Kaz, Inc. is a manufacturer of humidifiers
thing that makes winter uncomfortable for humans, even inside
a nice warm building, is low humidity. People need a certain
level of humidity to be comfortable. In the winter, indoor
humidity can be extremely low and the lack of humidity can dry
out your skin and mucous membranes. Low humidity also makes
the air feel colder than it actually is. Dry air can also dry
out the wood in the walls and floors of our houses. As the
drying wood shrinks, it can cause creaks in floors and cracks
in drywall and plaster.
In this edition of HowStuffWorks,
you'll learn how a humidifier can help make things more
comfortable, and even save a little wear and tear on your
house by adding moisture to the air. It's surprising how big a
difference a little water can make!
Relative Humidity The relative humidity of
the air affects how comfortable we feel. But what is humidity,
and what is "relative humidity" relative to?
Humidity is defined as the amount of moisture in the
air. If you are standing in the bathroom after a hot shower
and can see the steam hanging in the air, or if you are
outside after a heavy rain, then you are in an area of high
humidity. If you are standing in the middle of a desert that
has not seen rainfall for two months, or if you are breathing
air out of a SCUBA tank,
then you are experiencing low humidity.
Air contains a certain amount of water vapor. The amount of
water vapor any mass of air can contain depends on the
temperature of that air: The warmer the air is, the more water
it can hold. A low relative humidity means that the air is dry
and could hold a lot more moisture at that temperature.
For example, at 20 degrees C (68 degrees F), a cubic meter
of air can hold a maximum of 18 grams of water. At 25 degrees
C (77 degrees F), it can hold 22 grams of water. If the
temperature is 25 degrees C and a cubic meter of air contains
22 grams of water, then the relative humidity is 100 percent.
If it contains 11 grams of water, the relative humidity is 50
percent. If it contains zero grams of water, relative humidity
is zero percent.
The relative humidity plays a large role in determining our
comfort level. If the relative humidity is 100 percent, it
means that water will not evaporate -- the air is already
saturated with moisture. Our bodies rely on the evaporation of
moisture from our skin for cooling. The lower the relative
humidity, the easier it is for moisture to evaporate from our
skin and the cooler we feel.
You may have heard of the heat
index. The chart below lists how hot a given temperature
will feel to us in various relative-humidity levels.
If the relative humidity is 100 percent, we feel much
hotter than the actual temperature indicates because our sweat
does not evaporate at all. If the relative humidity is low, we
feel cooler than the actual temperature because our sweat
evaporates easily; we can also feel extremely dry.
Low humidity has at least three effects on human
It dries out your skin and mucous membranes. If
your home has low humidity, you will notice things like
chapped lips, dry and itchy skin, and a dry sore throat when
you wake up in the morning. (Low humidity also dries out
plants and furniture.)
It increases static electricity, and most people
dislike getting sparked every time they touch something
It makes it seem colder than it actually is. In
the summer, high humidity makes it seem warmer than it is
because sweat cannot evaporate from your body. In the
winter, low humidity has the opposite effect. If you take a
look at the chart above, you'll see that if it is 70 degrees
F (21 degrees C) inside your home and the humidity is 10
percent, it feels like it is 65 degrees F (18 degrees
C). Simply by bringing the humidity up to 70 percent, you
can make it feel 5 degrees F (3 degrees C) warmer in your
Since it costs a lot less to humidify the air
than to heat it, a humidifier can save you a lot of money!
For best indoor comfort and health, a relative humidity of
about 45 percent is ideal. At temperatures typically found
indoors, this humidity level makes the air feels approximately
what the temperature indicates, and your skin and lungs do not
dry out and become irritated.
Most buildings can not maintain this level of humidity
without help. In the winter, relative humidity is often much
lower than 45 percent, and in the summer it is sometimes
higher. Let's see why this is.
Weather and Humidity
Here's what happens in winter to make it feel so dry in our
houses. Let's say that the outdoor temperature is 0 degrees C,
or 32 degrees F. The maximum amount of water that a cubic
meter of air can hold at this temperature is 5 grams. Now you
bring this cubic meter of air inside and heat it to 25 degrees
C or 77 degrees F. The relative humidity is only 23 percent:
5 grams of water in the air / 22 grams
possible = 23 percent relative humidity
It gets worse as the temperature outside falls lower. This
is why the air inside any heated building in the winter feels
so dry. Any time the temperature outside is below freezing,
relative humidity inside will be below 20 percent unless you
do something to increase the humidity.
The outside air might have a comfortable
level of humidity, but when that air is heated, the
relative humidity drops, causing the air to be very dry
During the dry months, a humidifier can help maintain a
comfortable level of humidity. Let's take a look at a simple
Inside a Humidifier The most common type of
humidifier is called an evaporative humidifier. This
type of humidifier is actually quite simple and, for the most
part, self-regulating. A reservoir holds cold water and
dispenses it into a basin. A wicking filter absorbs the
water from the basin. A fan then blows air through the
As the air passes through the filter, it evaporates some of
the water there. The higher the relative humidity, the harder
it is to evaporate water from the filter, which is why a
humidifier is self-regulating -- as humidity increases, the
humidifier's water-vapor output naturally decreases.
Sometimes an evaporative humidifier will be hooked up to
the heating and cooling system of a house or building. These
systems work in a similar way: A metal mesh or screen is
located in the duct coming from the furnace and/or air
conditioner; water from the building's pipes flows down the
screen; as air coming from the duct blows across the screen,
it picks up moisture.
Next we'll take a look at a few other types of humidifiers.
Types of Humidifiers There are many
different ways to raise the humidity in your home. For
example, you can put a pan of water on the stove or on the
radiator, or you hang wet towels near a heater duct. But most
people use a mechanical humidifier to do the job. Here
are the four most popular technologies:
KAZ V150 steam
Steam - Often referred to as a "vaporizer," a
steam humidifier boils water and releases the warm steam
into the room. This is the simplest, and therefore the least
expensive, technology for adding moisture to the air. You
can find inexpensive impeller models for less than $10 at
discount stores. Another advantage of this technology is
that you can use a medicated inhalant with the unit to help
KAZ V400 impeller humidifier
Impeller - In this humidifier, a rotating disc
flings water at a comb-like diffuser. The diffuser breaks
the water into fine droplets that float into the air. You
normally see these droplets as a cool fog exiting the
KAZ 5520 ultrasonic humidifier
Ultrasonic - An ultrasonic humidifier uses a
metal diaphragm vibrating at an ultrasonic frequency, much
like the element in a high-frequency speaker,
to create water droplets. An ultrasonic humidifier is
usually silent, and also produces a cool fog.
KAZ V3500 evaporative humidifier
Wick/Evaporative System - The wick system uses a
paper, cloth or foam wick or sheet to draw water out of the
reservoir. A fan blowing over the wick lets the air absorb
moisture. The higher the relative humidity, the harder it is
to evaporate water from the filter, which is why this type
of humidifier is self-regulating -- as humidity increases,
the humidifier's water-vapor output naturally decreases.
Here are some things to keep in mind as you are
weighing the advantages and disadvantages of the different
Steam vaporizers can be dangerous around children
because they can cause burns. They also have the highest
energy costs. However, there are no bacterial or mineral
concerns with this technology.
Impeller and ultrasonic designs have low energy costs
but raise two concerns. First, if the water gets stagnant,
these designs will spray the stagnant water, and any
bacteria it contains, into your home. This is why it is
important to clean the tank regularly and refill it with
clean water when you haven't been running it. Many high-end
ultrasonic units therefore have antibacterial features built
in. For example, some units use ultraviolet
light to kill bacteria.
The second concern is minerals in the water. Impeller and
ultrasonic designs send these minerals into the air. If the
water in your area contains a lot of minerals, you will
notice them as dust. The EPA
does not issue health warnings about minerals in the air,
but does recommend using low-mineral water (such as
distilled water) in your humidifier. Many ultrasonic models
feature a demineralization cartridge that filters minerals
out of the water to prevent the dust.
Some humidifiers monitor the relative humidity of the
air and will turn on and off as appropriate to maintain a
Humidifiers can be installed as small portable room
units, or they can be integrated into your furnace for
full-house humidity control.
If you are interested in tracking your home's humidity, an
inexpensive hygrometer will show you the relative
humidity in your house. You may be surprised to learn how low
For more information on humidifiers and related topics,
check out the links on the next page!