anemic rear defroster and side mirrors? >>>

it's been in the upper 30s the last few mornings with lotsa dew and whatnot - chilly indeed, but no ice. i fire the rear defroster up and after a 10 minute drive, the rear window is still covered with dew...and only a hint of clearing.

my side-mirror defoggers are similarly anemic. they work, but slowly.

any suggestions to remedy or debug this?

walter