# How Many Solar Attic Fans Do I Need?

Written By: | Last Updated on: June 28, 2023

Are you tired of a hot and stuffy attic? Installing solar attic fans could be the solution you need for proper attic ventilation. But how many solar attic fans do you need for your home?

The answer depends on various factors such as attic size, slope, and intake vents.

As a general rule of thumb, for every 500 to 1,000 square feet of attic space, you need one solar attic fan with an 800 CFM (cubic feet per minute) capacity. However, this number may vary depending on your specific situation.

And in this article, I will guide you step by step through the process of calculating the appropriate number of solar attic fans for your home.

## Key Takeaways

• To calculate the number of solar attic fans needed for your home, you need to determine your attic’s size, slope, and existing intake air vents
• Measure your attic’s length and width to calculate the total area in square feet.
• Find out your attic’s slope or pitch by measuring the horizontal and vertical distances of a roof rafter
• Consider the intake air vents by identifying the existing vents, measuring their size and type, and calculating the required intake vent area using the 1:300 rule recommended by the International Residential Code (IRC)
• To determine the total number of solar attic fans needed, refer to the tables provided for low, medium, and high attic slopes, which show the approximate number of solar attic fans for different attic sizes
• Solar attic fans offer many benefits, such as energy efficiency, improved attic ventilation, extended roof lifespan, increased home comfort, and eco-friendliness

## How to Calculate the Number of Solar Attic Fans for Your Home?

### 1. Figure out Your Attic’s Size

Determining the appropriate number of solar attic fans for your home requires precisely calculating your attic’s size.

Begin by measuring your attic’s length and width.

Arm yourself with a tape measure and carefully take note of the entire attic space, including any irregularities, obstructions, or variations in layout.

If your attic has an unusual shape or is divided into sections, measure each area separately and combine their measurements later.

For instance, imagine your attic is L-shaped. You’ll need to measure both sections of the L-shape individually, and then add their areas together to find the total attic area.

Once you’ve measured the length and width of your attic or its sections, you can calculate the total area in square feet.

Simply multiply the length by the width for each section, and add the areas together if there are multiple sections.

Let’s assume your attic has a length of 40 feet and a width of 30 feet

To calculate the area, you would multiply 40 feet by 30 feet, resulting in an attic area of 1,200 square feet.

### 2. Find out Attic Slope or Pitch

The slope or pitch refers to the angle of the roof, which directly impacts the amount of heat and air circulation in the attic.

A steeper roof pitch may result in a larger volume of air that requires more efficient ventilation. Here’s how you can find out your attic’s slope or pitch:

#### Step 1: Locate a Roof Rafter

First, you’ll need to locate a roof rafter in your attic. Rafters are the sloped wooden beams that make up the roof’s structure.

They extend from the highest point of the roof down to the eaves. You’ll be measuring the angle of one of these rafters to determine the slope or pitch of your attic.

#### Step 2: Measure the Horizontal and Vertical Distances

With a tape measure, take two measurements on the rafter: the horizontal distance (also called the “run”) and the vertical distance (also called the “rise”).

To measure the horizontal distance, hold the tape measure flat against the rafter and measure from one end of the rafter to the other.

For the vertical distance, measure the distance from the highest point of the rafter to the lowest point where the rafter meets the floor or the attic joists.

For example, let’s say you measured a horizontal distance of 12 inches and a vertical distance of 6 inches

This means that for every 12 inches of horizontal distance, the roof rises by 6 inches.

#### Step 3: Calculate the Roof Pitch

To find the roof pitch, divide the vertical distance (rise) by the horizontal distance (run).

Using the measurements from our example, you would divide 6 inches (rise) by 12 inches (run), resulting in a roof pitch of 0.5.

Alternatively, you may express the roof pitch as a ratio, such as 6:12 or 6-in-12

This indicates that for every 12 inches of horizontal distance, the roof rises by 6 inches vertically.

In general, roof pitches can vary significantly, with common values ranging from 4:12 (moderate slope) to 12:12 (steep slope).

### 3. Consider the Intake Air Vents

Factoring in the intake air vents when determining the number of solar attic fans will help to know the proper balance of intake and exhaust vents.

To do this, inspect your attic to identify the existing intake air vents.

Typically, these vents are located along the soffit or eaves of your roof.

There are different types of intake air vents, including continuous soffit vents, individual soffit vents, and gable vents.

Then take note of the size and type of each vent, as well as their positioning.

Measure the width and height of each vent and calculate the total vent area by multiplying the width by the height.

For example, if you have 4 individual soffit vents, each measuring 6 inches by 12 inches, the total vent area would be 288 square inches (4 vents x 6 inches x 12 inches).

Next, calculate the required intake vent area for proper attic ventilation using the 1:300 rule recommended by the International Residential Code (IRC)

This rule states that for every 300 square feet of attic space, there should be 1 square foot of vent area split between intake and exhaust vents.

Divide your attic area by 300 to find the required vent area.

Using a previously calculated attic area of 1,200 square feet as an example, you would get 4 square feet (1,200 square feet ÷ 300)

Since this area is split between intake and exhaust vents, you will need 2 square feet of intake vent area and 2 square feet of exhaust vent area.

Convert the required intake vent area from square feet to square inches by multiplying by 144 (2 square feet x 144 = 288 square inches)

In this example, the required intake vent area is 288 square inches.

Finally, compare your existing intake vent area to the required intake vent area calculated in the previous step.

If your existing vent area is sufficient or larger than the required intake vent area, your current intake air vents should provide adequate airflow for your solar attic fans.

However, if your existing intake vent area is smaller than the required intake vent area, you may need to consider adding or enlarging intake air vents to ensure optimal attic ventilation.

Improperly sized or positioned intake air vents can negatively impact the efficiency of your solar attic fans and the overall attic ventilation system.

### 4. Find the Total Number of Solar Attic Fans

Now that you have all the necessary information, you can determine the total number of solar attic fans needed for your home.

Here are three separate tables for low, medium, and high attic slopes.

Each table shows the approximate number of solar attic fans for different attic sizes, assuming each fan has an 800 CFM capacity.

a. For Low Slope Roofs (1/12 – 2/12):

b. For Medium Slope Roofs (3/12 – 6/12):

c. For High Slope Roofs (7/12 – 12/12):

## What Are the Benefits of the Solar Attic Fans?

Solar attic fans are a sustainable and eco-friendly solution for improving attic ventilation. Here are some benefits of using solar attic fans:

• Energy Efficiency: Solar attic fans operate on solar energy, making them an energy-efficient solution for attic ventilation. They don’t require any electricity to run, which helps to reduce your overall energy consumption and lower your energy bills
• Improved Attic Ventilation: Solar attic fans help to improve attic ventilation by circulating the air and reducing excess moisture, which can lead to mold growth, roof damage, and poor indoor air quality
• Extended Roof Lifespan: Solar attic fans protect your roof from heat damage, which can lead to premature aging and reduce its lifespan. By reducing heat buildup, they can help to maintain your roof’s integrity and prevent costly repairs or replacements
• Increased Home Comfort: They make your home feel fresher and more comfortable by removing hot and humid air from the attic, which can lead to lower indoor temperatures and reduced strain on your air conditioning system
• Environmentally Friendly: Solar attic fans operate on renewable solar energy, reducing your carbon footprint and reliance on traditional energy sources. They also do not produce greenhouse gas emissions, making them an eco-friendly option for homeowners

## FAQs

### Are Solar-Powered Attic Fans Worth It?

Solar-powered attic fans are worth it as they can reduce energy costs and prolong roof lifespan.

### How Do You Size a Solar Attic Fan?

You size the solar attic fan depending on the attic size and the attic slope or pitch.

### Where Should I Place My Solar Attic Fan?

You should place the solar attic fa near the peak of the roof and as close to the center of the attic as possible for optimal ventilation.

## Conclusion

As promised, we’ve covered the process of calculating the number of solar attic fans needed for your home.

By measuring your attic’s size, determining its slope, and factoring in the intake air vents, you can determine the appropriate number of solar attic fans for optimal ventilation.

And if you ask me, I’d recommend you turn all your home appliances solar-powered for more sustainable and efficient living

Kami Turky
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