It's my understanding that some electrical devices (like TV's?) are very sensitive about the volts and amps they are fed. However, others (such as filament light bulbs) are very tolerant of varying current.
Wind is highly variable, and very often too low to be very useful. By storing what wind you do have over 24 hours in a battery, you can then get a steady flow for a short while to perform some kind of work. As a result, there is a lot of experience here about making a wind-gen to charge a 12/24/48-volt battery pack.
Its possible to build a generator that never alternates the electron flow direction, but if you do alternate the direction of the pulses, you will get a higher output from the same size of generator. Rectifiers can convert the alternating current into DC.
I've been given the impression that DC motors are easier and cheaper to run off of variable current.
A magnet has an invisible magnetic field of a certain size (flux). You can fill that space with copper wire to form a coil, but any extra copper wire outside the flux will add length and resistance without adding any work. Since the flux size is set, you can use a few turns of thick wire (low volts/high amps) or many turns of thin wire (higher volts/lower amps) to fill the space.
I've been reading about adding an electric motor to a bicycle. Motors are "wound" for a specific voltage, amperage, and RPM. Its better to over-volt a motor than undervolt one. By that I mean if you put 48 VDC into a 36 VDC motor (industrial floor scrubber), you'll get more power and a little more heat. However if you put 48 VDC into a 90 VDC motor (free trash treadmill) the 1/2 volts will only give you 1/4 the power (I don't know why, but I've been assured that its true).
I point this out because if you build a wind-PMA for 120 VAC (It can be calculated, but there aren't any examples I know of to follow) and its barely turning, you probably wont get any useable amps of current to spin a 120 VAC fan, especially with transit losses. And if you use a low volt fan so it will work during low winds, a high wind will overheat the fan motor.
If you are certain you want a direct feed windgen-to-fan, my best guess (and I'm not experienced with windgens) would be to use a well-established 24-volt windgen design to feed a 12-volt car radiator fan adapted to your attic vent. In the winter you can switch the feed to heating water. Read the "heat" section, and search "water dump load 24-volt".
Later, you can add two 12-volt batteries in series for a 24-volt storage with a charge controller and an inverter, so you can run some lights and TV for a short while when the power is out. Best of luck, and have fun.