Circular Ducts

Reference data and engineering information about circular ducts for hvac systems applications.

circularducts

Overview

Engineering reference data for Circular Ducts in HVAC systems.

Key Formulas

Sensible Heat

$Q = \dot{m} c_p \Delta T$

Heat causing temperature change.

Latent Heat

$Q = \dot{m} h_{fg} \Delta\omega$

Heat causing moisture change.

COP (Cooling)

$COP = Q_c / W$

Coefficient of performance.

Variables

Symbol	Description	Unit
$Q$	Heat transfer	W
$\dot{m}$	Mass flow rate	kg/s
$c_p$	Specific heat of air	J/(kg·K)
$\Delta T$	Temperature difference	K

Circular Duct Specifications

Metric Dimensions

The following table provides standard metric dimensions for circular ductwork used in air handling and ventilation systems.

14 rows

Standard circular duct dimensions in metric units (mm).
Nominal Diameter(mm)	Outside Diameter(mm)	Inside Diameter(mm)
63	63 - 63.5	61.8 - 62.3
80	80 - 80.5	78.8 - 79.3
100	100 - 100.5	98.8 - 99.3
125	125 - 125.5	123.8 - 124.3
160	160 - 160.6	158.7 - 159.3
200	200 - 200.7	198.6 - 199.3
250	250 - 250.8	248.5 - 249.3
315	315 - 315.9	313.4 - 314.3
400	400 - 401.0	398.3 - 399.3
500	500 - 501.1	498.2 - 499.3
630	630 - 631.2	628.1 - 629.3
800	800 - 801.6	798.0 - 799.3
1000	1000 - 1002.0	997.9 - 999.3
1250	1250 - 1252.5	1247.8 - 1249.3

Source: engineeringtoolbox.com

Imperial Dimensions & Weights

This table shows galvanized steel duct dimensions, surface areas, and weights for different sheet metal gages in imperial units.

7 rows

Galvanized steel duct properties in imperial units. Weight increases with lower gage numbers (thicker material).
Diameter(inches)	Surface Area(ft²/ft)	Gage 26 Weight(lbs/ft)	Gage 24 Weight(lbs/ft)	Gage 22 Weight(lbs/ft)
4	1.05	1.02	1.36	1.59
5	1.31	1.25	1.67	1.95
6	1.57	1.49	1.98	2.32
7	1.83	1.72	2.3	2.69
8	2.09	1.96	2.61	3.06
9	2.36	2.2	2.93	3.42
10	2.62	2.51	3.34	3.91

Source: engineeringtoolbox.com

Key Properties

Surface Area: The surface area per linear foot ( $ft^2/ft$ ) is critical for calculating friction losses, insulation requirements, and material costs.
Gage Thickness: Lower gage numbers indicate thicker sheet metal. For example, Gage 22 ( $0.0299$ inches) is thicker than Gage 26 ( $0.0179$ inches), providing greater structural strength and durability.
Weight Variation: Weight increases with both duct diameter and decreasing gage number (increasing thickness).

Interactive Charts

Air Ducts - Sizing

References

Original Source

Source: engineeringtoolbox.com