How To Calculate CFM of Solar Attic Fans

To calculate the CFM (Cubic Feet per Minute) of a solar attic fan, you typically need to consider the size of the attic space, the desired air exchanges per hour, and the efficiency of the fan. Here's a general method to calculate it:

1. Measure the attic space: Determine the length, width, and height of your attic in feet. Multiply these dimensions to get the volume of the attic in cubic feet.

2. Determine the desired air exchanges per hour: This depends on factors such as the climate in your area, the attic insulation, and the level of ventilation needed to maintain a comfortable temperature. A common recommendation is to aim for 8 to 10 air exchanges per hour for optimal ventilation.

3. Calculate the required CFM: Multiply the volume of the attic by the desired air exchanges per hour, then divide by 60 (to convert hours to minutes). This gives you the CFM needed to achieve the desired air exchanges per hour.

4. Consider the efficiency of the solar attic fan: Solar attic fans come with a specified CFM rating. Make sure the fan you choose meets or exceeds the CFM calculated in step 3.

For example, if your attic measures 20 feet long, 15 feet wide, and 8 feet high (a total of 2,400 cubic feet), and you want to achieve 10 air exchanges per hour:

Volume of attic = 20 ft * 15 ft * 8 ft = 2,400 cubic feet Desired air exchanges per hour = 10 CFM required = (2,400 * 10) / 60 = 400 CFM

So, you would need a solar attic fan with a CFM rating of at least 400 to achieve the desired ventilation.