The
attic in your home needs ventilation. By dealing with this area-modifying
it in some way-you can cut heating and cooling bills sometimes by
as much as 50 percent. In this article we show you a basic way to
proper ventilation-how it's done-with a powered, roof-mounted attic
fan. But first, some basic background information about ventilation:
Summer
Heat/Ventilation-
In the summertime, the sun can cause the air inside an unvented
attic to reach temperatures of 150 degrees-and more. When this happens,
the insulation in the attic becomes a "heat sink," gradually absorbing
the heat until it obeys the laws of thermodynamics and moves to
the cooler living space below. Often this area is cooled by air
conditioning. So an attic temperature of 135-140 degrees may force
the air conditioner to run constantly to maintain 78 degrees in
the living area. The situation is nearly as bad as having no insulation
at all. The solution to the problem is ventilation that allows the
heated air to escape from the attic before it can build up. Aided
by a roof fan or ventilation that reduces the temperature in the
attic to 95 degrees, the air conditioner will run intermittently
and its costs will be from 10 to 30 percent less.
Winter
condensation-
In the winter, ventilation can remove humidity that moves through
the ceiling as water vapor. In the cold attic, the vapor condenses
in the insulation, which in turn loses most of its efficiency. In
extreme cases, icicles can hang from the rafters or the underside
of the roof.
When
the weather warms or the roof is heated to above freezing, the moisture
melts and soaks the insulation, possibly even leaking through the
ceiling to cause stains or damage. Finally, this moisture will reveal
itself in the form of rot or other structural damage to your home.
Vapor barriers are designed to prevent this process, but many homes
do not have ceiling vapor barriers and, in any event, you cannot
be assured that they will be 100 percent effective.
Ventilation
is just as important in the winter as it is in the summer, but for
different reasons.
How
to ventilate attics-
Natural ventilation relies on fixed non-powered devices called ventilators,
or "vents." These are located in openings in the attic-or other
space to be ventilated-to take advantage of the natural flow of
air. Cool air enters the lower vents, is warmed, then rises and
moves out the upper vents to expel both heat and humidity.
Powered
ventilation relies on turbine ventilators, electrically powered
exhaust fans mounted on the roof or in the attic, or on ceiling-mounted
whole house exhaust fans. Powered fans require sufficient vent areas
in the roof to allow the air to be pulled, or exhausted, from the
attic space.
How
much ventilation?-
To determine how much ventilation is needed for your home, either
natural or powered, you need to know the square footage of the attic.
Then you can match the fixture to the free area needed for the ventilation
system that you need.
