| I. Application & Placement |
| Draft Type |
Primarily Induced Draft Top/Discharge |
Primarily Forced Draft Bottom/Inlet |
| Airflow Direction |
Parallel to the fan axis straight through |
Perpendicular to the fan axis air enters center, exits tangentially |
| Typical Use |
Large industrial, commercial, and HVAC towers |
Smaller, packaged, or indoor units; ducts and tight spaces |
| II. Performance Characteristics |
| Air Volume Capacity |
Very High High flow rate |
Moderate to High |
| Static Pressure Handling |
Low Best for low system resistance |
High Can overcome high internal and external static pressure losses |
| Energy Efficiency |
Generally Higher Especially with large-diameter, low-speed fans |
Lower than Axial for large, free-standing towers more complex air path |
| Noise Profile |
Lower sound pressure at low speeds; noise radiates upward |
Can be Noisy; noise is generally concentrated at the air inlet near the ground |
| III. Design & Mechanical |
| Blade Material |
FRP, Aluminum Alloy, Stainless Steel |
Galvanized Steel or Aluminum Housing and Impeller |
| Airflow Control |
Excellent Pitch adjustment allows precise flow and energy optimization |
Good Controlled by VFDs - Variable Frequency Drives |
| Operating Speed |
Low to Medium ∼150 to 600 RPM for large fans |
High ∼900 to 1,800 RPM |
| Motor Placement |
Usually Outside the wet air stream Induced Draft setup |
Motor is often Inside the dry air stream |
| IV. Long-Term Maintenance |
| Maintenance Access |
Easy access to gearbox/motor through the fan stack |
Access can be restricted in tight enclosures |
| Motor Life |
Longer life due to location outside the saturated exhaust |
Generally good, as motor is in the drier inlet air |