The amount of firewood you need to heat a home depends on how well insulated your home is and how cold and how long your winters are where you live.
It also depends on whether you're heating only with wood or using wood heat as a supplement to your other heating source.
I heat with wood during the daytime when I'm at home and let the natural gas furnace heat overnight or when I'm away from home at work.
I heat a 1,500 square foot home that is well insulated and use 4 cords of wood per winter heating season and I get all my wood for free so only have to pay for the gasoline to cut it up and haul it.
If I heated solely with wood then I might use around 5 or 6 cords of firewood to heat with but I just let the natural gas furnace heat at night and while away so I don't have to worry about anything freezing.