Noise cancellation is a mixed bag, if the fan hum is in the Hz of your grandfather's speech, then it will effect his
speech too. I've had better luck with minor filtering followed by adjusting the audio gain of the recording. Fan noise is typically sub-consciously auto-canceled by the hearer anyway. It's probably why it's in the recording in the first place, the people doing the recording didn't even know it was there until after the fact.
I send you a boardmail.