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Ubify Media & Design Operations
UI/UX & DIGITAL MEDIA SPECIALISTS
About This Tool
Undersized HVAC ducts choke airflow, increase electric compressor head pressure, and generate loud air turbulence whistle. This tool computes optimal round duct diameter and equivalent rectangular sheet metal aspect ratios following ACCA Manual D friction chart formulas.
How to Use
- 1
Enter design room airflow in CFM (typically 400 CFM per 1 Ton of cooling capacity).
- 2
Enter friction rate per 100 feet (standard residential target is 0.08 in. w.g. per 100 ft).
- 3
Review calculated round duct diameter and air velocity in Feet Per Minute (FPM).
- 4
Select from equivalent rectangular sheet metal dimensions (8″, 10″, or 12″ height profiles).
Frequently Asked Questions
What is the maximum recommended duct velocity in residential homes?
For branch supply runouts leading to bedrooms and living spaces, air velocity should stay below 600 to 700 FPM to prevent register air noise. Main trunk ducts can run at 700 to 900 FPM.
How many CFM is required per ton of AC?
Standard residential split systems require approximately 350 to 450 CFM of airflow per ton of nominal refrigeration capacity (12,000 BTU/hr), with 400 CFM/ton being the universal design benchmark.