After trying several plug -in room humidifiers with disappointing results, my wife and I came up with a powerless design that sets on an air duct and uses that moving air to humidify the room. We have built several prototypes and used these for 2 years now with excellent results (and no noise)!
It works like this:
Air flow from existing H.V.A.C. system duct passes thru the wick (which draws its moisture from the reservoir). As the air passes thru the wick it picks up moisture and humidifies the room.
These units could easily be vacuum formed out of plastic for a fraction of the cost of the plug in units presently sold at retailers. We feel that these units will easily sell based on the superior performance, quiet operation & powerless benefits.