I have an old, dead, Aprilaire 110 (or 100) that never worked since I
bought my house. I'd like to replace it with a working humidifier.
Any suggestions on what a good replacement model would be? The house
is about 2,500 sq ft. I'm hoping I can find something that will fit
the hole and connections I already have.

I understand that replacing a humidifier isn't rocket science. Too
bad. I'm pretty good at rocket science. HVAC on the other hand...