Forced Air

Forced air is the side of the building that moves conditioned air. An air handler pulls in return air, mixes in outdoor air, drives it through filters and coils, and a fan pushes it out through ductwork to the zones. Every station on that path is something a control system measures, sizes, or holds at setpoint — mixed-air temperature, duct static pressure, the outdoor-air fraction, coil capacity, fan speed. These pages walk the air side end to end, from the air handler out to the VAV box, and give you the tools that put a number on each station.

New to it? Work the six lessons in order — they follow the air from the air handler out to the terminal boxes. Already have a unit in front of you? Jump to the tools: size a duct, average a traverse, work the minimum outdoor air, or check a coil. Everything here is open, needs no login, and tracks nothing.

Start here — the lessons, in order

1 Air Handlers → 2 Economizers → 3 Building Pressure → 4 Unit ID → 5 VAV Systems → 6 Duct Static

The tools

Thirteen field utilities for the air side — measure what a duct is moving, size ducts and coils, work the ventilation math, and predict what a speed change does to a fan. No login, nothing to install.

Measure the air — what's actually moving?

Size ducts & loads

Ventilation & mixing

Coils & psychrometrics

Fans

Related lessons

Two fundamentals the air side leans on — the air-state vocabulary behind every coil calc, and the drive that turns a fan down.