Airflow Requirements
Method 1: Enter CFM Directly
Cubic feet per minute
Method 2: Calculate CFM from HVAC Tonnage
Typical: 400 CFM per ton
Method 3: Calculate CFM from Room Size
Higher for sunny rooms
Duct Parameters
Recommended Duct Sizes
About Duct Sizing
CFM Calculations:
- From HVAC Tonnage: CFM = Tons × 400
- From Room Size: CFM = Square Feet × (1 to 2)
Duct Size Formula: Duct Area = (CFM × 144) / Velocity (FPM)
Recommended Air Velocities:
- Supply Ducts (Main): 700-900 FPM
- Branch Ducts: 500-700 FPM
- Return Air Ducts: 500-700 FPM
Why Proper Sizing Matters: Undersized ducts create noise, pressure drop, and reduced efficiency. Oversized ducts waste money and space while potentially causing poor air distribution.
Quick Reference Guide
Typical HVAC System Sizes:
- 1.5 Ton = 600 CFM (600-900 sq ft)
- 2 Ton = 800 CFM (900-1,200 sq ft)
- 2.5 Ton = 1,000 CFM (1,200-1,500 sq ft)
- 3 Ton = 1,200 CFM (1,500-1,800 sq ft)
- 4 Ton = 1,600 CFM (2,000-2,400 sq ft)
- 5 Ton = 2,000 CFM (2,400-3,000 sq ft)