Boiler Induced Draft System

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.

Draft System Difference

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.

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.

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.

System Process

A practical selection starts by understanding the complete flue-gas route rather than treating the induced draft fan as an isolated machine.

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.

Before Final Fan Selection

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.

Operating Diagnosis

Operating symptoms often indicate a mismatch between fan duty, system resistance, temperature condition or dust-control arrangement.

Selection Input

Complete working-condition data enables faster and more reliable comparison with the available boiler-fan range.

Product Direction

Select a model below to open its individual product page. Final fan selection must still use the actual operating point and working conditions.

For existing boiler fan replacement projects, QIYUE FAN can review original fan nameplates, GA drawings and operating conditions for model matching.

Project Type

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

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

Project Configuration

Configuration availability depends on the selected fan series, machine size, working conditions and factory confirmation.

✓ C-Type or D-Type Drive

✓ Left or Right Rotation

✓ Outlet Angle Matching

✓ Motor and Power Standard

✓ Temperature-Oriented Structure

✓ Dust and Wear Review

Primary Product Family

Boiler Induced Draft Fans

Combustion-Air Product Family

Boiler Forced Draft Fans

Thermal-Duty Product Family

High-Temperature Industrial Fans

Technical Questions

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.

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.

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.

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

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.

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.