Proper ventilation helps improve indoor
air quality. Ventilation can control indoor humidity and airborne contaminants,
both of which either contribute to or act as health hazards.
High indoor humidity can spur mold
growth. High humidity may result from poor construction or rehabilitation,
site design that does not properly manage water, and/or inadequate air
exchange. A reasonable target for relative humidity is 30-60 percent.
A low cost hygrometer, available at hardware stores, can be used to measure
relative humidity. In cool climates, inadequate ventilation in the winter
can contribute to excessive moisture and humidity because normal activities
create moisture (cooking, bathing, breathing), and there is insufficient
natural ventilation (opening windows) or mechanical ventilation (fans,
exhaust systems) to remove the moisture.
In warmer climates, the heating, ventilation, and air conditioning (HVAC)
system can pull warmer, humid air inside. In this case, the ventilation
system may help create indoor humidity problems unless the system also
dehumidifies the air.
Indoor contaminants. These include chemicals used in
the construction or renovation of buildings (e.g., glues, off-gassing
from carpets, emissions from particle board, cleaning compounds). In addition,
appliances that burn gas can produce particulates and carbon
monoxide. Incomplete combustion and poor ventilation of these
appliances (cook stoves, gas furnaces, gas boilers, and gas water heaters)
can contribute to indoor contaminants. Gas cook tops should be used with
fans that send exhaust outside. Gas-fired heating appliances should be
sealed and power-vented systems installed to remove products of incomplete
combustion. Wood-burning stoves can also create particulates and must
be vented outside.
Outdoor contaminants. Outdoor particulates can be drawn
inside when the heating or cooling system draws air into a home. Particulates
and allergens found in outdoor air can be asthma
triggers. Filtering incoming air for HVAC systems effectively filters
particulates. Experts recommend using filters with a MERV 6-8, but higher
MERV levels trap smaller particles and generally are more appropriate
for those with allergies or where the indoor environment has a high concentration
of mold spores, dust particles, or other allergens.
Two types of ventilation can help control harmful air contaminants and
humidity: spot ventilation and dilution ventilation. Spot ventilation
draws air from a particular location (e.g., bathroom, kitchen) and exhausts
it to the outside. Dilution ventilation address low-level contamination
throughout the home.
Spot Ventilation. Exterior exhaust fans should be installed
in all bathrooms and kitchens. These fans remove humidity and carbon monoxide.
The most effective fans are quiet and durable. Use fans that operate at
one sone or less and exhaust to the outdoors. Fans equipped with timers
or de-humidistat controls are useful to ensure the fans run for a sufficient
period of time. A good rule of thumb is to run a bathroom fan for about
45 minutes after a shower.
Dilution Ventilation. Dilution ventilation addresses
the entire living space. Air changes (exchanging indoor air with outdoor
air) and air cleaning help determine the effectiveness of dilution. Air
changes result from a combination of natural ventilation (infiltration;
leakage; windows) and mechanical (controlled) ventilation. Air cleaning
occurs when particulates are filtered and when air is dehumidified to
remove moisture. The goal is to provide sufficient changes to ensure a
healthy environment. There are several types of heating and cooling systems
with filtration that can be installed to accomplish this. A common element
necessary in all systems is duct sealing, particularly on the return side
(side drawing in the air). The Air Conditioning Contractors Association
(ACCA) provides guidance on duct sealing in its Manual D: Duct Design.
It is important not to oversize a system. Oversizing can contribute
to poor air distribution and insufficient dehumidification, creating an
environment that promotes mold growth. Oversized heating systems can “short
cycle,” meaning that the system does not run long enough to turn
the fan on for a sufficient period to distribute new air. Systems that
short cycle during air conditioning will deliver cold air in short bursts
but not necessarily dehumidify the air. The resulting cold, clammy environment
can encourage mold growth. Some contractors oversize HVAC systems to compensate
for duct leakage and to minimize complaints about heating or cooling delivery.
The ACCA provides guidance on system sizing in its Manual J.
HVAC systems can also exacerbate indoor air quality problems. The HVAC
system may be contaminated (because of mold in duct lining or bacteria
on coil or filters, for example), and the system may spread these pollutants
throughout the home. Second, the HVAC duct distribution system can spread
pollutants from one portion of the home to another. Regular maintenance
and duct sealing can help minimize these problems.
The American Society of Heating, Refrigerating, and Air Conditioning
Engineers (ASHRAE) and several states (Minnesota, Washington, and Vermont)
have ventilation standards designed to ensure acceptable indoor air quality.
Alliance for Healthy Homes
Contractors of America
of Heating and Refrigerating and Air Conditioning Engineers, Inc.
Science Corporation - READ
THIS: Before You Ventilate
Minnesota - Mechanical
Ventilation Systems (Minnesota's amendments to the International
Residental Code, Chapter 11)
Washington - Washington Administrative Code: Ventilation
and Indoor Air Quality, 2006
- General IAQ Hotline (IAQINFO): 1-800-438-4318
Sponsored by EPA, this hotline provides general information on indoor
air quality and related pollutants.
- Su Familia (Your Family): 1-866-SU FAMILIA
Alliance for Hispanic Health sponsors this helpline to
offer Hispanic consumers free, reliable and confidential health information
in Spanish and English and help navigate callers through the health