If you have never been able to entice brown-headed nuthatches to nest in your nesting boxes, adding 1-3 inches of dry nesting material such as pine shavings, sawdust or wood chips to a nest box just might change your luck.
I should note the only times brown-headed nuthatches have nested in my boxes is when I added nesting material.
Who knows? This simple technique might just work for you.
When we lived in Macon I usually had them using crape myrtle bark, making a shallow nest. After they left, chickadees would nest. Here in Dalton I have not seen any. Just white breasted nuthatches.