Induced draft is a ventilation method where a fan or blower creates negative pressure to pull combustion gases and air through a furnace or boiler. This mechanical approach contrasts with natural draft systems, which rely on temperature differences and buoyancy. Induced draft fans are essential components in mid-efficiency and high-efficiency heating systems.
System Components and Function
The induced draft fan, typically located near the heat exchanger exit, pulls air into the combustion chamber and exhaust gases up through the flue. This fan operates at speeds ranging from 800 to 3,600 RPM depending on furnace size and design. Variable-speed motors adjust fan speed to match heating demand, optimizing airflow and reducing energy consumption.
Advantages in Heating Systems
Induced draft improves combustion efficiency by ensuring consistent airflow regardless of external conditions like wind or chimney blockages. Systems using induced draft achieve AFUE ratings of 85 to 95 percent. This technology allows furnaces to be installed in tight spaces and sealed combustion designs, making it standard in modern condensing furnaces serving residential and light commercial properties.