What Size Whole House Fan Do I Need: Choose The Right Size Whole House Fan!

A whole house fan can be an efficient and cost-effective way to cool a home, especially during the evening hours when outdoor temperatures drop.

This device pulls cool air in through windows while pushing out the hot air trapped in the attic.

But to optimize its effectiveness, you need to choose the right size.

Follow this guide to learn everything you need to succeed in your endeavor.

What Size Whole House Fan Do I Need & The Answer!

The Basics

Before we delve into sizes, it’s important to grasp two main concepts:

CFM: This stands for cubic feet per minute and represents the volume of air the fan moves. It’s the primary metric used to measure the capacity of a whole house fan.

Air Changes Per Hour (ACH): The number of times all the air in your home is replaced in an hour. For whole house fans, a common recommendation is 3-4 ACH.

Calculate Your Home’s Volume

Start by determining the cubic footage of your living space.


For multi-story homes, calculate the volume for each story and add them together.

Determine the Needed CFM

Once you know the volume, you can compute the CFM.

Required CFM=Volume of the house×ACH

For instance, if your home is 30,000 cubic feet and you want 3 ACH, then:

Required CFM=30,000×3=90,000

So, you’d need a fan with a capacity of 90,000 CFM.

Consider Other Factors

Home Layout: If your home has a lot of separate rooms or partitions, you might need a slightly more powerful fan to ensure adequate airflow.

Local Climate: In very hot or humid areas, a higher capacity fan might be more effective.

Intake Area: Ensure that your home has enough intake vent area (usually through windows) to allow for the incoming air. A general rule is that for every 750 CFM, you should have 1 square foot of intake vent area.

Energy Efficiency and Noise Levels

While larger fans can move more air, they also consume more energy and might produce more noise.

Always check for the energy rating and opt for fans that use brushless motors as they tend to be quieter and more efficient.

Professional Assessment

While the steps above give you a general idea, consulting with a professional can be beneficial.

They can evaluate other nuances like the quality of insulation, and the number of windows.

The direction your home faces, and more to recommend the perfect size.


Q1# What does CFM stand for in relation to whole house fans?

CFM stands for Cubic Feet per Minute, which indicates the volume of air the fan can move in a minute.

It’s the primary metric used to measure the capacity of a whole house fan.

Q2# How do I calculate the volume of my home?

To calculate the volume of your home, multiply its length by its width and then by its height.

For homes with multiple stories, compute the volume for each story separately and then sum them.

Q3# What is Air Changes Per Hour (ACH), and how does it impact fan size?

ACH represents how many times the air in your home is replaced in an hour.

For whole house fans, a typical recommendation is 3-4 ACH.

To determine the needed CFM, multiply the home’s volume by the desired ACH.

Q4# Do I need to consider other factors besides CFM and ACH when choosing a fan size?

Yes, it’s essential to account for factors like the layout of your home, local climate, and intake vent area.

For example, homes with many separate rooms may require a more powerful fan for effective airflow.

Q5# Can a fan that’s too big for my home be a problem?

While a larger fan can cool your home faster, it might also consume more energy, produce more noise, and lead to overcooling.

It’s crucial to choose a fan size that’s optimized for your home’s specific needs.

Q6# Is it advisable to consult a professional when choosing a whole house fan size?

Yes, consulting with a professional can provide a more accurate assessment.

They can consider various nuances, such as insulation quality, and the number of windows.

The orientation of your home, to recommend the most suitable fan size.

Final Words

Selecting the right size whole house fan is crucial for efficiency and comfort.

By considering your home’s volume, desired air changes, and other unique factors, you can find the best fit for your needs.

Remember, while it’s good to have an idea of what you need, a professional assessment can provide clarity and peace of mind.

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