Drier vs. dryer

Drier is a comparative adjective meaning more dry. The word is never used to denote an electrical appliance. This is incorrect:

As Sherrod sat under the hair drier, a customer came and hugged her and asked for an autograph. [Atlanta Journal-Constitution].

And this is correct:

Readings in the upper 80s to near 90 this afternoon are combining with drier air to make it a rather pleasant day out there . . . [Washington Post Capital Weather Gang]

A dryer is an electrical appliance used to dry hair, clothes, or anything else. This is incorrect:

Gusts of hot, humid air mix with cooler, dryer air at every step of the process. [Ottawa Citizen]

And this is correct:

The sleek Xlerator hand dryers may blast the water away, but their decibel level can spike into the mid-90s . . . [Chicago Tribune]