A smoke exhaust fan is a fire-rated ventilation fan certified to keep operating at high temperature, 280°C or 300°C, for 60 to 120 minutes during a fire, so it can extract heat and toxic smoke from escape routes while occupants evacuate. Its job is life safety, not comfort: by removing smoke from stairwells, lobbies, and shafts, it keeps visibility and tenable conditions for up to two hours and limits fire spread. Specifying the correct temperature rating and runtime is a code requirement, not an option.
Why Smoke Extract Fans Exist
During a fire, smoke spreads faster than flames and causes most casualties through toxicity and loss of visibility. A dedicated smoke extract system actively removes smoke from protected zones, while a pressurization system pushes clean air into stairwells to keep them smoke-free. Both depend on fans that survive the extreme environment. A normal supply or extract fan fails within minutes at 200°C to 300°C because its motor insulation, bearings, and impeller cannot tolerate the heat. Fire-rated fans are built from materials and components selected to perform throughout the certified period.
280°C vs 300°C Construction
| Rating | Continuous temperature | Typical certified runtime | Typical use |
|---|---|---|---|
| 280°C fan | 280°C | 60 to 120 minutes | Standard fire compartments, car parks, lobbies |
| 300°C fan | 300°C | 60 to 90 minutes | Higher-risk zones, long tunnels, plant rooms |
| 400°C fan (special) | 400°C | 60 to 120 minutes | Tunnels, high-hazard industrial fires |
The rating you need is dictated by the design fire temperature of the compartment and the local code. Once chosen, the fan, its motor, and the connected ductwork must all share the same certified duration.
Key Construction Features
Three features define a credible smoke exhaust fan. First, the motor is an F-class or H-class insulated, high-temperature type, often mounted outside the airstream (belt-driven or via a heat shield) so it stays below 80°C to 120°C even when the gas passing the impeller reaches 300°C. Second, the impeller and casing use steel rated for sustained high temperature, with a protective coating that does not off-gas toxic fumes. Third, bearings are selected for the duty and the whole assembly passes a type test at the declared temperature for the full duration, typically validated at 60, 90, or 120 minutes. Volume flow in fire mode commonly ranges from 5,000 to 120,000 m³/h and static pressure from 300 to 1,500 Pa depending on duct and shaft resistance.
When to Specify 280°C vs 300°C
- Specify a 280°C fan for most commercial buildings, car parks, and lobbies where code calls for 60 to 120 minutes at 280°C.
- Specify a 300°C fan for higher-risk compartments, longer evacuation tunnels, or where the design fire temperature exceeds 280°C.
- Specify a 400°C fan only for tunnel and high-hazard industrial applications with validated fire-engineering reports.
- Specify a dual-mode unit (smoke extract plus daily ventilation) when the system must also provide normal extract at 40°C to 60°C.
- Never substitute a standard ventilation fan for any certified smoke extract duty.
Certification and Compliance
A smoke exhaust fan must carry third-party fire-resistance certification referencing the relevant standard, such as EN 12101-3 for powered smoke and heat exhaust ventilators, alongside electrical and motor certifications. The certificate states the temperature, duration, and performance curve, and the installer must keep it on file for the authority having jurisdiction. Ductwork, dampers, and grilles in the smoke path need the same fire rating, and the system should be commissioned with a witness test that confirms the declared volume and pressure at the rated temperature. Regular annual inspection keeps the certification valid and the equipment ready.
Keruite manufactures this equipment at an 80,000 m² facility in Dezhou, China, with an in-house AMCA-210-style test laboratory; every unit is balanced to G2.5 and performance-tested before shipment.
System Design and Duct Routing
A smoke extract system is only as reliable as its ductwork. The extract ducts must be steel of the same fire rating as the fan, usually 280°C or 300°C for 60 to 120 minutes, and routed so they do not pass through unprotected zones that would heat the airstream beyond the fan limit. Keep bends to a minimum because each 90-degree elbow adds 30 to 80 Pa of loss, and size the main to hold velocity at 6 to 12 m/s so the fan still delivers 5,000 to 120,000 m³/h at the rated pressure of 300 to 1,500 Pa. Provide independent shafts for extract and pressurization so smoke cannot short-circuit into a protected stairwell, and fit fire dampers at every barrier penetration to preserve compartmentation.
Commissioning and Witness Testing
After installation the system is balanced and witness-tested: the fan is run at the rated temperature in a type-test or on-site heat simulation, and the delivered volume and pressure are confirmed within 10 percent of the certificate values. Differential pressure across each damper and shaft is logged, and the control sequence that starts extract and pressurization on a fire signal is verified end to end. Annual inspection then checks blade freedom, motor insulation above 1 megohm, and alarm links, because a seized damper or tripped breaker defeats the whole strategy. Documentation, including the EN 12101-3 certificate and the commissioning report, must stay with the building for the life of the system and be handed to the authority having jurisdiction.
Spare Parts and Lifecycle Cost
Over a 10 to 15 year service life the purchase price is a small part of cost; budget for motor replacement every 5 to 8 years, bearing sets, and the periodic witness re-test. Keeping the certified spare fan on site cuts downtime from days to hours during a fire-system fault, and a documented maintenance plan keeps the EN 12101-3 certificate valid for the authority having jurisdiction, and training the facility team to run the monthly function test keeps the life-safety system ready at all times.
FAQ
What is the difference between a 280C and a 300C smoke exhaust fan?
Both are fire-rated to keep running during a fire, but a 280°C fan is certified to operate at 280°C for 60 to 120 minutes, while a 300°C fan typically holds 300°C for 60 minutes. The choice follows local code and the fire compartment temperature expected; 300°C units suit higher-risk compartments and longer evacuation tunnels.
How long must a smoke exhaust fan run during a fire?
Most standards require continuous operation for 60 minutes, with many projects specifying 90 or 120 minutes at the rated temperature. The fan must maintain its declared volume and pressure throughout that period without bearing or motor failure, which is why dedicated high-temperature motors and thermal protection are mandatory.
Can a standard ventilation fan be used for smoke extraction?
No. Standard fans use insulation and bearings rated for ambient air up to about 60°C and will seize or ignite during a fire. Only fans carrying a fire-resistance certificate for 280°C or 300°C, with a declared F-class or H-class motor, may serve smoke extract duty in escape and fire-fighting shafts.
Where is a smoke exhaust fan installed in a building?
It is placed in smoke reservoirs, stairwell pressurization shafts, lift lobbies, or on the roof as part of a pressurization or extraction system. The fan should sit outside the fire compartment where possible, or be certified for the compartment temperature, and its ductwork must be fire-rated for the same duration as the fan.