they make two diff models
one option to attach onto the a/c ducting and controlled by such. and then 2nd option it is for non ducting/a/c and basically you will need good quality water without lots of trace /contaminate .
non a/c version, this is what I was going to get but I went diy ( kinda wish I went this route cause I have little to more room for a tout on the ground )
The Aprilaire Model 801 is a modulating steam humidifier that evenly distributes 34.6 gallons of moisture to spaces up to 6,200 square feet.
www.sylvane.com