We bought this for our kitchen window to bring in cooler night air and also to remove hot air from the dishwasher and cooking. The breeze around our house comes from the south, but our east-facing window doesn’t easily capture that naturally. With the Transom though, we now can get plenty of cool air in—it makes a huge difference in comfort. Getting the heat out is easy as well with a button click to reverse airflow. Regarding fit: Our window is 36 inches wide, but the opening the fan sets into is 33.5 inches, which leaves a half inch gap with the fan and blocks that fit installed. The foam blocks are sturdy and not squishy enough to mold into place to fill the gap, so we remove the fan daily to close the window and keep heat out. This is fine because it the Transom is light, but I wish there were additional block sizes available. I also wish there was a small Transom size available. We have two 21.5-inch opening double-hung bathroom windows it would be great for.