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The drum and sponge humidifiers (also known as the evaporative wick design) were designed for forced-air systems. The basic idea of this type of humidifier is that the sponge rotates on the wheel of the unit. As it rotates, it dips into a tray of water, and the moisture from the wet sponge is then distributed through the house when the forced-air furnace runs. The problem is that the moisture is not adequate to add enough humidity to the home. Also, depending upon the hardness of your water, the sponge can become caked with sediment and will need to cleaned or replaced often. Another negative aspect of this type of furnace humidifier is that the stagnant water in the tray can become a health hazard due to mold and bacteria.
Flow-through humidifiers, although an improvement upon the drum and sponge units, still require quite a bit of maintenance and also are expensive to operate. With a flow-through unit, a steady stream of water drips on to a metal or plastic screen. As air blows through the screen, the moisture is spread throughout the home via the heating ducts or system. Excess water is disposed of through a floor drain. The negative aspects of this type of furnace humidifier are wasting water (a valuable and expensive resource), and excess water that is put into the system puts yet another demand on our water infrastructure. - The rotary-disc humidifier operates by a wheel assembly, which is made up of textured plastic discs. These plastic discs rotate through a tray of water and operate like the drum and sponge units but without some of the problems. The unit requires a yearly cleaning, but there are no sponges to clean or replace. And, it has automatic flushing, which you can program to flush the tray of water.
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One important feature to look for in your built-in furnace humidifier is a humidistat. A humidistat determines the amount of humidity in your home. You are able to set the humidistat to your desired humidity level.
Select a unit that is hooked up to your water supply and that will automatically fill the water reservoir in the humidifier. Otherwise, you will have to do this manually, which means that you will have to remember to check and fill the reservoir of your unit.
