Just get a smart plug and connect the fan to the smart plug.
Then you can say commands like:
Turn on the attic fan.
Turn on the attic fan at 8am.
Turn off the attic fan in 2 hours.
For more customization, you can create a routine that will turn on the attic fan only during the day time, or only when the local weather report reaches 90 degrees, etc.
Most attic fans I've seen use about 200 to 400 watts. It's much more than a standard household fan, but it's no where near what a smart plug can handle. For comparison a typical hair dryer uses 1500 watts. Every smart plug I've seen can handle a max output of 15 amps, which is 1800 watts. So if your attic fan is on the high side of 300 watts, you're still way under the maximum. If you have a huge industrial attic fan that's made for a warehouse, then you're outta luck.