Free Sample
The Complete Handbook of Fans
The practical reference for professionals, businesses, and serious hobbyists who install, choose, maintain, or profit from fans
by Alumigogo Books
Chapter 1: Understanding Fans
A fan is a mechanical device that moves air. That simple sentence obscures a critical reality: fans are among the most commonly misunderstood and incorrectly applied climate control tools in homes and buildings. Most people have an intuitive understanding of fans—a desktop fan cools you down; a bathroom exhaust fan removes moisture; a whole-house fan circulates air through a home. But that intuitive understanding breaks down quickly when you need to choose a fan for an application, install one correctly, or understand why an installed fan isn't performing as expected. The gap between how fans actually work and how most people think about them is where expensive mistakes happen.
To understand fans properly, you need to grasp two foundational concepts: airflow and pressure. Airflow is measured in cubic feet per minute (CFM)—the volume of air a fan moves. Pressure is the resistance the fan must overcome to move that air. These two quantities are not independent. A fan has a fixed performance curve: at zero pressure (no resistance), it moves maximum air. As pressure increases, airflow decreases. Choose a fan based on airflow alone and ignore pressure, and you may buy a fan that moves very little air in your actual application.
Consider a concrete example. A bathroom exhaust fan manufacturer advertises a model as moving 110 CFM. The specification is technically true—in a test chamber with no ductwork, no bends, no filters, the fan moves 110 CFM. You buy it, install it in your