How many solar attic fans does my home need?

Solar panels on brown roof

A common question we get from consumers: how many solar attic fans do I need to install in order to ventilate my attic properly? 

The answer largely comes down to the size of your attic and the elevation of your home. 

As a general guideline for estimates, homeowners should consider first attic size. This will help you approximate the number of solar attic fans needed. It will also help you figure out which types of fans to install in order to achieve maximum airflow. Bear in mind that different brands of solar attic fans vary in efficiency and size. This may entail different considerations when making estimates. For simplicity, this guide will use iSolar Solutions’ products to help homeowners estimate the ideal number of solar attic fans needed. 

Figuring out your attic’s size

Understanding first the size of your attic plays a critical role. Basic mathematics can help you figure out the size of your home’s attic. Simply multiplying the length and width of your home gives you an approximate estimate of your attic’s size in square feet. The efficiency of solar attic fans depends on measured CFM (cubic feet per minute) of air moved.

Considering the elevation of your home

Is your home a one-storey bungalow, or does it have multiple floors? Is it fully detached? These considerations help in determining how many solar attic fans will be needed to achieve optimal attic ventilation. 

Recommended solar fans based on attic’s size

Here’s a guide on how many solar attic fans your home needs:

For small and medium-sized bungalows

A one-storey bungalow with an attic less than 1,000 sq ft. in size will only need one iSolar 20WSPF-FLEX fan. This fan has a peak efficiency rating of up to 400 CFM.

Slightly larger bungalows between 1,000 sq ft. and 2,000 sq, ft. may require two 20WSPF-FLEX fans. Strategically place these fans on the roof to optimize airflow. Typically, they should be spaced 15 feet apart. 

Larger homes between 1,000-2,000 sq. ft.

An attic of 1,000-2,000 sq. ft. size adds an additional consideration: the number of existing passive vents on your roof. But worry no more as the iSolar 20WSPF-FLEX features scalability, thus easily retrofitted into existing vent holes. 

As mentioned before, it is generally advisable to install multiple small solar attic fans on larger roofs. These fans work best when spaced as far apart as possible (at least 15 feet apart). You can also use larger, more powerful solar attic fan but only one such larger unit would be recommended. In general, smaller, modular units like the 20WSPF-FLEX serves more effectively. 

The number of solar attic fans on any roof should never exceed ⅓ of the number of existing passive vents. Sometimes, the small number of passive vents on a roof does not permit the installation of many smaller fans. In these cases, install a single large fan such as the iSolar 40W-INT fan for best results.

For larger bungalows with attics with 2,000 sq. ft. in size or more, install either two to three smaller 20WSPF-FLEX fans, one to two medium-sized iSolar 18W-INT solar attic fans (rated at 810 CFM), or a single iSolar 40W-INT or 50W-INT fan that can push in excess of 2,000 CFM.

Homes larger than 2,000 sq. ft.

For two-storey homes with attics less than 2,000 sq ft., install either one or two 20WSPF-FLEX fans. Alternatively, a single 18W-INT fan will also work.

For two-storey homes with attics between 2,000-3,000 sq. ft., two or three 20WSPF-FLEX fans, or one to two 18W-INT fans proves to be ideal.

For larger two-storey homes with attics over 2,000 sq. ft in size, install either two to three 18W-INT fans, a single large iSolar 40W-INT fan, or a 50W-INT fan.

Semi-detached homes or townhomes will typically install either one to two 20WSPF-FLEX fans, or a single 18W-INT fan. You can see a full list of these estimates on the FAQ page of iSolar Solutions’ website. 


In iSolar Solutions’ list of products, you will find our fans classified as either MOD or INT fans, and you may wonder what these designations mean. 

MOD stands for modular. It means that this fan can be coupled with a second fan if an attic requires additional airflow. MOD fans provide medium-capacity airflow and feature adjustable solar panels to best capture the sun’s rays. They also cost relatively less than INT fans. 

In contrast, INT fans stands for integrated. These one-piece units weigh much heavier but also much more powerful. INT fans like the 40W-INT or 50W-INT, unlike modular, requires installation in a central position on the roof. An iSolar Solutions representative can help you figure out which of these options perfectly suits your home. 

Get an accurate estimate

Achieving optimal airflow in your home’s attic requires an intricate knowledge of building science and roof design. The information presented here generally intends to guide homeowners to estimate the cost of installing solar attic fans. To find out more about what solar attic fan solutions fits your home, please contact the experts at iSolar Solutions for more information.

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