Centrifugal Downblast Roof Mounted Exhaust Fans

Downblast exhaust fans serve to safely evacuate contaminated air, chemical fumes, or heat from industrial facilities while directing the discharge downward to prevent re-entry into the building. Their purpose includes protecting air quality, meeting ventilation codes, and preventing corrosive gases from damaging roof-mounted HVAC equipment. In chemical processing plants, downblast fans constructed from corrosion-resistant materials like PVC and polypropylene handle aggressive exhaust streams up to 125,000 CFM while withstanding up to 24 inches of static pressure. The downward discharge pattern also reduces noise impact on surrounding areas.

Use upblast exhaust fans when vertical discharge is needed to achieve stack effect and disperse light contaminants high above the roofline. Choose downblast fans when handling heavy, corrosive, or odorous exhaust that must be directed away from rooftop equipment and air intakes. Downblast configurations are preferred in chemical processing, plating operations, and facilities with nearby air handling units or occupied spaces. IPF Colasit's CRDV downblast fans excel in corrosive environments where metal fan components would fail, offering PPs-EL spark-resistant options for explosive atmospheres and handling static pressures upblast fans cannot manage.

A centrifugal downblast fan uses a rotating impeller with forward or backward-curved blades to accelerate air radially outward, then redirects it downward through a discharge opening. This design generates higher static pressure capabilities than axial fans—up to 24 inches in IPF Colasit models—making them suitable for ducted systems with high resistance. The centrifugal mechanism paired with downblast orientation provides powerful exhaust capacity (up to 125,000 CFM) while directing corrosive or contaminated air away from the roof surface. Thermoformed PVC and polypropylene construction ensures longevity in harsh chemical environments.

Thermoformed PVC, polypropylene, and spark-resistant PPs-EL materials provide superior corrosion resistance for chemical exhaust applications. These thermoplastics eliminate metal corrosion concerns entirely, with no metal components in the airstream except stainless steel motor mounts. IPF Colasit's auto-welded construction creates seamless, leak-proof casings that withstand acids, caustics, and aggressive chemical vapors. Customers report 25+ year service lives in environments where metal fans fail within months. ISO 9001-2008 manufacturing standards ensure consistent material quality and welding integrity across all units.

Airflow requirements depend on room volume, air change rates mandated by codes, process heat loads, and contaminant generation rates. Chemical processing facilities typically require 10-30 air changes per hour depending on hazard classification. Calculate CFM by multiplying room volume (cubic feet) by required air changes per hour, then dividing by 60. IPF Colasit's centrifugal downblast fans handle 50,000-125,000 CFM with up to 24 inches static pressure, accommodating high-resistance ductwork and heavy contaminant loads. Consult with ventilation engineers to determine precise requirements based on your specific chemical processes and safety regulations.

IPF Colasit's belt drive centrifugal fans feature sealed bearings requiring no greasing for 100,000 operating hours—dramatically reducing maintenance compared to metal fans. Routine maintenance includes quarterly belt tension inspection, annual motor bearing lubrication per manufacturer specifications, and semi-annual impeller cleaning to remove chemical deposits. The corrosion-resistant PVC and polypropylene construction eliminates rust, scaling, and material degradation common in metal fans. Direct drive models require even less maintenance with no belts to adjust. The thermoformed, auto-welded construction creates seamless surfaces that resist buildup and simplify cleaning during scheduled shutdowns.