[undy]

I would imagine your fan will draw around 20 to 25 amps. Automotive relay manufacturers tend to rate their relays on the ragged edge of failure. The extra amp capacity of the 70 amp relay will give you some appreciated increased relay longevity. I'm running the Bosch 70 amp on my 2800 cfm flexalite. The x-tra capacity gives me a zero volt drop across the relay's contacts.

Dave