LEARN MORE AT
energystar.gov
ENERGY STAR®, a U.S. Environmental Protection Agency
program, helps us all save money and protect our environment
through energy efficient products and practices. For more
information, visit www.energystar.gov.
Mechanical Ventilation
Breathe Easy with Fresh Air in the Home
Without mechanical ventilation to provide fresh air, moisture, odors, and other
pollutants can build up inside a home. Mechanical ventilation systems circulate fresh
air using ducts and fans, rather than relying on airflow through small holes or cracks
in a home's walls, roof, or windows. Homeowners can breathe easier knowing their
home has good ventilation.
BENEFITS OF MECHANICAL VENTILATION
• Better Indoor Air Quality. Indoor air can be many times more polluted than outdoor air, and
the average American spends 90 percent of the day inside. Ventilation systems can
significantly improve a home's air quality by removing allergens, pollutants, and moisture
that can cause mold problems.
•	More Control. When homes rely on air flow through walls, roofs, and windows for
ventilation, there is no control over the source or amount of air that comes into the house.
In fact, air leaking into the house may come from undesirable areas such as the garage,
attic, or crawl space. Mechanical ventilation systems, however, provide proper fresh air
flow along with appropriate locations for intake and exhaust.
•	Improved Comfort. Mechanical ventilation systems allow a constant flow of outside air
into the home and can also provide filtration, dehumidification, and conditioning of the
incoming outside air.
HOW VENTILATION SYSTEMS WORK
A variety of mechanical ventilation systems are available to select from, based on local climate
and the home's heating and cooling system. In addition to one of the primary systems
described below, "spot" ventilation fans should also be provided for kitchens and baths to
remove the concentrated moisture and odors that can occur in these rooms. The typical
systems and recommended climates are described below:
• Supply Ventilation Systems —Hot or Mixed Climates. Fresh air is drawn in through an air
"intake" vent and distributed to many rooms by a fan and duct system. A fan and set of
ducts dedicated solely to ventilation can be used, or an outside air intake can be
connected to the main return air duct, allowing the heating and cooling system's fan and
ducts to distribute the fresh air. The benefit of connecting to the return air duct is that
outdoor air can be air conditioned or dehumidified before it is introduced into the home.
Because supply systems continually introduce outdoor air, a home can become slightly
pressurized. As a result, these systems are typically not appropriate for cold climates

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where there is a risk of heated indoor air being pushed through any remaining holes and
cracks in the construction assembly where it could reach cold exterior surfaces, condense,
and cause moisture problems.
•	Exhaust Ventilation Systems—Cold Climates. Indoor air is continuously exhausted to the
outdoors with one or more fans often located in bathrooms. Because indoor air is
continually drawn out, the home becomes slightly depressurized. As a result, these
systems are typically not appropriate for hot, humid climates where there is a risk of
drawing hot outdoor air into remaining holes and cracks in the construction assembly
where it could reach cool interior surfaces, condense, and cause moisture problems.
•	Balanced Ventilation Systems—All Climates. With these
systems, equal quantities of air are brought into and
sent out of the home. This is usually achieved using
two fans—one to bring fresh air in and another to send
indoor air out. The two most common systems are
"heat recovery" ventilation (commonly referred to as
HRV) and "energy recovery" ventilation (commonly
referred to as ERV). HRVs transfer heat from exhaust
air to incoming air during the heating season and from
incoming air to exhaust air in the air conditioning
season to reduce the heating and cooling load and
improve comfort. ERVs transfer heat and moisture
between the exhaust air and incoming air. This provides additional savings in the summer
by reducing the moisture content of the incoming air that would otherwise have to be
dehumidified with the cooling equipment or a dehumidifier. ERVs also provide additional
comfort in the winter by adding moisture from the outgoing air to the incoming air to help
avoid excessively dry indoor conditions.
A BETTER FUTURE
ENERGY STAR is a voluntary partnership between the government and more than 9,000
organizations, including more than 3,500 of the nation's home builders. Together with home
buyers and their families, we are working to achieve a common goal —protecting the
environment for future generations by changing to more energy-efficient practices and
products today.
ENERGY STAR is the government-backed symbol for energy efficiency. It identifies new
homes, buildings, and more than 50 types of products that are energy efficient and offer the
features, quality, and performance that today's consumers expect. Products that can earn the
ENERGY STAR include windows, heating and cooling equipment, lighting, and appliances. To
learn more about ENERGY STAR, visit www.energystar.gov.

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