Indoor Ventilation: Overview
If too little outdoor air enters a home,
pollutants can accumulate to levels that can pose health and
Unless they are built with special mechanical means of ventilation,
homes that are designed and constructed to minimize the amount
of outdoor air that can "leak" into and out of the
home may have higher pollutant levels than other homes. However,
because some weather conditions can drastically reduce the
amount of outdoor air that enters a home, pollutants can build
up even in homes that are normally considered "leaky."
How Does Outdoor Air Enter a House?
Outdoor air enters and leaves a house by: infiltration, natural
ventilation, and mechanical ventilation. In a process known
as infiltration, outdoor air flows into the house through
openings, joints, and cracks in walls, floors, and ceilings,
and around windows and doors. In natural ventilation, air
moves through opened windows and doors. Air movement associated
with infiltration and natural ventilation is caused by air
temperature differences between indoors and outdoors and by
wind. Finally, there are a number of mechanical ventilation
devices, from outdoor-vented fans that intermittently remove
air from a single room, such as bathrooms and kitchen, to
air handling systems that use fans and duct work to continuously
remove indoor air and distribute filtered and conditioned
outdoor air to strategic points throughout the house. The
rate at which outdoor air replaces indoor air is described
as the air exchange rate. When there is little infiltration,
natural ventilation, or mechanical ventilation, the air exchange
rate is low and pollutant levels can increase.
What If You Live in an Apartment?
Apartments can have the same indoor air problems as single-family
homes because many of the pollution sources, such as the interior
building materials, furnishings, and household products, are
similar. Indoor air problems similar to those in offices are
caused by such sources as contaminated ventilation systems,
improperly placed outdoor air intakes, or maintenance activities.
Solutions to air quality problems in apartments, as in homes
and offices, involve such actions as: eliminating or controlling
the sources of pollution, increasing ventilation, and installing
air cleaning devices. Often a resident can take the appropriate
action to improve the indoor air quality by removing a source,
altering an activity, unblocking an air supply vent, or opening
a window to temporarily increase the ventilation; in other
cases, however, only the building owner or manager is in a
position to remedy the problem. You can encourage building
management to follow guidance in EPA and NIOSH's Building
Air Quality: A Guide for Building Owners and Facility Managers.