Designed to be placed in a window, much like a window-unit air conditioner, these fans work a little differently than other types. While most fans can only cool someone directly with a stream of moving air, window fans can cool a room by bringing in cool air at night or exhausting hot air from a room. The key distinguishing feature of a window fan is whether it is manually or electrically reversible. A manually reversible fan must be removed and flipped around in the window to change the direction of airflow, while an electrically reversible fan can change directions with the flip of a switch. Some electrically reversible fans have two sets of blades that can run independently, so that stale air can be exhausted and fresh air pulled in at the same time.
One problem with window fans is that many will not fit in windows unless the screen is removed first. This means that small insects can fly in through the spaces in the fan's grille when the fan is not running. To prevent this, you may need to either cover or remove the window fan whenever it isn't in use, depending on the model.
We found the best reviews for the Lasko 2155A Window Fan (*Est. $70), which can exhaust or draw in air. It has one 16-inch fan and features a StormGuard, which allows the window to be closed without removing the fan. This was the only fan we found with a feature like this, and many users praise it. It Many reviewers also say the 2155A is exceptionally powerful -- strong enough to cool an entire house, even. However, reviews for this fan are limited. It is the highest-reviewed window fan at HomeDepot.com, but it gets fewer than 4 stars at Amazon.com. Complaints include issues with durability. While most users don't specifically mention this, at this price point, the fan does lack features like a thermostat and remote control. It does have a one-year warranty.
Holmes makes a more basic window fan, the HAWF2021 7 Twin Window Fan (*Est. $25), which has two fans and extendable panels on the sides to adjust its fit in a window. This model is manually rather than electrically reversible and has only two speeds. Amazon.com users like its low cost and ease of installation, but many find manually reversing the HAWF2021 a nuisance, and several complain that it's noisy and underpowered. We also saw several complaints about durability. This fan has a one-year limited warranty.
The Lasko 2138 8-Inch Electrically Reversible Twin Window Fan is a bestseller at Air-n-Water.com, but the fan receives only 2 stars in just three customer reviews. Users say the fan malfunctions or isn't powerful enough, though it is quiet.