our old house had one, and I will probably install one here before next winter. I installed the other one, it wasn't bad. You need to be able to determine where it needs to be mounted though, as not all furnaces are installed the same (upflow/downflow, etc). Ours came off the shelf at Home Depot.
They don't affect your ductwork appreciably if installed properly. Make sure that it is wired into the relay, not on a sail switch though, ours was and it was a PITA, and sometimes didn't work if the switch got hung up.
Do NOT get a steam humidifier, those DO damage ductwork.
Oh, and you just want a bypass or wheel model, not a rotating drum. And change the filter each season, they get clogged with lime if you have hard water.
Originally Posted by KC_Connection
I am a pillowbiter.