What You’ll Learn:

• The Scale Problem in Ductwork
• Why duct sizing isn’t as simple as it seems
• How cross-sectional area dramatically impacts airflow

Understanding Pressure (The “David Bowie” Connection)

• Static pressure vs. velocity pressure vs. pressure loss vs. external static pressure
• Why pressure isn’t the “bad guy”—friction is
• The asteroid analogy: how friction affects airflow like atmospheric entry

Visual Demonstrations

• The “used car lot” inflatable tube demo showing static and velocity pressure balance
• Bathroom scale and crate analogy for understanding energy transfer
• How energy gets “used” vs “wasted” in duct systems

Measuring Airflow

• The 40¢ manometer: building pressure measurement tools with basic tubing
• Why we focus on static pressure measurements in residential HVAC
• Pitot tube basics and velocity pressure measurement challenges

Residential vs Commercial Design Philosophy

• Why residential design works “backwards” from commercial
• The myth of the 0.08 “magic number” and why there isn’t one universal answer
• How to calculate proper friction rates based on available static pressure

Real-World Applications

• Why 0.1 inches of water column per 100 feet doesn’t work in modern systems
• The impact of modern filters, coils, and unit locations on system design
• Central air vs “corner air”—the importance of equipment placement

Modern Challenges

• How today’s tighter coils, better filters, and larger homes have changed the game
• Why oversized equipment on undersized ducts seems to “work” (but shouldn’t)
• The importance of using tools like TrueFlow grids instead of relying on customer satisfaction

Key Takeaways:

• Duct sizing is geometric, not linear—small changes have big impacts
• Friction is your enemy, not pressure
• Modern residential systems need larger ducts than traditional 0.1 sizing allows
• Equipment placement dramatically affects duct sizing requirements
• Proper measurement and testing beats customer complaints as success metrics