When using a whole house fan, it’s important to open the right number of windows in your home. Opening too few windows won’t allow for proper air circulation. Opening too many may reduce the cooling efficiency of the fan. So what’s the sweet spot? Let’s take a look at some key factors to consider.
Page Contents
- 1 What is a Whole House Fan?
- 2 Key Factors That Determine How Many Windows to Open
- 3 Recommended Number of Windows to Open
- 4 What Happens When You Open Too Many or Too Few Windows?
- 5 Use Caution When Temperatures are High Outdoors
- 6 Consider Getting a Whole House Fan with a Higher CFM
- 7 Use Window Fans to Supplement Air Intake
- 8 Install More Roof Vents for Air Exhaust
- 9 Conclusion
What is a Whole House Fan?
A whole house fan (WHF) is a large fan designed to cool your entire home by pulling air in through open windows and exhausting it out through the attic. This creates a cooling breeze and reduces the temperature inside the house. Whole house fans are installed in the ceiling of the uppermost level of the home and typically have large blades between 2-6 feet in diameter. They require attic vents to allow hot air to escape.
How Does a Whole House Fan Work?
When a whole house fan runs, it creates negative air pressure inside the home. This sucks air in through open windows and pushes hot attic air out through roof vents. The continuous influx of outside air creates a wind chill effect that makes your home’s interior feel cooler, even though the actual temperature hasn’t dropped. For a WHF to work optimally, you need to open enough windows to allow ample air to flow in.
Key Factors That Determine How Many Windows to Open
There are a few key factors to consider when determining how many windows to open with your whole house fan:
House Size
The larger your home, the more windows you’ll need to open to generate adequate air circulation. A good rule of thumb is to open at least 4-8 windows in a 2,000 sq ft home. Go higher for larger houses. You want air to flow freely through multiple rooms.
Window Size and Location
Prioritize opening larger windows on the lower floors of your home. Cooler outdoor air is denser than warm indoor air and will sink down into lower areas. Larger windows allow more airflow. You can open upper floor windows too, but focus on bigger windows downstairs.
Outdoor Temperature
You’ll get maximum cooling when the outdoor temperature is at least 10°F lower than indoors. The greater the indoor-outdoor temperature difference, the more windows you can open. When it’s hot outdoors, you may need to limit the number of windows to 4-5 to minimize heat transfer into the home.
Fan Power
Higher CFM (cubic feet per minute) whole house fans can exchange more indoor-outdoor air. A fan with a CFM between 5000-8000 requires more open windows than a 2000-4000 CFM unit. Check your fan model’s specs to determine its CFM.
Home Insulation
Well-insulated homes retain indoor air better than poorly insulated houses. You may need fewer open windows with proper insulation. Close windows once the whole house fan reduces interior temperatures to desired levels.
Recommended Number of Windows to Open
Here are some general guidelines on how many windows to open with a whole house fan based on house size:
| House Size | Number of Windows to Open |
|---|---|
| Less than 1500 sq ft | 4-6 |
| 1500 – 2500 sq ft | 6-8 |
| 2500 – 3500 sq ft | 8-10 |
| 3500+ sq ft | 10-12 |
This is just a rough estimate. Also factor in your fan’s CFM, outdoor temps, insulation, and individual window sizes when determining quantities. Start on the lower end and open more windows if airflow seems inadequate.
Tips for Opening Windows
- Open windows on at least 2 sides of your home to create cross ventilation
- Prioritize opening larger windows on lower levels
- Make sure windows can open fully to allow maximum airflow
- Open windows in multiple rooms so air circulates throughout the house
- Use box fans in windows to help pull outdoor air inside if needed
What Happens When You Open Too Many or Too Few Windows?
Too Few Open Windows
If you don’t open enough windows, your whole house fan won’t deliver optimal cooling:
- Limited airflow means hot air gets trapped inside
- Fan works harder but moves less air due to restricted intake
- Lower air exchange rate so interior takes longer to cool
- Some rooms don’t get adequate air circulation
- Higher temperature differential between indoors and outdoors
The fix is simple – gradually open more windows until you get sufficient airflow and cooling.
Too Many Open Windows
Opening too many windows can also reduce your whole house fan’s effectiveness:
- Heat and humidity from outside overload the fan’s cooling capacity
- Fan struggles to exchange air fast enough
- Airflow short-circuited from excessive intake areas
- Fan works harder but provides less net cooling
If you overdid it on the windows, start closing some beginning with upper level and smaller windows. Reduce the intake to the recommended range based on your home’s specifics.
Use Caution When Temperatures are High Outdoors
A whole house fan is less effective when it’s close to the same temperature inside and outside. The small indoor-outdoor delta means limited cooling capacity. Opening too many windows in hot weather can overload the fan and pump heat and humidity indoors. Monitor the temperature drop when you run your fan and adjust windows accordingly.
Consider Getting a Whole House Fan with a Higher CFM
If your current whole house fan is having trouble cooling your home with an appropriate number of open windows, it may be undersized. Many homeowners opt for larger 6000-8000 CFM models to maximize air exchange. This allows you to open more windows for faster cooling without overworking the fan.
Use Window Fans to Supplement Air Intake
Adding window fans in exhaust mode is a great way to increase airflow into your home. The fans will actively pull outdoor air inside, providing additional intake beyond just passive windows. Look for high-velocity window fans that can move air quickly and efficiently.
Install More Roof Vents for Air Exhaust
In addition to sufficient air intake, your whole house fan needs enough attic venting to expel hot interior air. If your fan struggles to cool your home, installing more roof vents gives the hot air more escape routes. Proper intake and exhaust are key to optimum performance.
Conclusion
Determining how many windows to open with a whole house fan depends on your home’s size, fan’s CFM rating, outdoor temperature, insulation, and more. Start by opening 4-8 windows in a typical 2000 sq ft house. From there, adjust the intake and exhaust as needed to maintain brisk, cooling airflow. Monitor your home’s temperature drop and tweak the windows until you find the sweet spot.