Editing Humidifier (section)

=== Bypass flow-through ===
Bypass flow-through style (bypass – also known as "biscuit style" or many other, similar variant names) uses a pipe to bring water directly to an electrically controlled valve at the top of the humidifier. Air passes through an aluminum "biscuit" (often called a pad; the term "biscuit" emphasizes the solid rather than foamy form) which is similar to a piece of extremely coarse [[steel wool]]. The "biscuit" has a coating of a [[Gloss (material appearance)|matte]] ceramic, resulting in an extremely large surface area within a small space. When the hygrostat calls for humidity, the valve is opened and causes a spray of water onto the "biscuit". Hot air is passed through the "biscuit", causing the water to evaporate from the pad and be carried into the building.
:Advantages include:
:* Reduced maintenance (new "biscuit" is needed only when clogged with dust or mineral deposits, typically once per year)
:* Lack of a pan of potentially stagnant water to serve as a breeding ground for mold as with a drum-style humidifier
:* No incidental humidification caused by a constantly replenished pan of water in a high velocity air stream
:* Reduced requirement for expensive air filters
:* Uses little electricity
:Disadvantages include:
:* A somewhat higher purchase price
:* Manufacturer and model-specific replacement biscuits (versus the relatively generic drum-style pads) may be more expensive and difficult to find
:* For most models, a portion of the water supplied to the unit is not evaporated.  This can generate a considerable amount of waste water containing residual minerals, which does require connection to a drain. There is a limited selection of drain-less models that recirculate water, but mineral buildup must then be removed manually on a periodic basis.