Several temperature classes exist for axial fans
Standard temperature fans are those operating at a maximum of 55 °C.
F300 / x h fans can operate at 300°C for a specified number of hours. So F300 / 2 h can withstand the stresses of 300°C for 2 hours before it fails. These fans are used for smoke extraction in case of fires
Similarly F400 / x h fans operate at 400°C for a specified number of hours. Again these are primarily used for smoke extraction purposes and fail after the specified time.
Other similar smoke extraction temperature classes exists such as F200 or F250.
In many parts of Europe, all smoke extraction fans have to be tested and certified by a regulatory body. The tests are done to see if the fans, specifically the motors, can withstand those high temperatures for the specified time. Failing to do so means no certificate and thus no sales in those countries requiring certification.
There also F600 fans able to withstand 600°C for a specified time. To my knowledge there are no motors able to withstand these temperatures. These fans place the motor away from the hot air stream in an insulated motor bay. This way a F250 or F300 motor can be used to withstand 600°C for two hours.
Fans designed to face high temperature continuously (and not just for 2 hours) use the same principle, by placing the motor away from the airstream.
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