Boiler Draft & Flue-Gas Exhaust
Boiler Induced Draft System
A boiler induced draft system removes flue gas, maintains suitable furnace negative pressure and overcomes resistance from ducts, dampers, dust collectors and the chimney. QIYUE FAN supports preliminary boiler ID fan matching according to the actual boiler duty, flue-gas condition and exhaust-system parameters.
Selection focus: operating airflow, total system resistance, normal and maximum flue-gas temperature, dust condition, drive arrangement, rotation and outlet direction.
Typical Flue-Gas Route
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BOILER
Combustion & hot flue gas
FLUE DUCT
Friction and local losses
DUST CONTROL
Collector resistance
ID FAN
Creates draft pressure
CHIMNEY
Final discharge
Orange-red elements indicate the high-temperature flue-gas direction.
System Duty
Flue-Gas Extraction
Control Target
Stable Negative Pressure
Selection Basis
Airflow + Total Resistance
Application Overview
What the Induced Draft System Must Achieve

The induced draft fan is installed on the exhaust side of the boiler system. It pulls combustion products through the downstream flue-gas path and helps keep the furnace operating under a controlled negative-pressure condition.

The fan cannot be selected only by boiler capacity, fan size or motor power. Actual performance depends on the required operating airflow and the total resistance created by the complete system.

For a new boiler project or replacement fan, QIYUE FAN reviews the boiler duty, fuel, gas temperature, dust-control equipment, duct arrangement, existing operating point and installation limitations before suggesting a suitable model direction.

01
Extract Boiler Flue Gas
Move combustion gas through the duct, treatment equipment and discharge path.
02
Maintain Furnace Draft
Support stable negative pressure without excessive suction that disturbs combustion.
03
Overcome System Resistance
Provide sufficient pressure after duct, elbow, damper and collector losses are included.
04
Match Real Site Conditions
Confirm temperature, dust, rotation, outlet angle, drive type, motor and installation space.
Draft System Difference
Forced Draft Fan and Induced Draft Fan Work Together
In many boiler systems, the forced draft fan supplies combustion air while the induced draft fan pulls flue gas through the boiler, dust-control equipment and chimney.
FD Fan
Forced Draft Fan Supplies Combustion Air

The forced draft fan pushes fresh air into the boiler furnace or combustion system. Its duty is related to air supply, combustion stability, air volume control and burner-side resistance.

● Located on the air-supply side
● Handles clean air or preheated air
● Selected by combustion air volume and air-side resistance
ID Fan
Induced Draft Fan Extracts Flue Gas

The induced draft fan pulls hot flue gas through the boiler exhaust route and helps maintain furnace negative pressure. It must consider temperature, dust, duct resistance and dust-control equipment.

● Located on the exhaust side
● Handles flue gas, heat and possible dust
● Selected by flue-gas volume and total exhaust-system resistance
System Process
How a Boiler Induced Draft System Works
A practical selection starts by understanding the complete flue-gas route rather than treating the induced draft fan as an isolated machine.
1
Boiler Combustion
Fuel combustion produces hot flue gas and determines the initial gas volume handled by the exhaust system.
2
Heat-Transfer & Duct Section
Gas passes through boiler heating surfaces and ductwork, creating friction and local pressure loss.
3
Dust or Gas Treatment
Cyclone, bag filter, scrubber or other equipment may create a major part of total system resistance.
4
Induced Draft Fan
The ID fan supplies the pressure required to pull the design gas volume through the exhaust route.
5
Chimney Discharge
Flue gas is discharged while the system maintains the required furnace draft condition.
Pressure Selection
Why Total System Resistance Determines Fan Pressure

The boiler ID fan must deliver the target airflow after all downstream resistance has been included. A free-air airflow value or motor-power comparison cannot represent the real operating point.

Dust accumulation, damper position and filter condition may change resistance during operation. A practical design therefore needs a confirmed design point and a reasonable operating margin.

Required fan pressure = duct friction + elbows and transitions + dust collector + damper + chimney and outlet losses + project allowance
Dust CollectorMajor loss
 
Duct FrictionLength-based
 
Elbows & TransitionsLocal loss
 
DamperVariable
 
Chimney / OutletFinal section
 
The bars illustrate relative resistance sources only and are not project calculation values.
Before Final Fan Selection
Where Boiler ID Fan Pressure Loss Comes From
For boiler induced draft fan selection, pressure loss should be reviewed across the complete flue-gas route. A dust collector, scrubber or long duct route can change the final fan model even when the boiler capacity is the same.
01
Boiler Pass Resistance
Heating surfaces, furnace structure and boiler gas passages create the base resistance that the induced draft fan must overcome.
02
Economizer / Air Preheater
Heat-recovery equipment may add pressure loss, especially when ash deposition or narrow passages increase resistance during operation.
03
Dust Collector Resistance
Bag filters, cyclones and other dust-removal equipment are often the largest resistance item in boiler ID fan selection.
04
Scrubber Resistance
Wet treatment equipment, spray towers or scrubbers should be included when the system has gas cleaning before discharge.
05
Duct, Elbow and Damper Loss
Long ducts, bends, reducers, transitions and damper opening position should be included in total resistance calculation.
06
Chimney and Outlet Loss
Chimney height, outlet arrangement and final discharge condition influence system draft and should be reviewed before quotation.
Operating Diagnosis
Common Problems in Boiler Draft Systems
Operating symptoms often indicate a mismatch between fan duty, system resistance, temperature condition or dust-control arrangement.
01
Insufficient Draft
Poor flue-gas discharge, furnace positive pressure or unstable combustion may indicate insufficient fan pressure, increased resistance or duct blockage.
02
Excessive Negative Pressure
An oversized or poorly controlled fan may increase energy consumption and make combustion adjustment more difficult.
03
Dust and Impeller Wear
Dust concentration, particle characteristics, collector efficiency and fan position influence impeller and casing life.
04
High Flue-Gas Temperature
Temperature affects material, bearing arrangement, transmission, motor position and cooling requirements.
Selection Input
Parameters Required for Boiler ID Fan Selection
Complete working-condition data enables faster and more reliable comparison with the available boiler-fan range.
Boiler and Process Information
● Boiler capacity and boiler type
● Fuel type and combustion method
● New installation or replacement project
● Continuous operating hours and load variation
● Normal and maximum flue-gas temperature
● Dust or impurity condition in the gas
● Existing fan model or boiler supplier data
Fan and System Information
● Required airflow in m³/h or CFM
● Static pressure, total pressure or resistance calculation
● Dust collector type and rated pressure loss
● Duct length, diameter, elbows and transitions
● Chimney height and outlet arrangement
● Rotation direction and outlet angle
● Drive type, motor voltage, frequency and phase
Product Direction
Recommended QIYUE FAN Boiler Fan Model Directions
Select a model below to open its individual product page. Final fan selection must still use the actual operating point and working conditions.
Primary Boiler ID Fan Directions
Start with these series when the project is mainly about induced draft, flue-gas extraction and boiler exhaust resistance.
Y6-30
Y6-30 Boiler Induced Draft Fan
For small industrial boiler flue-gas extraction where airflow, pressure, rotation, outlet direction and drive arrangement require matching.
View Y6-30 Product Page →
Y5-47
Y5-47 Boiler Induced Draft Fan
For industrial boiler flue-gas exhaust and smoke or dust-removal systems after the required operating parameters are confirmed.
View Y5-47 Product Page →
Y5-48
Y5-48 Boiler Induced Draft Fan
For boiler smoke extraction and dust-removal systems where resistance, gas temperature and continuous-duty operation need review.
View Y5-48 Product Page →
Y8-39
Y9-38
Y8-39 / Y9-38 Boiler Induced Draft Fan
For boiler induced draft duties requiring higher pressure capability, subject to airflow, pressure, speed, motor power and flue-gas condition.
View Y8-39 / Y9-38 Product Page →
More Boiler Fan Options
These series can be reviewed for forced draft, induced draft, larger airflow or higher-resistance boiler systems after confirming the operating point.
G/Y4-73
G/Y4-73 Boiler Centrifugal Fan
For boiler forced-draft and induced-draft matching. The correct G or Y configuration depends on the required air-supply or flue-gas exhaust duty.
View G/Y4-73 Product Page →
GY5-51
GY5-51 Boiler Forced / Induced Draft Fan
For medium and larger steam-boiler systems where airflow, pressure, system scale and forced or induced draft duty need matching.
View GY5-51 Product Page →
GY6-41
GY6-41 Industrial Boiler Blower and ID Fan
For industrial boiler forced-draft or induced-draft applications after the boiler duty, resistance and gas condition are confirmed.
View GY6-41 Product Page →
GY6-51
GY6-51 Large-Capacity Boiler Draft Fan
For larger airflow and higher-resistance boiler draft systems where drive arrangement, motor power and installation conditions need confirmation.
View GY6-51 Product Page →
Selection note: Model names and boiler capacity provide only a preliminary direction. Final selection must be checked against airflow, total pressure, gas temperature, dust condition, system resistance, speed, motor and installation layout.
Project Type
New Boiler Projects and Replacement Fan Projects
New System
Design from Boiler and Duct Data

For a new project, provide the boiler duty and planned exhaust-system route. Airflow and pressure should be based on the complete resistance calculation.

● Boiler capacity, fuel and process duty
● Flue-gas volume and temperature
● Dust collector or treatment equipment
● Duct layout, chimney and power standard
Replacement
Match the Site and Correct the Problem

Original fan data and current operating problems help determine whether the new unit should match the existing duty or correct a selection mismatch.

● Fan and motor nameplate photos
● Current airflow, pressure, speed and power
● Inlet, outlet and foundation dimensions
● Rotation, outlet angle and operating issue
Project Configuration
Available Configuration Directions
Configuration availability depends on the selected fan series, machine size, working conditions and factory confirmation.
✓ C-Type or D-Type Drive
Selected according to fan series, speed, motor arrangement and maintenance access.
✓ Left or Right Rotation
Confirmed from the motor side and matched to the site duct arrangement.
✓ Outlet Angle Matching
Available angle options vary by model and should be confirmed before production.
✓ Motor and Power Standard
Voltage, frequency, phase and protection requirements can be reviewed.
✓ Temperature-Oriented Structure
Material, bearing, transmission and motor position depend on temperature.
✓ Dust and Wear Review
Impeller, casing and treatment direction can be discussed for confirmed dust conditions.
Non-standard features are available subject to working-condition review, model compatibility and factory confirmation. Please provide drawings or site dimensions when connection or foundation matching is required.
Continue from System Design to Product Selection
Related Boiler Fan Product Families

Use the induced-draft family as the primary product entry for this system page. The forced-draft and high-temperature families provide the corresponding combustion-air and thermal-duty directions.

Primary Product Family
Boiler Induced Draft Fans

Compare Y6-30, Y5-47, Y5-48, Y8-39 / Y9-38 and larger boiler ID fan directions by airflow, pressure, temperature and resistance.

View Boiler ID Fans →
Combustion-Air Product Family
Boiler Forced Draft Fans

Compare combustion-air supply, burner pressure, air-preheater resistance and clean-air-side boiler fan directions.

View Boiler FD Fans →
Thermal-Duty Product Family
High-Temperature Industrial Fans

Review furnace, kiln, boiler and thermal-process hot-gas fan directions when temperature changes material and structure.

View High-Temp Fans →
Technical Questions
FAQ About Boiler Induced Draft Systems
What Is the Function of an Induced Draft Fan in a Boiler System?

It pulls flue gas through the boiler exhaust route and helps maintain the required furnace negative pressure. It must provide the target airflow while overcoming the total resistance of the connected system.

How Do I Determine the Required Boiler ID Fan Pressure?

The required pressure should include duct friction, elbows, transitions, dampers, dust collector or treatment equipment, chimney and discharge losses. The fan must then be checked at the required airflow.

Where Is the Induced Draft Fan Installed?

It is normally installed on the downstream exhaust side, often after the main dust-removal equipment and before the chimney. Final location depends on the boiler process and system design.

Can an ID Fan Be Selected Only by Boiler Capacity?

Boiler capacity is useful for preliminary screening, but final selection also requires airflow, total pressure, temperature, dust condition, system resistance and installation arrangement.

What Information Is Needed to Replace an Existing Boiler Fan?

Send the original fan and motor nameplates, operating data, inlet and outlet sizes, rotation, outlet angle, foundation dimensions, site photos and the current operating problem.

Which QIYUE FAN Boiler Fan Model Is Suitable for My Boiler?

The suitable series depends on the operating point and project conditions. Send boiler capacity, airflow, pressure, temperature, dust collector, flue-gas condition, drive requirement and installation layout for preliminary matching.

Fan Selection Support
Send Your Boiler System Parameters
QIYUE FAN can review the boiler application, operating airflow, total pressure, flue-gas temperature, dust-control equipment, duct resistance, rotation, outlet angle and installation conditions before suggesting a suitable fan direction.
Send: Boiler Capacity | Fuel | Airflow | Total Pressure | Normal / Max Gas Temperature | Dust Collector | Duct Layout | Existing Fan Nameplate | Rotation / Outlet Angle | Power Supply | Quantity
Manager Zhao
Industrial Ventilation Fan Supplier
SHANDONG QIYUE FAN CO., LTD.
Tel / WeChat / WhatsApp: +86 15653305981
Factory: Dongchen Industrial Park, Zhoucun District, Zibo, Shandong, China
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