Furnace Humidifiers: For the Home

Bypass, Steam, Spray Mist and Desert Spring

Furnace humidifiers

Furnace humidifiers are basically whole house humidifiers that are used with a central heating system during winter when the air in your home can literally become as dry as the desert.

Most furnace humidifiers use the ductwork in a heating system to move the air through the humidifier and to circulate it throughout the home.

The three main types of home furnace humidifiers are as follows:

Bypass humidifiers

Bypass humidifiers are the most commonly used home humidifiers on the market because they combine affordability with effective operation. They are normally mounted in the supply duct of the heating system where forced air is pushed through the humidifier and on into the house. This method ensures that the humidifier uses as little electrical power as possible making it an economical choice.

Bypass systems make use of warm forced air from fuel burning furnaces to humidify the air. A foam drum or vertical pad is soaked in water from a reservoir so that when warm air is passed over it, the water evaporates thereby producing humidity. Electric furnaces and heat pumps don’t produce air warm enough to cause the water to evaporate effectively and so these types of heating systems would require a steam humidifier.

Steam humidifiers

In contrast to bypass systems, steam humidifiers are very expensive and are only really used in large buildings. They work in a similar way using forced air from the furnace to circulate humidified air throughout the building. The main difference is that an electrically heated element, instead of warm air, is used in the water reservoir to evaporate water.

Spray mist humidifiers

Spray humidifiers do exactly what the name suggests; they spray fine droplets of water into the air which is then carried through the ductwork of the furnace heating system into the home. There are two ways of doing this: using a nozzle to spray out water droplets or ultrasonic technology. These methods are covered in more detail in the ultrasonic and warm mist humidifier pages.

Spray mist systems are generally the cheapest and easiest to install but they are not as effective as the above mentioned furnace humidifiers and so they are not recommended for use in very dry conditions. They also require more maintenance as minerals from the water tend to collect in the ducts and cause ‘white dust’ to form on surfaces in the home.

Desert Spring furnace humidifiers:

Don’t use metal screens or foam pads for water evaporation – minerals stick to these and the build-up decreases the surface area for water to evaporate from and restricts air flow.

Desert Spring’s unique design uses a number of plastic discs stacked together to form a grooved drum. Water adheres to the grooves and evaporates when warm furnace air flows over it, leaving minerals behind inside the grooves. The mineral residue is washed off in the water reservoir with each rotation thereby reducing the amount of mineral dust in the home.

These grooves also increases the evaporative surface area, reduce amount of maintenance and reduce the growth of bacteria and mold in the unit.


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