Side-by-Side Comparison
Structural & HVAC
HVAC Duct Sizes vs. Rebar Sizes
Comparing 2 standards across 19 specifications. 19 key differences identified.
Comparing:
HVAC Duct Sizes
Rebar Sizes
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.
Standard reinforcing steel bar (rebar) sizes under ASTM A615 are designated by number sizes #3 through #18 representing the nominal diameter in eighths of an inch (e.g. #4 rebar = 4/8" = 1/2" / 12.7 mm diameter, weighing 0.668 lb/ft).
Specification Comparison Table
19 Parameters| Parameter / Spec | ||
|---|---|---|
|
Governing Standards
|
SMACNA / ACCA Manual D Residential Duct Systems | ASTM A615 / ASTM A706 (Earthquake grade) / CSA G30.18 |
|
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 | — |
|
US Numbering System
|
— | Rebar number = diameter in 1/8ths of an inch (e.g. #5 = 5/8" / 15.875 mm) |
|
#3 Rebar (Driveway / Patio Mesh)
|
— | Dia: 0.375 in (9.525 mm) | Area: 0.11 sq in | Weight: 0.376 lb/ft (0.560 kg/m) |
|
#4 Rebar (Residential Footings / Walls)
|
— | Dia: 0.500 in (12.70 mm) | Area: 0.20 sq in | Weight: 0.668 lb/ft (0.994 kg/m) |
|
#5 Rebar (Structural Slabs / Foundation)
|
— | Dia: 0.625 in (15.88 mm) | Area: 0.31 sq in | Weight: 1.043 lb/ft (1.552 kg/m) |
|
#6 Rebar (Retaining Walls / Beams)
|
— | Dia: 0.750 in (19.05 mm) | Area: 0.44 sq in | Weight: 1.502 lb/ft (2.235 kg/m) |
|
#8 Rebar (Commercial Columns)
|
— | Dia: 1.000 in (25.40 mm) | Area: 0.79 sq in | Weight: 2.670 lb/ft (3.973 kg/m) |
|
#18 Rebar (High-Rise Core Columns / Dams)
|
— | Dia: 2.257 in (57.33 mm) | Area: 4.00 sq in | Weight: 13.60 lb/ft (20.24 kg/m) |
|
Standard Steel Grades
|
— | Grade 40 (40 ksi / 280 MPa), Grade 60 (60 ksi / 420 MPa), Grade 75 (75 ksi / 520 MPa) |