We have two Carrier two-stage forced air furnaces. Each has an Aprilaire 560 flow through humidifier mounted right above the blower. They turn on when the furnace fires. Water flows through the media and shuts off when the blower stops. The media dries out between firings -- no mold forms. Excess water runs through a tube into basement floor drains.

This system requires a water feed line and controls that mesh with the furnace ignition, as well as a control for the amount of humidity you require. There is also a baffle on the duct connecting the humidifier to the furnace ducting. The baffle stays open in winter is closed in summer. As 'overkill', I turn off the water lines and set the humidistats to nil.

We've had no problems for 18 years. (Replacing media from time to time.)

I have tried the two different units (one steam and the other an Aprilaire pass through) with no success whatsoever. Another company is trying to talk me into the Aprilaire 800, a steam unit, but "been there, done that". I do not understand hwy I am having such a problem getting any humidity at all. The thermostats in the house never manage to go bellow 21 or 22% and the paint actually cracks in some places because it is so dry.

Are you *heating* your home now? (We are still using our air conditioning here, near Chicago.) I'm not aware of how a humidifier works with A/C.

No, not using heat now. Using AC and humidifier is not operational. However, heating season will be here soon and I need a solution.