Whole-House (Central) Humidifiers are typically attached between the home's hot air ducts and cold air return, and may operate with or independently from your system’s heat cycle. The process begins where the hot air that flows into the house is diverted into the humidifier. Because this air is hot, and at a high pressure, it can hold a lot of vapor. This accumulated vapor then feeds into the cold air return where it's heated again, resulting in the water droplets vaporizing into the air. This air is then blown out through the house vents. The Primary types of Whole House Humidifiers (shown below) are Bypass, Fan-powered, and Steam
Bypass Humidifiers add moisture to the warm air from a furnace. They draw warm air from the home's heat ducts and pass it through a water panel. The air absorbs moisture which is delivered back into the air stream then into your home. Bypass humidifiers can be installed on either the Supply or Return plenum of a forced air handling system. For those who don't have a floor drain, there is a Drainless Bypass Humidifier available. These drainless styles recirculate their own water, minimizing water usage.
Fan-Powered Humidifiers work the same way as a bypass humidifier, but include a fan that blows air across the internal pad (water panel) for increased water evaporation. Power humidifiers can generally produce a gallon more of humidity each day compared to the bypass humidifier. The electricity required for the internal fan equals that of a 25-watt light bulb. Powered flow-through systems don't require a bypass duct, therefore they can be installed in smaller spaces. Power humidifiers are perfect for homes built on slabs or with HVAC systems in a closet.
Steam Humidifiers add humidity to the air by heating water electrically until it boils to create humidity in the form of steam even if the furnace isn't on. The steam is picked up by the system blower then pushed throughout the home vents. Steam humidifiers offer the fastest and most efficient method of increasing and maintaining the appropriate and comfortable level of humidity in your home. Additionally, steam humidifiers deliver a pure and best natural form of humidity that’s introduced through your entire home. Steam humidifiers will run moisture as needed, regardless your current heating or air conditioning situation.