Can the power fan hole be square instead of round?

It's best if the power fan airflow hole is round instead of square.

It is best if the power fan airflow hole is cut round. If the hole is cut to a 14" diagonal, the hole will be too small. It will leave the sides too short and block off some of the round opening in the fan. If the hole is cut with 14" sides, then in the corners of the square hole the round opening will be unsupported and can lead to additional vibrations since the metal can flex while the fan is running. The best case with our roof-mount fans is using a round hole, as this both ensures maximum effective use of the opening of the fan so long as it is 14" in diameter and supports the entire opening with material of the roof deck to reduce potential vibrations.