No offense meant by the title! It just seems more and more people are worried these days about controlling the level of humidity in their homes. That makes sense, because the level of relative humidity can have a huge impact on both people and inanimate objects inside. Relative humidity (RH) is computed by dividing the amount of moisture in the air by the amount it can hold without dropping it in the form of precipitation. The moisture content of air is affected by activities and conditions within a home, as well as the weather outside it. The amount of moisture the air can hold is affected by temperature.
A more useful way of looking at relative humidity is to see it as a measure of the air’s tendency to absorb or release moisture to objects or people nearby. When the RH is high, moisture tends to transfer to other absorbent materials. When RH is low, moisture moves back into the air. Indoor humidity changes in large ways with the passage of the seasons, and in smaller ways depending on what’s going on in the room. For example, the breath of only one person disperses a quarter-cup of water per hour. Cooking for a family of four produces five pints of water vapor a day. Showering releases half a pint. As RH is affected by numerous variables, controlling the temperature alone won’t regulate it. Only four to six pints of water released into the air raises the RH in a thousand-square-foot home anywhere from fifteen to sixty percent.
So What?
If the air outside is a wintry 0° Fahrenheit and the relative humidity is 75%, but the air inside a home has been heated to 70°, then that air will have an RH of only 4%. That doesn’t sound too bad, does it? No, it probably doesn’t, until we realize the average RH in the Sahara Desert is 25%. The human body is far more comfortable when humidity levels are between 20 and 60%. If the temperature outside is above freezing, an RH of 35 to 40% is even better. That changes as the temperature decreases. If it’s colder than 20° Fahrenheit outside, an RH higher than 30% can cause excess condensation on windows and the insides of exterior walls. This can lead to serious structural problems over the years.
It may seem strange, but effective insulation and tight construction can actually worsen humidity problems unless the home is properly maintained. That’s because tight-fitting doors and windows act as “vapor barriers” that can trap heat and moisture inside. Proper ventilation is required to draw water vapor away from walls and ceilings, where it can cause wet insulation, loose paint, and mold that can seriously harm the house’s occupants. High RH causes a musty odor and clammy feeling in the air. It’s also extremely uncomfortable.
Low humidity is just as damaging, especially to people. At low levels, the body loses moisture so quickly that it feels chilled, even in comfortably warm areas. The mucous membranes in the nose and throat dry out, which is not only uncomfortable but also destroys the intended function of those membranes—namely, to ease respiratory problems and ward off the common cold. Dry air creates static electricity. It desiccates skin and hair, causing itching and chapping.
The Piano Technician’s Guild warns that fluctuations in relative humidity can be damaging to pianos. As the wood in a piano absorbs and then releases water, the wood swells and shrinks. This is especially true in the piano’s soundboard. The soundboard is a sheet of wood about three-eighths of an inch thick. Piano strings pass over the soundboard and are connected to it by a wooden piece called a bridge. As the wood of the soundboard expands, the bridge is pushed harder against the strings, which draws them out of pitch.
Because the soundboard is slightly curved, the pitch rises higher in the middle octaves than at either side. This effect is not entirely corrected when the soundboard shrinks again. Humidity control allows for more constant tunings at the standard pitch level (i.e., the level at which A represents 440 cycles per second). Humidity control also protects the piano’s wood, finish, metal parts, and glue joints.
The warning signs of unhealthy humidity levels include heavy condensation of frost on windows, mold, mildew, musty odors, frequent chest or head colds, or nasal stuffiness. To gauge indoor humidity, drop three ice cubes into a glass. Add water and stir. If moisture doesn’t condense on the outside of the glass in the next three minutes, then the air is too dry. (This test shouldn’t be performed in a kitchen, where cooking vapors can throw off the results.) High humidity will be more obvious, as it causes sweating and the familiar summertime “sticky” feeling. Excess mold on closet walls or room walls and ceilings is a clear giveaway.
So Fix It!
The most obvious way to control humidity in the home is to buy machines that do exactly that, and we’ll get to those in a moment. But perhaps such drastic measures are unnecessary. The Minnesota Blue Flame Gas Association recommends the following simple steps to help regulate indoor humidity.
• Take shorter showers in cooler water.
• When cooking, cover pans and use range exhaust fans.
• Use the bathroom exhaust fan after showering or bathing.
• Reduce the number of plants in the home, or water them less.
• Vent clothes dryers to the outside.
If those ideas don’t do the job, then mechanical methods will be required. There are three standard types of humidifier that raise room RH levels. Evaporating humidifiers contain pans or absorbent plates full of water, plus radiators or warm air heating units to create water vapor. Portable humidifiers are basically smaller versions of evaporating humidifiers that push air through a wet pad. (The water in portable devices must be replaced regularly.) Power humidifiers are more complex. They draw water from the house system and push it through the furnace air stream, as directed by a humidity control device called a humidistat. The humidistat is located near the furnace thermostat, and the humidifier itself is often built directly into the forced air heating and cooling system. Newer model whole-house dehumidifiers, powered by natural gas, can remove up to eight pints of water a day. They use a dry, absorbent material called a desiccant to pull moisture from the air.
In colder climates, an air-to-air heat exchanger may be a wise purchase. These devices take heat from outgoing air and transfer it to the fresh air they allow inside. Up to eighty percent of the heat that would normally be lost is returned to the home. They can be installed as part of the central heat and air system, or in windows or walls in the manner of a window air conditioning unit.
The Allergy Buyers Club rated over a dozen room humidifiers, including several of the most popular models. Four of these products earned their highest rating of five stars out of five. The top two were made by Slant Fin. The cheaper of the Slant Fin models was the Germ Free 300-Watt (GF-300), a 2.75 gallon warm mist humidifier. It uses a stainless steel reservoir with a mineral pad to absorb dust and other contaminants. It also uses ultraviolet light to kill any bacteria that may accrue in the standing water reservoir. The product costs $129.99 and is available from Amazon.com or directly from SlantFin.com. Only slightly more expensive was the Slant Fin GF-350, which holds 3.5 gallons and includes the same features as the GF-300. The GF-350 does make an occasional gurgling sound, but is otherwise silent and earned top reliability ratings. The reservoir lasts for forty-eight hours without refill, and the device raises humidity over four hundred square feet of space. The GF-350 is also available from Amazon and SlantFin.com. Its ultraviolet light unit should be changed every year or two to ensure continuous destruction of dangerous bacteria, mold, and spores.
The other two five-star humidifiers were both made by Hunter, the Care-Free Humidifier Plus with Digital Humidistat and the same model with a Nite-Glo option designed for children’s rooms. These two models cost anywhere from $74.95 to $94.95. They don’t include a UV device to kill bacteria, but they do contain a patented Permawick antimicrobial fiber that requires cleaning only once a season. Hunter humidifiers are sold online at HunterFan.com/humidifiers, and they’re also available in Amazon.com’s Home and Garden section.
Recent Comments