Humidity is simply vaporized water in the airYour breath contains hundreds of droplets of invisible water vapor. You can see them when you breathe on a pair of cold glasses. The term most often used to define the amount of water vapor in the air is "relative humidity." Relative humidity is the percentage of water vapor in the air at a specific temperature, compared to the amount of water vapor the air is capable of holding at that temperature.
Warm air holds more water vapor than cold air. When air at a certain temperature contains all the water vapor it can hold at that temperature, its relative humidity is 100 percent. If it contains only half the water vapor it is capable of holding at that temperature, the relative humidity is 50 percent. If the outside air temperature in winter is 0°F and the relative humidity is 75 percent, that same air inside your 70°F home will have a four percent relative humidity. That’s dry!
When air is saturated with water vapor, it has reached the dew point; at this point, water vapor condenses and produces visible water or "condensation." In winter it usually occurs first on windows. When warm, moist air comes in contact with a cold window, air temperature drops and it can no longer hold the water vapor; condensation results.
Desirable Humidity Levels
The human body is comfortable when relative humidity ranges between 20 and 60 percent. In your home, average relative humidity of 30 to 65 percent is appropriate when outside temperature is 20°F or above. However, during cold weather, higher humidity ranges may cause structural damage because of condensation on windows and on the inside of exterior walls. As outdoor temperatures fall, condensation problems inside may develop. The construction of a home also influences how much humidity is desirable. Tightly constructed buildings with properly installed vapor barriers and tight fitting doors and windows retain more heat and moisture. This is where mechanical ventilation becomes important. If a home does not have the proper mechanical ventilation, excess water vapor can move through walls and ceilings, causing wet insulation, peeling paint, and mold on walls and woodwork.
How to Gauge Indoor Humidity
Drop three ice cubes into a glass, add water and stir. Wait three minutes. If moisture does not form on the outside of the glass, the air is too dry; you may need a humidifier. (Do not perform this test in the kitchen, because cooking vapors may produce inaccurate results.)
Frequent fogging of windows may indicate too much humidity. The appropriate relative humidity will allow only slight condensation along the lower edges or corners of windows. More condensation could be damaging.
Moisture buildup or mold on closet walls or room ceilings and walls indicates high humidity.
If Humidity is Too Low
Low humidity causes static electricity, dry skin and hair, and itching and chapping. Mucous membranes in the nose and throat dry out, increasing your discomfort and susceptibility to colds and respiratory illness. With low humidity levels, body moisture evaporates so quickly that you feel chilled even at higher thermostat settings.
Adding a humidifier to your home will remedy these problems. There are three standard types of humidifiers from which to choose:
Evaporating: With this type of humidifier, moisture evaporates into the air from a pan or absorbent plates partially immersed in water and attached to the sides of a radiator or a warm air heating system; limited humidification capacities.
Portable or Room: In a portable or room humidifier, air circulates through a wet pad or a very fine mist of water is discharged into the room. The unit may be moved from room to room as desired, though water must be manually added.
Power: In a power humidifier, moisture is introduced directly into the air stream circulating through the furnace; water is fed automatically into the unit by a connection to the house water system. A humidistat (humidity control) should be located near the furnace thermostat or in the return side of the duct system. The unit may be built in or attached to a forced air heating system.
Important Notes About Portable Humidifiers:
Many families use portable cool-mist humidifiers to increase moisture levels in the air inside their homes. When used as directed by the manufacturer, portable cool-mist humidifiers are a safe product. However, using one without properly cleaning and disinfecting could contribute to additional breathing problems for people who have asthma, severe allergies and other respiratory difficulties.
There are three types of portable humidifiers. Vaporizers contain a heating element that boils water and puts moisture into the air by sending out a stream of hot mist. Ultrasonic humidifiers produce a micro-fine mist when water is passed over an ultrasonic nebuliser (high frequency vibrating apparatus). Cool-mist humidifiers work without heating the water. A motor forces the water droplets into a mist which is then dispersed into the air.
Portable humidifiers are not likely to cause health problems if manufacturer directions are followed. Directions usually include emptying left-over water after each use, as well as cleaning and disinfecting the water reservoir on a regular basis. However, of the three types of portable humidifiers, the cool-mist humidifier may contribute to health effects if water is left sitting from one use to the next because:
• Bacteria can collect and multiply in sitting water;
• A cool-mist humidifier does not boil the water, so it does not kill the bacteria;
• Re-starting a cool-mist humidifier could send spores of bacteria into the air in your home The bacteria spores could then make matters worse for people who already have difficulty with their breathing.
Many consumers have concerns after using cool-mist humidifiers because they notice tiny, dust-like particles on nearby furniture. Some models may release high concentrations of particles into the air when they are filled with tap water. These particles are made of the same materials that cause the build-up of scale inside kettles and are considered harmless to most people. However, if the tap water used in the cool-mist humidifier contains toxic substances, there is a risk that the particles could be harmful. The number of particles released into the air is generally much lower when distilled water is used.
Using Your Cool-Mist Humidifier Safely
To safeguard your health when using a cool-mist humidifier, you should:
• Clean and disinfect the water reservoir of your humidifier on a regular basis according to the manufacturer's directions. Instructions may vary depending on the type of
humidifier and frequency of use.
• Never leave water sitting in a cool-mist humidifier when you are not using it.
• Always empty the water reservoir when you turn off the humidifier.
• Clean and refill only when it is to be used. In most cases tap water is fine, as long as you change the water and clean your humidifier on a regular basis.
• Keep the humidifier in a central location and out of your bedroom, especially at night.
Power Humidifier Notes:
Types of Power Humidifiers for use with central, forced air heating systems :
• Flow-thru humidifiers
• By-pass humidifiers
• Steam humidifiers
The bypass humidifier is the most common furnace humidifier. Flow-thru humidifiers work through evaporation, only putting as much moisture into the air as the air can handle, which varies depending on the room temperature. Steam humidifiers add moisture to the air no matter the air's temperature.
For areas with low humidity and cold weather, the steam humidifier is the best choice available today. The key features of the steam type humidifiers that make them so attractive are:
• The water in the system is flushed and replaced every 24 hours. Flushing helps to ensure that bacteria and mold cannot build up in the humidifier Humidity can be put into the home without the furnace in a heat-cycle, so that as long as the fan is running, humidity is being added to the air.
• No homeowner maintenance is required, no filters to clean or replace
If Humidity Is Too High
High humidity levels produce constantly fogged windows, musty odor and/or a clammy feel to the air. During cold weather, condensation in the lower corners and edges on prime (inside) windows is common. Excessive condensation on prime windows indicates loose storm windows; seal storm windows by caulking and weatherstripping. Condensation on the inside surface of storm windows indicates loose prime windows; seal prime windows, also by caulking and weatherstripping.
If you maintain high humidity, expect to have more window condensation. Remember that structural damage may result from extended periods of high humidity. Excessive humidity can be temporary. During summer, outdoor humidity is high; your house and its furnishings naturally absorb some water vapor. In the fall, when temperatures drop and the air becomes drier, water vapor is released into the living space and temporary condensation on windows may occur.
If your home has high humidity you may want to consider a dehumidifier. These units are either portable units for smaller spaces or a whole-house dehumidifier that is attached to your forced air heating and cooling system.
Dehumidifier Basics
Capacity: Dehumidifier capacity is usually measured in pints per 24 hours and is determined by two factors: the size of the space that needs to be dehumidified and the conditions that exist in the space before dehumidification. For example, a 2000 square foot home with moderately damp levels of humidity would need a dehumidifier with a capacity of 22 pints per 24 hours. The same house with extremely wet conditions would need a unit rated at 37 pints per 24 hours.
Water Removal Options: Most portable dehumidifiers use a removable plastic bucket and warning lights to indicate when the bucket is full and needs to be emptied. Typically the unit will automatically shut off when the bucket is full, so you don’t have to worry about the bucket overflowing. Most portable dehumidifiers and all whole-house dehumidifiers come with a fitting that allows you to hook a hose directly to the bucket, which can then be directed into a floor drain or sump pump, so there is no need to empty it.
Placement: Most portable dehumidifiers have a top-mounted air discharge and can be placed against a wall; if the unit does not have a top-mounted discharge, make sure the dehumidifier is located away from walls and furniture, so that air can circulate freely around the unit. Doors and windows to the space being dehumidified should be closed while the unit is running to ensure that the space is dehumidified as efficiently as possible. Locate the unit away from sources of dust and dirt (like woodworking equipment), which can clog coils and grills. Observe all manufacturer warnings regarding electrical safety. In particular, never set up water drainage or disposal near electrical circuits or devices. Make sure the dehumidifier is connected to a properly grounded outlet. Keep drain hoses away from electrical cords and connections. If you are planning to use a hose to drain the dehumidifier’s water bucket, make sure the unit is located near enough to the floor drain or sump to avoid the need for a long and unwieldy hose. Do not create a tripping hazard! Do not be alarmed if the air temperature directly around the unit is warmer than in surrounding areas. As a dehumidifier removes moisture from the air, it slightly warms the space around it. Whole-house dehumidifiers are installed by your HVAC professional and are placed in a convenient location as part of your forced air system.
Operating Temperature
If the space being dehumidified has temperatures that typically fall below 65 degrees (F), you may want to consider buying a product that is specified for use at lower temperatures. Frost can form on the condensing coils if the air temperature drops below 65 degrees, and may negatively affect the performance of the product by causing the compressor to cycle on and off repeatedly without removing moisture from the air. If this happens, the unit should be switched off and allowed to defrost before it is turned back on. Some dehumidifiers come with an antifrost sensor, which will automatically turn the unit off if the air temperature drops below a certain point.
Relative Humidity (RH) and Humidistats
Many dehumidifiers include a built-in humidistat, a device that allows you to set the desired RH level. Once the room reaches the desired RH level, the dehumidifier will cycle on and off automatically to maintain the level. If your dehumidifier does not have a built-in humidistat, or has a humidistat that does not show RH levels, purchase a hygrometer (a gauge that measures relative humidity) separately and hang it near the dehumidifier. The hygrometer will measure RH levels and enable you to monitor when to turn the dehumidifier on and off.