Can you use a box fan as a window fan?

Quick Answer

Yes, you can use a box fan as a window fan. While box fans and window fans are designed differently, a box fan can be positioned in a window frame to function similarly to a window fan and circulate air. The key differences are that window fans are built to fit snugly into window frames, while box fans are freestanding. But with some simple positioning, a box fan can work reasonably well as a DIY window fan.

Comparing Box Fans and Window Fans

Box fans and window fans serve the same general purpose of circulating and cooling air, but have some key differences:

Window Fan Design

– Specifically designed to fit in window frames
– Side brackets keep unit stable and stationary
– Extended wings on edges form tight seal with window frame
– Blades and motor positioned between window glass

Box Fan Design

– Freestanding unit, not built for window installation
– Typically larger and bulkier than window fans
– No brackets or edges to seal in window
– Exposed blades and motor

Fan Direction

– Window fans blow air directly through the window opening
– Box fans positioned to blow perpendicular to the window

Efficiency

– Window fans more efficient at circulating exterior air
– Some airflow escapes around edges of box fans

Using a Box Fan as a Window Fan

While a purpose-built window fan is ideal, a box fan can be made to work reasonably well:

Selecting a Box Fan

Look for a box fan with:

– Sturdy base to span window gap
– Front grill for safety
– Fan blades recessed in housing
– Multiple speed settings
– Size that approximates window width

Avoid box fans with:

– Lightweight bases that could fall
– Exposed blades

Measure window width and try to match a box fan as close as possible to that size. Oversized fans allow some airflow around the edges. Undersized fans won’t create a solid column of airflow through the window.

Positioning the Box Fan

The key is angling the box fan to direct airflow through the window, rather than just blowing at the window.

Place the box fan in the lower half of the window opening, tilted slightly outwards. This angles airflow upwards and out.

Brace the fan securely so it can’t shift position. Use blocks, books, or other sturdy objects to hold it in place.

If needed, use rolled towels or weatherstripping around the edges to close gaps between the fan and window edges. This helps direct more airflow through the window opening rather than escaping from the sides.

Safety Precautions

Take steps to safely secure the box fan in place including:

– Placing on a non-slip surface if using freestanding
– Securing cords safely away from window edges
– Using grounded outlet protected by a GFCI circuit
– Keeping blades guarded and hands safely away
– Checking unit stability periodically

Don’t overload outlets with more than one fan, and never leave unattended for long periods.

Pros and Cons of Using a Box Fan as a Window Fan

Pros

– Cheaper than buying a special window fan
– Makes use of existing box fan
– Can be as effective with careful positioning
– Portable and removable as needed

Cons

– Less efficient than purpose-built window fans
– Gaps around edges allow airflow leakage
– Have to improvise safe bracing solutions
– External cord is less convenient than window fans
– Harder to get full coverage across large windows

Box Fan vs. Window Fan Airflow

Here is a comparison of the airflow you can expect between using a box fan versus window fan:

Fan Type Air Circulation
Window fan 200 – 1,500 CFM*
Box fan 500 – 2,500 CFM

*CFM = cubic feet per minute of airflow

While box fans generally move more air volume (CFM), window fans are more efficient at moving air directly through the window opening because of their tight fit. A 20″ box fan and a 20″ window fan will produce different airflow through the actual window even if they have the same motor CFM.

Best Practices

To use a box fan most effectively as a window fan:

– Measure window size and get similarly sized box fan, 18 to 24 inches typical
– Angle to blow air outwards, not just perpendicular
– Brace securely in lower half of window
– Use insulation/sealant to close side gaps
– Open nearby windows for cross ventilation
– Use rear exhaust mode to pull hot air out
– Run at low speeds for white noise and air circulation
– High speeds only when occupied and awake
– Shut off and close windows completely when not home

This optimizes the cooling airflow you can achieve with an improvised box fan window setup.

Alternative Cooling Ideas

If a box fan isn’t cooling effectively enough, consider these other options:

– Buy an actual window fan that fits your frame
– Use a portable air conditioner instead, no window required
– Install a window AC unit (professional installation needed)
– Place the box fan in front of open doors to circulate between rooms
– Buy more small fans and place near occupants rather than trying to cool entire rooms
– Install ceiling fans to circulate room air and feel cooler
– Consider whole house fans for pulling in cooler night air if conditions allow

Conclusion

While a purpose-built window fan is the most efficient solution, placing a box fan in the window opening angled outwards can provide reasonably effective airflow. Securing it carefully and sealing side gaps maximizes the cooling airflow. Consider box fans a temporary fix and weigh upgrading to real window fans or ACs down the road if adequate cooling proves difficult to achieve. But never leave any fan running unattended or block airflow in a hazardous way.