where discharge height matters.
Profile base hooded roof fan
The profile base hooded roof fan mounts directly onto the roof sheets using a fibreglass base shaped to match the roof profile. No upstands and no flashings are required, which reduces installation costs and time significantly compared with a curb-mounted alternative.
When to choose it. Specify profile base where the roof profile matches one of the six standard Fanquip profiles and installation speed and cost are priorities. On a project installing multiple roof fans across a large roof area, the installation saves compounds significantly.
Limitation. The profile base only suits the six standard profiles. If the roof profile does not match any of them, the curb base hooded fan is the correct choice.
Construction. Fibreglass and hot dip galvanised steel. The fibreglass profile base provides the weatherproof seal by overlapping and underlapping the existing roof sheets from all sides. A step-by-step installation guide is available for each profile. Like the curb base fan, the profile base is available in exhaust or supply air versions.
Industries. Warehouses, manufacturing facilities, and agricultural buildings where the roof profile is standard corrugated sheeting and fast installation matters. Agricultural sheds in particular are commonly built with standard profiles, making them well suited to profile base mounting.
Curb base hooded roof fan
The curb base hooded roof fan mounts on a fabricated upstand, with a heavy-duty hood preventing rain ingress through the discharge opening.
When to choose it. Specify curb base where the roof profile does not match any of the six standard profile base options, or where the mounting requires a fabricated upstand for structural or weatherproofing reasons. Curb base is also the correct choice where the fan needs to sit at a specific distance from major openings so that air travels across a large floor area before being extracted, creating cross-ventilation through the space rather than short-circuiting straight to the nearest extraction point.
For warehouse temperature management specifically, see using roof fans to maintain proper temperature in warehouses.
Dual function. The curb base fan can be configured for exhaust or supply air. It is one of three Fanquip roof fan variants offering a supply-air version, alongside the profile base hooded fan and the filtered roof supply fan.
Construction. Fibreglass or hot dip galvanised steel, with a heavy-duty hood. Available in a range of standard profile bases for installation flexibility where a partial profile match exists.
Sizes. 300mm to 1200mm.
Industries. Food processing plants, including washdown environments where exhaust is needed at ceiling level. Warehouses and cold stores. Laundry services managing steam-heavy exhaust. Any facility with non-standard or custom roof profiles.
Filtered roof supply fan
The filtered roof supply fan works in the opposite direction to the other three variants. Rather than exhausting air out of the building, it supplies clean, filtered air into the facility through the roof.
What it does. Delivering filtered air into the space creates positive pressure, which prevents unfiltered air from entering through gaps, doorways, dock openings, and other uncontrolled points. Instead of contaminated air leaking in, filtered air leaks out. This is the mechanism behind contamination control in sensitive production environments.
When to choose it. Specify a filtered roof supply fan where clean filtered supply air is required at ceiling level, where positive pressure must be maintained across a production area to prevent contaminant ingress, or where the facility has limited ceiling space for conventional supply ducting. The roof-mounted configuration suits buildings where there is no room for a ducted supply run below the ceiling line.
Key distinction. This is a supply fan, not an exhaust fan. The vertical discharge, profile base, and curb base variants remove air from the building. The filtered roof supply fan brings filtered air in. Facilities frequently need both, with supply fans maintaining pressure and air quality while exhaust fans remove heat and process contaminants.
Industries. Food processing facilities prevent airborne contamination from entering production areas. Pharmaceutical manufacturing maintains positive pressure across production zones. Electronics manufacturing prevents dust from reaching sensitive components.
For detailed guidance on this product in a food production context, including compliance considerations, see filtered roof supply fans in food processing environments.
Selecting the right roof fan: a practical decision framework
Four questions resolve most roof fan specifications.
Does your roof profile match a standard profile?
If yes, the profile base hooded fan removes the need for upstands and flashings and cuts installation time and cost. If not, the curb base hooded fan mounted on a fabricated upstand is the correct choice. This single question eliminates one of the two hooded variants immediately.
Does the exhaust need to discharge high into the atmosphere?
Where contaminants, odours, or fumes must be directed away from the building envelope, the vertical discharge fan is the correct choice. This applies where re-entrainment into adjacent air intakes is a risk, where a discharge height forms part of an environmental approval, or where odour management at neighbouring properties is a consideration. Profile base and curb base hooded fans discharge at or near roof level, which is acceptable for heat and general stale air but not for hazardous or odorous exhaust.
Do you need to supply air rather than exhaust?
The filtered roof supply fan is the only roof-mounted option delivering clean filtered supply air into the facility. Both the curb base and profile base hooded fans can also be configured to supply air, though unfiltered. Where filtered positive pressure supply is the requirement, specify the filtered roof supply fan.
What are your installation constraints?
Profile base offers the fastest and lowest-cost installation with no upstands or flashings. Curb base and vertical discharge both require a fabricated upstand, which adds installation cost and time. Weigh this against the operational requirements of the application. An installation saving does not justify specifying a hooded fan where the application genuinely requires vertical discharge.
Performance specification after the variant is chosen
Once the variant is settled, the performance specification follows. Selecting a fan on airflow alone leads to poor system performance, so both airflow and pressure need to be considered together.
Airflow and air changes. Airflow volume is measured in L/s or m³/h. As a starting guide, warehouses generally require 2 to 4 air changes per hour for general ventilation, while heavy manufacturing and high-heat plants require 10 to 15 ACH. Calculate the building volume, apply the appropriate ACH for the application, and size the fan or fans accordingly. Oversized fans cycle inefficiently and consume more energy than the application requires.
Static pressure. Static pressure is measured in Pascals. Open-air roof exhausts encounter minimal static pressure, which is one of the practical advantages of roof-mounted extraction over ducted alternatives. Where a roof fan connects to ductwork, however, the system resistance rises and the fan must be selected to deliver the required airflow at that actual operating pressure rather than at free air.
Drive type. Roof fans are available in direct drive and belt drive configurations. Direct drive units have fewer moving parts and lower maintenance requirements. Belt drive units allow speed adjustment through pulley ratio changes and keep the motor out of the airstream, which matters for hot or corrosive exhaust.
For a full comparison of the two, see belt drive vs direct drive axial flow fans.
Environmental conditions and materials. The temperature, humidity, and chemical makeup of the air being moved determine the construction and material selection. Corrosive fumes and high heat require specialised construction, with stainless steel casings available across the range. Hazardous atmospheres require appropriately rated motors to prevent ignition, and the hazardous area classification of the installation point needs to be confirmed before specification.
Maintenance. Schedule inspection and servicing every 6 to 12 months depending on the duty and environment, with routine cleaning of fan components to maintain airflow performance. Facilities running roof fans continuously in dusty or greasy environments should inspect more frequently.
Roof fans and wall fans: matching the mounting to the contaminant source
Wall fans extract at floor or process level, where contaminants are generated at bench height, at a machine, or at a workstation. Roof fans capture heat, steam, and fumes that rise naturally to ceiling level. The correct choice depends on where the contamination originates and where it travels.
Many facilities need both. Wall fans handle floor-level extraction close to the source, while roof fans manage the heat and fume load that accumulates above the occupied zone. Neither mounting is inherently superior.
For guidance on the wall-mounted side of the decision, see wall-mounted exhaust fan options for industrial facilities.
Frequently Asked Questions
What is the difference between a profile base hooded roof fan and a curb base hooded roof fan?
A profile base fan mounts directly onto the roof sheets using a fibreglass base that matches the roof profile, with no upstands or flashings required, cutting installation time and cost. A curb base fan mounts on a fabricated upstand and suits any roof profile, including those that do not match the six standard profile bases. If your roof profile matches a standard shape, the profile base is faster and cheaper to install. If not, curb base is the correct choice.
Can a roof fan supply fresh air as well as extract?
The curb base and profile base hooded roof fans can both be configured for exhaust or supply air. The filtered roof supply fan is specifically designed to supply clean, filtered air through the roof into a facility. The vertical discharge fan is exhaust-only.
What size industrial roof fan do I need?
Roof fan sizing depends on the floor area, ceiling height, required air changes per hour, and the type of contamination being extracted. As a guide, warehouses typically require 2 to 4 ACH while heavy manufacturing requires 10 to 15 ACH. Fanquip’s team can recommend the correct fan size and quantity for your facility’s specific requirements.
Which roof fan is best for food processing facilities?
Both the filtered roof supply fan for clean air supply and the curb base or profile base hooded fan for exhaust are used in food processing. The filtered roof supply fan is particularly relevant where positive pressure must be maintained to prevent airborne contamination.
A detailed guide to filtered roof supply fans in food processing environments covers the food industry application in full.
What are Fanquip roof fans made from?
Fanquip roof fans are manufactured in Australia from hot dip galvanised steel and fibreglass depending on the variant. All variants are available with stainless steel construction and IP56 or IP66 motor ratings for demanding environments.
Specify your roof fan with confidence
The roof profile determines the mounting. The contaminant determines the discharge direction. The application determines whether you need supply or exhaust. Work through those three in order and the correct variant becomes clear.
Browse the roof fan range to compare all four variants, or contact Fanquip with your roof profile, building volume, contaminant type, and required airflow in L/s or m³/h. Our team will confirm the correct variant, size, and construction for your facility.