Aprilaire 700M Reference Manual page 7

This type of action goes
on, not only with wood,
but with every single
material in the home that
has the capacity to
absorb and release
moisture. Paper, plaster,
cloth, fibers, leather, glue,
skin, and practically
everything else in the home shrink as they lose water, and
swell as they take on water. If the water loss is rapid,
warping and cracking can take place. As the RH changes,
the condition and dimensions of the materials change, as
constantly as the weather. This is why humidity must be
added. This is why RH must be controlled. That is why
optimum RH is important.
What are the effects of this constantly changing or
constantly low moisture content in the air? Furniture
construction is affected as glue dries out, joints separate,
rungs fall out, and cracks appear. Plaster and drywall
dries out, resulting in unsightly cracks and popping nail
heads. Joists and studs shrink. Wood paneling separates
and cracks. Floors separate.
Pianos, organs, and other musical instruments lose their
tone. Pieces of art, books, and documents dry out and
can break or crack.
"
Increasing the humidity of your home helps eliminate the dry air that
can irritate and inflame the respiratory passages in the nose and
throat and can relieve the discomforts of colds and the flu.
– A.D.A.M. Health Encyclopedia
"
There is as yet no cure for the common cold. The most important
preventative measure would appear to be the proper regulation of
the humidity.
– Joseph Lubart, MD
New York State Journal of Medicine
"
Energy Conservation
Dry air robs the moisture from your skin, making you feel
colder, which means you turn up the heat. Dry air also
shrinks the framing around doors and windows, resulting
in gaps that let in cold air from the outside, making your
home less energy efficient.
The preservation benefit describes the change in the
dimension of wood with a change in the surrounding RH.
Heated air dries out and shrinks wood framing around
doors and windows. Outside air infiltrates the home at
these and additional locations, as a result of wind and
chimney or stack effect.
Studies suggest approximately
74% of a home's infiltration
occurs at the home's envelope
(perimeter walls, windows,
and doors). A published study
indicates the framing around
doors, windows, etc., will
have less shrinkage when
the proper inside RH is maintained. Therefore, proper
inside RH may reduce infiltration of outside air, because
the cracks between the framing and the supporting structure
will be reduced. With minimum shrinkage, there is less
crackage, reducing infiltration, thus increasing energy
conservation.
"