Guide to Air Vents for Whole House Fans

When you close up your home, whether for the night or for the entire summer, you seal your house from the outside air. If you are running the air conditioner, this ensures that the cool air created by the machine is not wasted. But a closed house can also create problems for air quality.

Summer days can trap air in your home and your attic, creating a heating effect that can be expensive (and slow) to cool with air conditioners.

So if you close up the house, you expose yourself to indoor air pollution, but if you open the home, you’re letting in hot air. Is there a better solution?

Whole house fans, which are different from attic fans and powered attic ventilators, are an innovative way to cool the home while allowing for high-quality circulation. A whole house fan cools your home by pushing out hot, stale air and bringing in fresh, cool air. Instead of recirculating, it brings in new air, reducing indoor pollution while making a more comfortable space.

But to achieve this goal, you need proper air vents for whole house fans.

whole house fan for home

What are Whole House Fans?

Whole house fans are a surprisingly simple yet effective way to cool your home. Essentially, they are fan units, much like a very strong box fan, that is placed in the ceiling of your home’s top level, on the floor of your attic. They are not placed in the roof or attic wall like an attic fan. In this position, it pulls air from the living space and blows it into the attic, creating a gentle yet noticeable ventilation of fresh air in your home.

Whole-house fans are a cost effective tool for cooling the house, but they are not ideal for extremely hot days or in humid environments.

When the temperature outside is extremely hot, a whole house fan will simply pull hot air into the home; it doesn’t cool the air like an air conditioning unit. According to Green Building Advisor, a whole house fan is best used when the temperature is less than 80 degrees; any more than that and the cooling effects of a whole-house fan is not realized in the home.

Certain regions will also benefit more from a whole-house fan than others. Generally, locations with hot, dry summer days and cool nights benefit the most, so regions in the North, West and Southwest of the country will generally benefit more.

From roughly Maine to Pennsylvania, and west from California to Washington, you will notice more of a benefit when you have a whole house fan in your home. Other regions will be able to use them, but the benefits will be less frequent. For example, Arizona can be too hot for a whole-house fan unless it cools down at night. Regions where it is hot and humid like Florida are not optimal for a whole house system.

By creating ventilation, a whole-house fan is also able to reduce indoor air pollution. This is because indoor air pollution steadily increases if there is no flow of air. Air pollution from candles, air fresheners, mold, pets, and dust mites are gradually created or released in the home, and when the house is completely shut, either in the summer or the winter, these airborne contaminants have no place to go.

By using a whole-house system, you allow the air to flow from the bottom of the house, through the attic floor, and out air vents in the attic walls and ceiling. This movement will ensure that airborne contaminants are not allowed to become overly concentrated.

attic vent in home

Why Do You Need Vents?

Whole house fans create a flow of air through the home, but in order to achieve this effect, there needs to be a way for air to come in, and a place for air to go out. To go outward, you need vents in the attic.

But first, let’s start at the bottom. For effective air flow, there needs to be a source of air, this air is brought in through open windows or doors (assuming there is a screen door, of course). Therefore, to function properly, you need to keep windows open on the ground floor, which will allows the fresh, natural air to flow inward.

As the air moves through the home, it will collect contaminants while creating a gentle, cooling breeze of fresh air. It will travel through the home until it is eventually sucked through the whole-house fan. Once it passes through the fan, it is in the attic.

But where can it go from there?

Now it will leave the attic through vents, which allow the air to escape. Without vents, pressure will build up in the attic causing a lot of stress to the fan.


How Much Ventilation Space Do You Need?

As we’ve described, to work properly an attic fan needs the right amount of ventilation. As the power of the fan goes up, it will be moving more air; therefore, more powerful whole-house fans will need more available ventilation to work properly.

The required power of your whole-house fan is determined by the overall air volume of the home, and the ventilation requirements is determined by the fan’s power. Therefore, in an indirect way, the ventilation requirements are determined by the air volume of the home.

Here’s how you can find the required attic venting for a whole-house fan…


Calculate the Air Volume

Start by measuring the overall air volume of the living space in your home. Measure the length and width of the house and use these measurements to calculate the square footage of each floor. If you have a perfectly square or rectangular home, you can simply multiply the width and the length to get the total square footage. Now that you have the overall floor area, simply multiply that number by the height of the house. You now have a calculation for the air space in your home, but you still have some numbers to crunch.


Measure the Cubic Feet Per Minute (CFM)

You can now use the air volume to measure the cubic feet per minute. Take the air volume total and multiply it by 30, which represents a complete air change every other minute. (If it was every minute, you would multiply by 60.) Now take that number and divide by 60 to get your Cubic Feet per Minute, or “CFM,” which is the power you’ll need from your whole-house fan.


Determine Attic Ventilation

You will now need to determine your attic vent size. You will need at least one square foot of vent space for every 750 CFM. So if you have, for example, a CFM of 6,000, you’ll need at least eight square feet of ventilation, which will ensure the right amount of air flow through your home. If this is the case, you could go with a single 3-foot by 3-foot vent, which would give you nine square feet of ventilation, more than enough to ensure a cooling, cleaning breeze in your home.


Do You Need Maintenance for Whole Home Fans?

While most whole house fans are sturdy, reliable machines, you may need to perform some basic maintenance and cleaning to keep them running properly.

Dusting is one of the most important chores you can do to maintain your fan. Over the months, your fan blades will inevitably collect a lot of dust. Cleaning the blades, however, can extend your fans life and allow it to function with greater effectiveness and efficiency. Once a season, unplug the fan and use a damp cloth to wipe away any accumulated dust. You can also use a mild cleaning product to help the cleaning process. Wipe down both sides of each blade, and make sure to clean the motor and casing.

With this simple chore, done once a year, you can prolong the effectiveness of your whole house fan.


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