The main difference between a centrifugal ID fan and an axial flow fan is how they move air or gas against system resistance. A centrifugal fan changes airflow direction and builds higher static pressure, making it more suitable for boilers, furnaces, scrubbers, bag filters, dust collectors, dryers, and ducted exhaust systems. An axial fan moves air in a straight path and is better for high-volume, low-pressure ventilation or fume extraction.
When I review an ID fan requirement, I do not start with fan type. I first check airflow, static pressure, gas temperature, dust load, duct layout, gas composition, material of construction, impeller type, and duty cycle. The wrong choice may still “run,” but it can create low suction, high vibration, excess power consumption, bearing problems, and poor draft control.
For a basic understanding of induced draft duty, see this guide on how ID fans work before finalizing the comparison.
What is an ID fan?
An ID fan, or induced draft fan, is used to pull flue gas, hot air, fumes, vapour, or process exhaust through a system and maintain negative draft. It is different from an FD fan, which pushes fresh air or combustion air into the system.
In real plants, ID fans are commonly seen after equipment such as:
- Boilers
- Furnaces
- Kilns
- Dryers
- Scrubbers
- Bag filters
- Cyclones
- Dust collectors
- Chimneys
- Pollution-control systems
This matters because an ID fan usually works on the exhaust side, where the gas may be hot, dusty, corrosive, humid, or loaded with fine particles. That is why the fan type cannot be selected only by CFM.
For a more detailed difference between draft duties, read FD fan vs ID fan selection.
Centrifugal ID fan: how it works
A centrifugal fan pulls gas into the impeller near the center and throws it outward through the casing. The airflow usually changes direction by around 90 degrees before discharge. This design helps the fan develop higher static pressure compared with many axial fan arrangements.
In industrial ID fan duty, centrifugal fans are preferred when the system has resistance from:
- Long ducting
- Multiple bends
- Dampers
- Scrubbers
- Bag filters
- Cyclones
- Heat exchangers
- Chimney height
- Dust buildup
- High-temperature exhaust paths
A centrifugal ID fan is not selected simply because it is “stronger.” It is selected because the system needs pressure-building ability at the required duty point.
AS Engineers works with industrial centrifugal blower and fan configurations such as backward curved, backward inclined, radial blade, exhauster radial, high-temperature plug, and exhauster air handling designs. The right impeller depends on pressure, dust, temperature, abrasion, corrosion, and process duty, not only on the airflow number.
For deeper selection logic, see ID fan design, selection criteria, and operation.
Axial flow fan: how it works
An axial fan moves air parallel to the shaft, similar to a propeller-type flow path. Air enters and exits in the same general direction. This makes axial fans useful when a plant needs large airflow volume with low system resistance.
Axial fans are generally more suitable for:
- General industrial ventilation
- Fume extraction with low duct resistance
- Cooling air movement
- Workshop ventilation
- Large-space air movement
- Low-pressure exhaust applications
Axial fans can be custom-built for industrial requirements, but they are not always the right choice for ID fan duty. If the exhaust line includes filters, scrubbers, long ducting, dust loading, or high static pressure, an axial fan may fail to deliver the expected suction at the process point.
That is why the question should not be “Which fan gives more airflow?” The correct question is “Which fan can deliver the required airflow at the actual system resistance?”
Centrifugal vs axial ID fans: direct comparison
| Selection factor | Centrifugal ID fan | Axial flow fan |
|---|---|---|
| Airflow direction | Air changes direction through the impeller and casing | Air moves parallel to the shaft |
| Pressure capability | Better for medium to high static pressure | Better for low-pressure air movement |
| Best fit | Ducted exhaust, boilers, furnaces, scrubbers, bag filters, dust collectors | Ventilation, cooling, fume extraction, low-resistance exhaust |
| Dust handling | Better options are available for dusty and abrasive gas streams, depending on impeller design | More limited when dust load and system resistance are high |
| Temperature handling | Often preferred for hot gas and flue gas duties when designed correctly | Suitable only when temperature and duty conditions match design limits |
| Duct resistance | Handles bends, dampers, filters, scrubbers, and long ducts better | Performs best in simpler, lower-resistance paths |
| Maintenance risk | Dust buildup, imbalance, bearing load, alignment, and impeller wear must be managed | Blade wear, vibration, motor load, and installation alignment still matter |
| Common buyer mistake | Selecting only by motor HP or catalogue CFM | Selecting by free-air CFM and ignoring static pressure |
When should you choose a centrifugal ID fan?
Choose a centrifugal ID fan when the system has meaningful resistance and the fan must maintain stable draft. In most industrial exhaust applications, this is the safer starting point.
A centrifugal ID fan is usually the better choice for:
- Boiler flue gas exhaust
- Furnace exhaust
- Kiln exhaust
- Scrubber exhaust
- Bag filter exhaust
- Dust collector suction
- Dryer exhaust
- Hot air generator exhaust
- Chemical process exhaust
- Cement and mineral processing exhaust
- Power plant draft systems
For example, a bag filter ID fan is not just moving air. It is pulling dusty gas through filter bags, ducting, dampers, and discharge arrangements. If the fan cannot handle the pressure drop, suction reduces and dust collection performance suffers.
Similarly, a scrubber ID fan must pull gas through a pollution-control system where moisture, corrosion, pressure drop, and duct layout may affect fan reliability. This is where impeller design, MOC, balancing, and service access become important.
For boiler-specific context, see boiler ID fan functionality and importance.
When should you choose an axial flow fan?
Choose an axial flow fan when the application needs high air volume but does not require high static pressure. Axial fans are useful where air must be moved across a space or through a short, low-resistance path.
An axial fan may be suitable for:
- Factory ventilation
- General exhaust
- Fume extraction
- Cooling zones
- Air circulation
- Low-pressure duct ventilation
- Large-volume air movement
The mistake is using an axial fan as a shortcut for an industrial ID fan application with heavy resistance. A fan that performs well in open air may not perform well after connecting it to long ducting, a scrubber, a bag filter, or a hot exhaust line.
If the gas path includes heavy dust, high temperature, corrosive vapours, or high duct resistance, the fan selection should be reviewed carefully before choosing axial flow.
Why airflow alone can mislead buyers
Many purchase mistakes start from one line: “We need this much CFM.”
CFM is important, but it is only half the selection. A fan must deliver the required airflow at the required pressure. If a buyer compares two fan quotations only by airflow, the lower-cost option may fail at site because the actual duct resistance is higher than assumed.
Before selecting between centrifugal and axial flow fans, confirm:
- Required airflow volume
- Static pressure or total pressure requirement
- Gas temperature
- Dust load
- Gas composition
- Moisture and humidity
- Corrosion or abrasion risk
- Duct length and number of bends
- Equipment connected before and after the fan
- Chimney height or discharge condition
- Motor mounting arrangement
- Site altitude and ambient condition
- Operating hours per day
- Maintenance access
AS Engineers’ fan selection approach considers application, density, temperature, dust load, humidity, site location, altitude, material of construction, impeller blade design, and motor mounting arrangement. These factors decide whether the fan will run reliably after installation.
For a practical buyer-side guide, read ID fan selection and installation.
Centrifugal fan types used in ID fan applications
Not every centrifugal fan is the same. Within centrifugal ID fan selection, impeller design changes pressure capability, dust handling, efficiency, maintenance risk, and suitability for the process.
| Centrifugal fan type | Practical use case | Selection caution |
|---|---|---|
| Backward curved fan | Cleaner gas, efficient air movement, process ventilation, many industrial exhaust duties | Dust loading and temperature still need review |
| Backward inclined fan | High volume with controlled pressure and quieter operation in suitable applications | Not automatically suitable for abrasive dust |
| Radial blade fan | Dusty, particulate, and heavy-duty applications where ruggedness matters | Efficiency and noise must be reviewed against duty |
| Exhauster radial fan | Light dust and exhaust air applications | Dust type and loading should be checked |
| High-temperature plug fan | Furnace-ready and high-heat applications where design supports the temperature | Temperature limits require proper engineering review |
| Exhauster air handling fan | Abrasion-resistant construction for demanding exhaust handling | MOC and impeller wear risk should be reviewed |
If your application involves custom impeller needs, compare the duty with custom ID fan impeller requirements.
What happens when the wrong fan type is selected?
The wrong fan type may create problems slowly. The plant may initially accept the installation because the fan runs, but the process does not get stable suction.
Common symptoms include:
- Low draft at boiler, furnace, dryer, or dust collection point
- High motor load
- Excess vibration
- Bearing heating
- Unstable suction
- Dust leakage from process equipment
- Poor bag filter or scrubber performance
- Higher noise
- Frequent impeller cleaning
- Premature impeller wear
- Recurring alignment and balancing issues
In many cases, the problem is not only the fan. It may be the combination of wrong fan type, incorrect pressure estimate, changed ducting, worn impeller, damper position, dust buildup, or poor installation alignment.
For troubleshooting support, see common ID fan problems and how to fix them.
How to decide between centrifugal and axial fans
Use this practical decision path before sending an RFQ.
| Question | If answer is yes | Likely direction |
|---|---|---|
| Is the fan connected to a boiler, furnace, scrubber, bag filter, cyclone, dryer, or chimney? | The system has process resistance and draft control needs | Centrifugal ID fan |
| Is the main requirement general ventilation or air circulation? | Airflow volume matters more than static pressure | Axial fan |
| Is there heavy ducting with bends, dampers, filters, or pollution-control equipment? | Static pressure is a major selection factor | Centrifugal ID fan |
| Is the gas dusty, abrasive, hot, humid, or corrosive? | Impeller, MOC, and construction need careful review | Usually centrifugal, with duty-specific design |
| Is the path short and low-resistance? | Pressure requirement may be low | Axial fan may be suitable |
| Is the buyer comparing only CFM? | Selection is incomplete | Calculate pressure and duty point first |
| Is the existing fan failing after duct modification? | System resistance may have changed | Recheck fan curve and duty data |
For high-pressure or resistance-heavy air movement, this support guide on choosing a high-pressure blower may also help.
Industry examples: where each fan type fits
| Industry or system | Better starting point | Why |
|---|---|---|
| Boiler exhaust | Centrifugal ID fan | Needs negative draft and pressure handling through flue gas path |
| Furnace exhaust | Centrifugal ID fan | Temperature, ducting, and draft stability matter |
| Bag filter system | Centrifugal ID fan | Filter pressure drop and dust loading are key factors |
| Scrubber system | Centrifugal ID fan | Moisture, corrosion, and pressure drop must be reviewed |
| Cement plant dust exhaust | Centrifugal ID fan | Dust, abrasion, and duct resistance are common |
| Chemical plant exhaust | Centrifugal ID fan | Gas composition, corrosion, and safety review may be needed |
| Factory ventilation | Axial fan | High air volume with lower pressure requirement |
| General fume extraction | Axial or centrifugal, depending on duct resistance | Short low-resistance paths may use axial; ducted systems may need centrifugal |
| Cooling air movement | Axial fan | Large-volume air movement with low pressure is common |
For broader industrial fan context, you can also review AS Engineers’ centrifugal blower product range and axial fans manufacturer page.
RFQ checklist for centrifugal vs axial ID fan selection
A good RFQ should help the manufacturer understand the actual plant condition. Sending only airflow and motor HP is not enough.
Before requesting a quotation, share:
- Application name: boiler, furnace, scrubber, bag filter, dryer, ventilation, or other
- Required airflow
- Required static pressure or total pressure
- Gas temperature at fan inlet
- Dust load and particle nature
- Gas composition
- Moisture or humidity level
- Corrosion or abrasion risk
- Duct layout, bends, dampers, and connected equipment
- Fan inlet and outlet arrangement
- Required material of construction
- Motor HP, RPM, and power supply preference, if already defined
- Existing fan details, if replacing
- Site location and altitude
- Operating hours and duty cycle
- Maintenance access limitations
This information helps avoid oversizing, undersizing, wrong impeller selection, wrong MOC, and repeated site issues.
For maintenance planning after selection, refer to ID fan maintenance dos and don’ts.
Which is better: centrifugal or axial ID fan?
Neither is universally better. A centrifugal fan is better when the plant needs pressure, draft stability, dust handling, and duct resistance capability. An axial fan is better when the plant needs high-volume air movement against low resistance.
For most industrial ID fan duties connected to boilers, furnaces, scrubbers, bag filters, dust collectors, dryers, and chimneys, centrifugal designs are commonly the stronger fit. For general ventilation, fume extraction, and large-volume low-pressure movement, axial fans can be the practical choice.
The correct answer depends on the duty point, not on the fan name.
FAQs
What is the main difference between centrifugal and axial ID fans?
A centrifugal fan changes airflow direction and develops higher static pressure, while an axial fan moves air parallel to the shaft and is better for high-volume, low-pressure movement. For industrial ID fan duty, centrifugal fans are usually preferred when ducting, filters, scrubbers, dust, heat, or system resistance are involved.
Is an ID fan the same as an FD fan?
No. An ID fan pulls exhaust gas, flue gas, fumes, or process air out of a system and helps maintain negative draft. An FD fan pushes fresh air or combustion air into the system. Boilers, furnaces, kilns, dryers, and pollution-control systems may use both, but their duties are different.
Can an axial fan be used as an ID fan?
Yes, but only when the application is suitable for axial flow, usually high airflow with low static pressure. For ducted exhaust, bag filters, scrubbers, boilers, furnaces, dusty gas, or high-temperature duty, a centrifugal ID fan is often more appropriate. Final selection depends on actual duty data.
Why are centrifugal fans common in industrial ID fan applications?
Centrifugal fans are common because many industrial ID fan systems require pressure-building ability. Ducts, bends, dampers, filters, scrubbers, cyclones, chimney height, dust load, and hot gas create resistance. A centrifugal fan is better suited to overcome these conditions when properly selected.
What data is needed to select between centrifugal and axial fans?
The key inputs are airflow, static pressure, gas temperature, dust load, gas composition, humidity, duct layout, connected equipment, MOC requirement, impeller type, motor arrangement, site altitude, and operating duty cycle. Motor HP alone is not enough for correct fan selection.
Conclusion
For centrifugal vs axial ID fan selection, send your application details, airflow, static pressure, gas temperature, dust load, duct layout, gas composition, and operating duty to AS Engineers. A practical review of these inputs can help avoid wrong fan type selection, poor suction, high vibration, and avoidable maintenance issues.
Karan Dargode works with AS Engineers, contributing practical insights on industrial fans, ID fans, FD fans, high-pressure blowers, paddle dryers, sludge dryers, and process equipment used in demanding plant environments. His writing focuses on equipment selection, reliability, maintenance, application fitment, and clear technical guidance for industrial buyers and plant teams.