Side-by-Side Comparison
Structural & HVAC
HVAC Duct Sizes vs. Structural Steel Shapes
Comparing 2 standards across 18 specifications. 18 key differences identified.
Comparing:
HVAC Duct Sizes
Structural Steel Shapes
Standard residential and commercial HVAC duct dimensions are specified by round spiral diameter (4 to 20 inches) and equivalent rectangular cross-sections based on airflow capacity (CFM) at 0.10 inches water column friction loss per 100 feet.
AISC structural steel profiles standardize hot-rolled structural members including Wide Flange I-Beams (W-Shapes e.g. W8×10 = 8" nominal depth, 10 lb/ft), American Standard Beams (S-Shapes), Channels (C-Shapes), Hollow Structural Sections (HSS), and Angles (L-Shapes).
Specification Comparison Table
18 Parameters| Parameter / Spec | ||
|---|---|---|
|
Governing Standards
|
SMACNA / ACCA Manual D Residential Duct Systems | AISC 360 / ASTM A6/A6M / ASTM A992 (Grade 50 steel) |
|
Standard Sizing Metric
|
Cubic Feet per Minute (CFM) at 0.10" w.g. / 100 ft friction rate (Residential) / 0.08" (Quiet) | — |
|
4" Round Duct
|
Capacity: ~30 CFM | Small bathrooms, range hood make-up air | — |
|
5" Round Duct
|
Capacity: ~50 CFM | Small powder rooms, walk-in closets | — |
|
6" Round Duct (Standard Branch)
|
Capacity: ~100 CFM | Standard 10×12 ft bedrooms | — |
|
7" Round Duct
|
Capacity: ~150 CFM | Master bedrooms, medium living areas | — |
|
8" Round Duct
|
Capacity: ~200 CFM (0.5 Ton A/C) | Large master suites, kitchens | — |
|
10" Round Duct
|
Capacity: ~350 CFM (~1.0 Ton A/C) | Open living rooms, main branches | — |
|
12" Round Duct
|
Capacity: ~550 CFM (~1.5 Ton A/C) | Main trunk lines | — |
|
14" Round Duct
|
Capacity: ~800 CFM (2.0 Ton A/C) | Main central supply trunk | — |
|
Airflow Rule of Thumb
|
1 Ton of Air Conditioning = 400 CFM of airflow | — |
|
W-Shape Designation Code
|
— | W [Nominal Depth in Inches] × [Weight in Pounds per Linear Foot] |
|
W8 × 10 (Residential Light Beam)
|
— | Depth: 7.89 in (200 mm) | Flange Width: 3.94 in | Weight: 10.0 lb/ft | Area: 2.96 sq in |
|
W8 × 18 (Standard Basement Beam)
|
— | Depth: 8.14 in (207 mm) | Flange Width: 5.25 in | Weight: 18.0 lb/ft | Area: 5.26 sq in |
|
W10 × 22 (Common Floor Girder)
|
— | Depth: 10.17 in (258 mm) | Flange Width: 5.75 in | Weight: 22.0 lb/ft | Area: 6.49 sq in |
|
W12 × 26 (Heavy Residential / Light Comm)
|
— | Depth: 12.22 in (310 mm) | Flange Width: 6.49 in | Weight: 26.0 lb/ft | Area: 7.65 sq in |
|
HSS (Hollow Structural Sections)
|
— | Square & Rectangular structural tubing e.g. HSS 4×4×1/4 (4" sq, 0.25" wall, 12.21 lb/ft) |
|
Equal Leg Angle (L-Shape)
|
— | L [Leg 1] × [Leg 2] × [Thickness] e.g. L 3×3×1/4 (Lintel / Bracing) |