Attic Fan Size Calculator
This attic ventilation calculator computes the size and number of solar powered attic fans to achieve the proper ventilation for your attic. The Home Ventilation Institute (www.hvi.org) recommends that powered attic ventilators provide a minimum of 10 air volume changes per hour.
Step 1. Calculate the required CFM (air flow)
Method A: I know the dimensions of my attic space. (more accurate)
Method B: I don't know the dimensions of my attic space.
Attic Fan Size Calculator
Step 2. Use the chart below as an attic vent fan CFM calculator.
Solar Royal (shop)
| Required CFM | Num Fans / Size |
Min. Soffit Area* (sq in) |
|---|---|---|
| up to 1825 | (1) / 35 Watt | 925 |
| 1826 to 3650 | (2) / 35 Watt | 1850 |
| 3651 to 5475 | (3) / 35 Watt | 2775 |
| 5476 to 7300 | (4) / 35 Watt | 3700 |
ATTIC BREEZE (shop)
| Required CFM | Num Fans / Size |
Min. Soffit Area* (sq in) |
|---|---|---|
| up to 1550 | (1) / 25 Watt | 750 |
| 1551 to 1775 | (1) / 35 Watt | 925 |
| 1776 to 1925 | (1) / 45 Watt | 1025 |
| 1926 to 3100 | (2) / 25 Watt | 1500 |
| 3101 to 3550 | (2) / 35 Watt | 1850 |
| 3551 to 3850 | (2) / 45 Watt | 2050 |
| 3851 to 4650 | (3) / 25 Watt | 2250 |
| 4651 to 5325 | (3) / 35 Watt | 2775 |
| 5326 to 5775 | (3) / 45 Watt | 3075 |
*Note: Adequate intake area is essential to ensure proper
operation of your powered attic vent fan and to avoid attic.