I live in the northeast US and I have a forced-air furnace with central
air and an attached humidifier but the air in the house seems dry.

The humidifier pad looked dry so I poked around a bit and found the
humidistat plugged with dust and I blew it out with some compressed
air. I then saw a trickle of water over the pad but a week or so later
the air was still dry. I turned the humidistat up to 40% then 45% and
waited a day or so each time. No (noticable) change.

Aside from foggy windows and not waking up with a dry throat, how can
you tell if a humidifier is working? What else can I tweak, clean,
etc. to get it working? (Or course, we're turning the corner from
winter into spring and I won't want extra water in the air but at least
I'll know for next winter.)