By The Home Ventilating Institute (HVI)
Indoor air quality is often characterized by pollutants in the air. Clearly, if the sources of pollutants are minimized, the air will be easier to keep fresh, clean and healthy. In order to determine the best indoor-pollution control strategy, it is helpful to place airborne indoor contaminants into three categories:
1.Those released from materials inside the house;
2.Those brought into the house by air pressure differences; and
3.Those released by people.
Pollutants released from materials in the house
Many cleaning products and household furnishings release contaminants directly into the indoor air. Formaldehyde is often given off by kitchen cabinets. Wallpaper is treated with fungicides. The odor associated with some flooring materials may consist of over a hundred different volatile organic compounds (VOCs). Disinfectant and pesticide aerosol sprays typically contain hazardous ingredients.
The good news is that there are many alternative products on the market that are much more benign that can be used to build, furnish, and maintain our houses.
For pollutants that are unavoidable, a mechanical ventilation system that removes and expels them outdoors is essential to minimize their negative effect.
Pollutants brought indoors by air pressure differences
Some air pollutants originate outdoors but get brought indoors by air pressure differences. For example, when you turn on a clothes dryer, it blows a certain amount of air out of the house. This creates a slight negative pressure in the house, and an equal volume of air gets sucked in (infiltrates) from the outdoors through small gaps and cracks in the house. When a house is depressurized, the infiltrating air can bring in radon, termiticides, and biological pollutants such as mold. Particles or gases from insulation can also be sucked indoors by air pressure differences.
Combustion gases often migrate into the living space from a furnace, water heater, or wood stove, even though they are supposed to be expelled through a chimney. If the air pressure indoors is less than that outdoors, the gases will have difficulty going up the chimney and can remain in the house.
Pollutants released by human and animal metabolism
Human beings and pets give off a wide variety of pollutants. Our exhaled breath contains dozens of chemical compounds. These are normal by-products of our metabolism, and they all contribute to indoor air pollution. The best way to counteract the pollutants given off by people is to dilute the pollutants with ventilation air.
The concentration of “people pollutants” in a house depends on the number of people inside a house, the size of the house, and the behavior patterns (frequent showers, activity levels, and so on). People also bring pollutants indoors attached to their bodies, such as cigarette smoke, VOCs, perfume, and exhaust gases. Once contaminated clothing and bodies are indoors, the pollutants will be released slowly, contributing to indoor pollution. People can also track pollutants indoors on their shoes (e.g. lawn chemicals, animal waste, road dust containing asbestos, lead, rubber, etc.), and deposit those pollutants in carpeting and other surfaces.
Exchanging the air in a house is important to dilute the concentration of pollutants found in the indoor air. If indoor-pollutant concentrations are too high, they can negatively affect the health of occupants. Indoor air quality is improved by reducing or eliminating the source of pollutants, filtering, and supplying oxygen-rich, fresh air through mechanical ventilation.
With proper attention to reducing the sources of pollutants, the indoor air quality will be improved. The Home Ventilating Institute recommends the exclusive use of products which are HVI-Certified. Consult with your builder or contractor for appropriate HVI-Certified product for your application.
Adapted from: Understanding Ventilation: How to design, select, and install residential ventilation systems by John Bower © 2010 The Home Ventilating Institute (HVI).
• John P. Lapotaire, CIEC
• Certified Indoor Environmental Consultant
• Microshield Environmental Services, LLC