Not all models of fantastic fan have the rain sensor, the ones that do will close the vent lid and shut down the fan if rain is detected and the sensor is turned on. After awhile the vent lid will open and the fan turn on again depending on what temp or humidity is selected. If it has stopped raining then it will keep running increasing or decreasing the fan speed until the temp/humidity selection is reached. The problem I find with hoods is they become full of insects trapped in there and they are difficult to clean out..
