Furnace Humidifiers

The most convenient type of humidifier is a furnace humidifier (sometimes called a bypass humidifier).  They are built right into the central furnace or air conditioning system.  Therefore, they don't need to be manually filled with water, though they still need occasional maintenance.  Furnace humidifiers are considered a good way to save money on heating, while also raising the humidity to comfortable levels.

Furnace humidifiers come in a few different styles.  The most basic type is the drum style, and works very simply.  A pipe pumps a steady supply of water in a reservoir, and a foam pad absorbs some of the water.  Then, hot air is forced through the pad, which also takes some of the moisture with it, thus increasing the humidity in the entire house.  These furnace humidifiers are very cheap, though they have to be closely monitored for mold.  The pads need to be changed often, but they are not expensive.

A second variety of furnace humidifier is the disc wheel style.  Like the drum style, this one uses a reservoir, but instead of a foam pad, water is trapped in a filter-like object comprised of many small plastic discs.  The best thing about these humidifiers is that they don't need much maintenance or replacement of parts.  However, they are more expensive to operate.

The third and final style of furnace humidifier is the flow-through variety.  This type uses a filter that resembles a honeycomb, though it's actually made of a ceramic material (one is pictured below).  There is no reservoir in this type of humidifier; instead, when the hydrostat (the humidity monitor) indicates dryness, water is automatically sprayed onto the pad, and then hot air passes through.  This type of humidifier is efficient, and the maintenance is minimal, with the pad needing to be replaced only about once per year.  On the downside, the initial price is usually higher.

If you use a furnace humidifier of any variety, be sure to turn it off when the air conditioner is running (if it's not automatic), because part of the purpose of an air conditioner is to decrease excess humidity.  And when running a furnace humidifier, be careful not to set the humidity to high, because this can cause mold and other problems throughout the house.