Air Return Intakes Sizes Capacities

Reference data and engineering information about air return intakes sizes capacities for gases and compressed air applications.

airreturnintakessizes

Overview

Engineering reference data for Air Return Intakes Sizes Capacities in gases and compressed air.

Key Formulas

Ideal Gas Law

$PV = nRT$

Pressure × Volume = moles × gas constant × temperature.

Boyle's Law

$P_1 V_1 = P_2 V_2$

At constant temperature.

Charles's Law

$\frac{V_1}{T_1} = \frac{V_2}{T_2}$

At constant pressure.

Variables

Symbol	Description	Unit
$P$	Pressure	Pa
$V$	Volume	m³
$T$	Temperature	K
$R$	Gas constant	8.314 J/(mol·K)

Return Intake Capacities

The following table provides approximate air handling capacities for standard return intake sizes:

27 rows

Air return intake nominal sizes and approximate capacities
size
10 × 4
10 × 5
10 × 6
10 × 8
12 × 4
12 × 5
12 × 6
12 × 8
12 × 10
14 × 4
14 × 5
14 × 6
14 × 8
24 × 4
24 × 5
24 × 6
24 × 8
24 × 10
24 × 12
30 × 4
30 × 5
30 × 6
30 × 8
30 × 10
30 × 12
30 × 14
30 × 16

Source: engineeringtoolbox.com

Screen Efficiency

Installing insect or bird screens on return intakes reduces the free intake area. When sizing intakes with screens, apply the following efficiency factors:

Screen Type	Free Area
1/2" mesh screen	90%
1/4" mesh screen	80%
Insect screen	50%

To calculate the effective capacity with a screen installed, multiply the nominal capacity by the free area percentage:

$Q_{\text{effective}} = Q_{\text{nominal}} \times \text{Free Area Factor}$

For example, a 24 × 12 intake (795 cfm nominal) with an insect screen would provide approximately $795 \times 0.50 = 398$ cfm effective capacity.

References

Original Source

Source: engineeringtoolbox.com