Ventilation and Health

ASHRAE Standard 62.2 is written to provide "acceptable indoor air quality" – not "healthy indoor air". Here's ASHRAE's definition of "acceptable indoor air quality":

...air toward which a substantial majority of occupants express no dissatisfaction with respect to odor and sensory irritation and in which there are not likely to be contaminants at concentrations that are known to pose a health risk.

Historically, acceptable indoor air quality (IAQ) was based on focus groups where 80% of the participants did not complain about odors or irritation. Over time, language was added about known health risks from contaminants, but compliance with ASHRAE Standard 62.2 does not guarantee healthy indoor air quality. Rather, it is a consensus document on residential ventilation that will result in acceptable indoor air quality for most people in most situations. For this reason, consider ASHRAE Standard 62.2 a minimum standard for ventilation.

It would be great to establish simple ventilation rules to ensure healthy air in every home. Unfortunately, standardization is difficult because indoor air quality and ventilation needs vary greatly.

  • Occupancy: A house or apartment with one occupant has different ventilation needs than a household of five or more.
  • Occupant susceptibility: Some people are more susceptible than others to contaminants. Pollutant levels that cause an asthma attack in one person may cause no problems for someone else.
  • Building characteristics: The size, shape, design, and materials used in a building affect air leakage rates and pollutant sources.
  • Pollutant load: Each house and apartment has different sources and levels of indoor pollutants.
  • Weather: Temperature, wind, and humidity vary throughout the year in any single location and in different climate zones. Each of these weather factors affects indoor air quality.

What Are the Sources of Indoor Pollutants?

Most homes have many sources of indoor contaminants that are constantly released into the air, including:

  • carbon dioxide, moisture, and odors produced by people and pets
  • moisture from other sources (such as plants and aquariums)
  • pollutants from the activities and contents in the home, or brought into the home on the bottoms of shoes
  • pollutants from building materials

Whole-building ventilation is designed to continuously dilute and remove contaminants to provide "acceptable indoor air quality" whenever people are present.

Temporary activities in a household may significantly raise levels of indoor contaminants. The ASHRAE Standard does not address high-polluting events, such as:

  • painting
  • cleaning with strong cleaning products
  • smoking
  • the use of unvented combustion space heaters such as portable kerosene heaters (which are no longer allowed in California)

Whenever Possible, Remove the Sources of Indoor Pollution

The goal of ventilation requirements is to improve indoor air quality through the installation of mechanical ventilation. Good ventilation helps, but an effective way to improve air quality in a home is to control pollution sources.

  • Building maintenance. Serious pollutants can result from water leaks and high levels of moisture in homes. Unresolved water and moisture problems can lead to mold and expensive repairs.
  • Occupant education. Many pollutants are unintentionally introduced to the home by occupants. Teach occupants to avoid products that pollute indoors such as air fresheners, candles, harsh cleaning supplies, and highly fragrant consumer products and cosmetics. Teach them how and when to operate the ventilation equipment that you install.
  • Construction materials. In most remodeling and building repair projects, significant pollution can be introduced by new building materials, adhesives, flooring, paint, carpeting, and finishes. Choose materials carefully to avoid adding pollutant sources.

What Health Problems are Associated with Poor Indoor Air Quality?

  • The Environmental Protection Agency provides an online Introduction to Indoor Air Quality that includes the health effects of exposure to many household pollutants, including asbestos, carbon monoxide, formaldehyde, nitrogen dioxide, pesticides, radon, secondhand smoke, and volatile organic compounds (VOCs).
  • The U.S. Surgeon General has concluded that there is no risk-free level of secondhand smoke. Breathing secondhand smoke is especially harmful to infants and children, who are more at risk for weakened lungs, bronchitis, pneumonia, ear infections, and sudden infant death syndrome. Children with asthma experience more frequent and severe attacks.
  • Nonsmokers who breathe secondhand smoke are at increased risk for lung cancer and cardiovascular disease.
  • Dampness and mold in buildings raise the risks of asthma and other respiratory conditions in adults and children.

Most of the pollutants of concern indoors not listed above are also pollutants that have been of concern outdoors or in industrial settings. Significant toxicological (controlled studies on the health impacts of exposure of specific chemicals on animals) and epidemiological (studies of lifelong disease impact of atmospheric or work-related exposure to humans unintendedly exposed) data exist for many compounds linking high exposure to specific health endpoints. In homes, people are exposed to a mixture of chemicals over the course of a lifetime. While it is not clear what the impact of this mixture is, the individual compounds found in indoor air have been associated with cancer, respiratory issues, and early mortality, among other endpoints.

The key to providing good indoor air quality is to remove the pollutants generated in the indoors without bringing in more pollutants from the outdoors. Ventilation can remove or dilute indoor pollutant emissions, but care must be taken to not bring in harmful pollutants from outdoors.