UL has reviewed the Corso Box fans and found them to be safe from overheating. The fan I bought at Home depot also had a thermal protection switch Underwriter's Lab approval of DIY Box Fans "Across all fan/filter test scenarios, the most notable temperature increases were observed at the motor and motor windings. However, all measured temperatures fell below the maximum acceptable thresholds defined by the market safety standard for electric fans (UL 507). Exterior surfaces that can come into direct contact with people remained below 36 °C, which is below the first-degree burn potential of 47.5 °C. Further, an extreme scenario where both the front and back of the fan were blocked for an extended period of 7 hours did not pose any observable fire hazards. And after an initial rise, temperature remained steady throughout the test."