During the winter months, as outside temperatures drop, so does the relative humidity (rh) inside a home. This “thirsty air” begins to absorb moisture from everything it touches, such as woodwork, furniture, paintings, wooden musical instruments, carpet, wood molding, kitchen cabinets, doors, and floors. Moisture is then pulled and absorbed from these hygroscopic, or moisture-retaining, materials, and damage can occur.

For example, cracks will appear in wood floors, leaving a dull finish. Furniture may warp and become loose at the joints. Rare paintings can be destroyed in only a few years as paint cracks and flakes from the canvas. Carpets can deteriorate quickly, and doors will seem to warp before the homeowner’s eyes. Contractors need to keep in mind the symptoms and dangers of poorly controlled humidity levels of indoor air for homes during the winter months.


Here are 10 basic things contractors need to know about humidification:

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To foster healthy indoor living, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends keeping indoor humidity levels between 40 and 60 percent rh. Relative humidity is the ratio of the amount of water vapor in the air at a specific temperature to the maximum amount that the air can hold at that temperature, expressed as a percentage.

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Humidity levels that are too low can aggravate symptoms of asthma, rhinitis, and respiratory infections.

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Proper humidity control can improve the health and comfort of people living in the home.

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Proper humidity levels decrease static electricity in the home, eliminating static shock and protecting valuable electronics.

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Bacteria, viruses, mites, and fungi are virtually inhabitable when a home maintains healthy indoor rh.

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Mold growth indoors is a serious issue for homes today. Molds are incapable of obtaining moisture directly from the air. Molds thrive indoors when the rh range is consistently from 60 to 99 percent at surface substrates.

This is why properly insulated walls and surfaces of a home are crucial to preventing high temperature differentials between the ambient air and an outer wall. The temperature of a surface at or below its dew point can cause water condensation on a given surface, allowing germination and mold growth regardless of ambient humidity.

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Proper humidity control can be significant to reducing energy consumption.

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Proper humidification will make one feel warmer and more comfortable.

A properly controlled whole-house humidifier is designed to decrease the rate of evaporation of moisture from the human body, leaving one feeling warmer at lower temperature settings, thus saving energy costs.

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Humidity levels that are too low will cause the air to become “thirsty.” This extremely dry air can warp furniture and door frames. Woodwork, paintings, and other valuables can be vulnerable to a low indoor moisture level as well, sometimes causing irreparable damage.

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Carpeting can also deteriorate quickly in a low-humidity home.


By stabilizing the humidity level indoors, hygroscopic materials - woodwork, furniture, and paintings, for example - will not absorb or give off moisture, protecting them and other valuables from irreparable damage.

When faced with a low-humidity situation, contractors need to understand the cause and possible solutions. One such solution is whole-house humidifiers, which connect directly to a furnace and work with the heating system to distribute moisture throughout the home. These humidifier types rely on furnace heating cycle temperatures to deliver the rated humidity capacity output.

An effective whole-house humidifier injects steam into the airstream with a specifically designed nozzle that allows the vapor gas to be efficiently absorbed at temperature as low as 70°. This type of humidifier is not dependent on the heating cycle to deliver humidity capacity, but only needs airflow as low as 800 cfm at 70°.

Both contractors and homeowners often misunderstand steam humidifiers. The common misperception is that steam humidifiers put water droplets into the air distribution system and cause unwanted pools of stagnant water and damage. This is not true.

Actually, steam humidifiers that use electrode technology to boil water in a renewable steam-generating cylinder are designed to inject pure, sterile steam vapor into the duct airstream, where it is designed to be completely absorbed quickly and efficiently. Meanwhile, electrode steam humidifiers are designed to deliver greater capacity outputs on demand to meet challenging humidity loads to maintain designed rh set points.

Controlling humidity can be a challenge for today’s heating contractor, especially during the winter months. By understanding humidity symptoms, problems, and possible solutions, contractors can better meet the needs of their homeowner customers.

Publication Date:10/15/2007