How deep into the earth do you need to drill before you reach heat in excess of 100deg fahrenheit?

Answer 1

This will depend on location. Temperatures are hotter in California (where we drilled north of Ventura) and in other areas of the country. They will throw the above equation out of balance.

Answer 2

From the surface down through the crust the normal temperature gradient (the increase of temperature with the increase of depth) in the Earth’s crust is 17 - 30°C per kilometer of depth (50-87°F per mile). So if the surface is at 50°F, then you'd need to only go down a mile.