Standard Rectangular Duct Sizes

The table is based on the ducts friction loss formula.

Standard rectangular duct sizes.

Sizing is based on airflow needs per cubic foot per minute as well as velocity. Flexible duct work must be stretched tightly for maximum air flow. A 0 to 400 cfm fan requires a 4 inch minimum duct size but a 6 inch duct is recommended. In order to maintain velocity reduce duct size.

The minimum duct sizes and recommended duct sizes based on a hood fan s cfm rating are as follows. Equivalent diameter rectangular and circular hvac ducts equivalent diameter for rectangular and circular ducts air flows between 100 50000 cfm maximum size of duct or pipe through steel joists k series joists and maximum size of ducts and pipes. The table below can be used to compare equivalent diameters for rectangular and round circular ducts. Rectangular or square ducting comes in standard sizes ranging from 3 by 7 inches to 35 by 40 inches.

The length of the rectangular duct size would range from 0 7mm to 0 9mm galvanised mild steel depending on size. In addition its flexibility allows for easier installation in hard to reach areas. Use insulated duct or duct board in unheated spaces. They are as follows.

The master flow 36 in. Wrap around duct l shape duct all sizes shall be listed using outside. Rectangular ductwork is manufactured in three different styles. Master flow 14 in.

The equivalent diameter is the diameter of a circular duct or pipe that gives the same pressure loss as an equivalent rectangular duct or pipe. Galvanized steel flat sheet can be cut to size for a tough hvac job that requires a customized fitting. Design cfm 4 cfm 6 cfm 8 cfm 10 cfm 12 60 6x4 60 4x6 90 4x8 120 4x10 150 4x12 90 8x4 110 6x6 160 6x8 215 6x10 270 6x12 120 10x4 160 8x6 230 8x8 310 8x10 400 8x12 150 12x4 215 10x6 310 10x8 430 10x10 550 10x12 180 14x4 270 12x6 400 12x8 550 12x10 680 12x12 210 16x4 320 14x6 490 14x8 670 14x10 800 14x12 240 18x4 375 16x6 580 16x8 800 16x10 950 16x12 270 20x4 430 18x6 670 18x8 930 18x10 1100. Sealant is available in the seams upon request.

Ductwork is fabricated with either snap lock or pittsburgh longitudinal seams. For screen reader problems with this website please call 1 800 430 3376 or text 38698 standard carrier rates apply to. Provided here is the rectangular duct sizes chart for your personal reference and this chart table shows the duct size cfm and their equivalent diameter in inches. Duct work is otherwise called as duct system.

Flexible duct can be installed in place of galvanized pipe in many applications if allowed by your local hvac codes. Last take off run to be located 12 18 from end. Half section rectangular duct model rd14x8x48. The rectangular dimensions and the air flow volume are adapted to the equal friction loss.

Always stagger take off ducts by 12 to maintain pressure. The hvac model that you re interested in should offer information regarding the maximum airflow per cubic foot per minute or cfm to help you determine adequate.