Forced Draft (FD) Fans
AirPro // Applications
Industrial Forced Draft Fans
Forced draft fans, also referred to as pressure blowers or FD fans, focus the pressure and volume at the outlet of the fan to push air through a system, creating positive air pressure.
Applications calling for positive pressure include burners or combustion air, cooling, and air drying processes, fumes and gas elimination, tempered glass, and other conditioning processes. Accommodating higher process inlet temperatures, industrial applications use forced draft fans to push ambient air through burners to preheat air for boiler system efficiency.
Primary Industries for Forced Draft Fans
Forced draft fan applications are found across industries. However, because they are often used to feed combustion and high-temperature processes like dryers, burners, and boilers, you can be sure you’ll need forced draft fans in any or all of these industries:
- Agricultural Processing
- Automotive OEM
- Building Materials
- Chemical Processing
- Food Processing
- Glass Manufacturing
- Metals & Mining
- Oil & Gas
- Paint & Surface Coatings
- Pharmaceuticals
- Power Plants
- Printing, Packaging & Labeling
- Pulp & Paper
- Rubber & Plastics
- Semiconductor & Electronics
- Wastewater Treatment
Forced Draft Fan Selection & Specification
Forced draft fans handle high inlet temperatures by pushing ambient air through burners to preheat air and improve boiler system efficiency. Because they move cleaner ambient air, they typically experience less wear than induced draft fans, often requiring less structural support and offering longer mechanical life.
Typical Types of Forced Draft Fans
- Custom High-Pressure Blowers (HP#S)
- High-Pressure Radial Shrouded (HPSM / HPSL)
- Backward Curved (BCHS, BCLS, BCMS)
- Backward Inclined (BIHS)
- High-Pressure Radial Open (HPRM / HPRL)
Forced Draft (FD) Fan Arrangements
Fan arrangements indicate how the motors mount to and drive the fans. Forced draft fans typically call for direct-drive, Arrangement 4 fans with variable frequency drives. Larger systems may require direct-coupled configurations while some users prefer belt-drive for speed flexibility. These are the arrangement options:
Arrangement 1 – Belt Drive with an overhung impeller. The fan and motor mount separately to a unitary base.
Arrangement 4 – Direct Drive with an overhung impeller. A low-cost arrangement, the fan wheel mounts directly on the motor shaft.
Arrangement 8 – Direct Drive with an overhung impeller. The fan shaft is directly coupled to the motor shaft with a flexible coupling.
Forced Draft Fan Accessories & Design
Forced draft fans typically experience less wear than induced draft fans because they “push” clean, ambient air rather than pulling in hot, dirty airstreams. Their placement often makes upper bearings and fan blades more accessible for maintenance, while also shielding the fan and V-belt assembly from exposure to high-temperature air. These advantages reduce structural support requirements and can contribute to longer mechanical life.
However, even with ambient air, issues like system imbalance and excessive vibration can still arise. It’s essential to monitor fan vibration levels and promptly address any deviations from recommended thresholds to ensure reliable operation.
Accessory & Design Considerations
- Windbox Package – Creates a large, pressurized cavity to evenly distribute combustion air to one or more burners, ensuring balanced airflow through burner registers
- Flex Connectors – to accommodate shifting during rapid temperature change
- Spring Vibration Isolators – to protect the bearings and fan from excessive vibration and dangerous imbalances and help avoid outages that can be very costly
- Inlet Silencer – for noise control on the fan inlet
- Flow Control Options – includes inlet vane dampers, variable frequency drives (VFD), outlet dampers, or a combination, each offering control over airflow volume and pressure
- Inlet Filter or Screen – to keep debris from entering the airstream, preventing damage to the dampers
- Inlet Box – a solution for installations with limited ductwork space
- Purge Shaft Seal – helps prevent hot air from getting to the bearings through the shaft hole opening
- Vibration and Temperature Sensors – to monitor bearing and fan health in real time, enabling predictive maintenance and reducing unplanned downtime
- Split Housing – for easier maintenance access to the fan wheel and shaft for inspection and maintenance
- Proper Installation and Maintenance – to ensure safe startup and operations
Talk with Our Forced Draft Application Engineers
If you feel overwhelmed by all this information, don’t despair! We have a team of application engineers who are happy to talk with you and select the best fan for your application. You can call 715-365-3267, email fans@airprofan.com, or send us your information, and one of our engineers will connect with you.
