Differential temperature control

I’m trying to find a differential temperature controller. I’m sure that what I need exists, I’ve just been unable to stumble on the correct search terms and was hoping for some help here. I’m looking to be able to turn on a ventilation fan when it is cooler outside than it is inside for my shop. So it would need 2 temp probes; P1 for inside temp and P2 for outside temp. When P1 > P2 it turns fan on. When P1 < P2 it turns fan off. Can someone help me find what I’m looking for?

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