Curious Electrical Issue

I just received my new bathroom vent fan!  I cut open the box and studiously read the manual.  The directions said that I needed a "dedicated 20 amp breaker".  I have no idea what breaker is assigned to the bathroom.  Ok, a trip down into the basement is needed.  I open the electrical box and behold:

No lables?!  That just makes things a bit complicated. My wife and I spend the next hour going over switch by switch.  I delegated her to turn on all the lights and carry around an old plug in alarm clock for the rooms that have no hard wired lighting.  We each had an iPhone that we used in Facetime mode.  As I flipped each breaker to off, she would go room to room to find what was still on and what was out.  This method solved several of the unknown labels (especially when I kept accidentally turning off Breaker No. 4, turning off our WIFI, no WIFI = no Facetime) but a few of the breakers are still unknown.  And more alarming is that with all the breakers off, half of the lights in the kitchen were still on.

Here is what was figured out:

Breaker

1.  20 Amps - Unknown.
2.  15 Amps - Unknown.
3.  20 Amps - Unknown.
4.  15 Amps - Second Floor: South Two 
              Bedrooms.
5.  20 Amps - First Floor, Library.
6.  15 Amps - Oil Furnace.
7.  15 Amps - First Floor: Rear Stairs, 
              Dining Room, Living Room.
8.  15 Amps - First Floor: Half Bath, 
              Kitchen Addition, Porch; 
              Basement: Lights.
9.  15 Amps - Second Floor:  Full Bath.
10. 20 Amps - First Floor:  Kitchen Light 
              Over Sink & Dishwasher?
11. 15 Amps - Unknown.
12. 20 Amps - Unknown.
13/15.  80 Amps - Cloths Dryer.
17/19.  60 Amps - Oven and Range.
14. 20 Amps - Microwave.
16. 20 Amps - Radon Pump.
18. 15 Amps - Attic.
20. 15 Amps - Master Bedroom.
21. 15 Amps - Unknown.
22. 20 Amps - Main Entry Lighting and 
              Exterior Front Lights.
23. 15 Amps - Basement: Electrical 
              Socket (Dehumidifier).

I guess I have to figure out a solution for the bathroom vent.  I wonder if I can use one of the "Unknown" 20 Amp breakers?  Since they do not control anything (assuming that is) then perhaps I can just feed a wire down from the attic and plug it into the breaker box.  I'll have to look into that.