US EPA guidance on indoor air quality, radon and mold

Why indoor air deserves attention

According to EPA's The Inside Story, the air inside homes and other buildings can be more seriously polluted than outdoor air, even in large industrialized cities. Since people spend approximately 90 percent of their time indoors, the health risks from indoor air may be greater for many people than those from outdoor air.

Pollutants come from combustion appliances, tobacco smoke, building materials, household products and furnishings. When there is little infiltration or ventilation, the air exchange rate is low and pollutant levels can build up. Immediate effects include irritation of the eyes, nose and throat, headaches, dizziness and fatigue.

The guide also points to combustion as a frequent source: an improperly adjusted gas stove, for example, can emit significantly more carbon monoxide than a properly adjusted one, and gases and particles can come from poorly maintained chimneys, flues and cracked furnace heat exchangers.

Three basic strategies: source control, ventilation, air cleaning

EPA states that the most effective way to improve indoor air is usually to eliminate sources of pollution or reduce their emissions. Some sources can be sealed or enclosed, others, like gas stoves, can be adjusted. Source control is often more cost-efficient than increasing ventilation.

Ventilation comes next. Most home heating and cooling systems do not mechanically bring fresh air into the house, so opening windows when the weather permits and using bathroom or kitchen fans that exhaust outdoors help, especially while painting, cooking or sanding. Air cleaning is a supplement to these two steps, not a replacement.

For new construction, EPA notes that advanced home designs are starting to include mechanical systems that bring outdoor air inside, some with energy-efficient heat recovery ventilators (also called air-to-air heat exchangers).

Radon: the basics of testing and fixing a home

Radon is a radioactive gas you cannot see, smell or taste. It enters through cracks and openings in the foundation, and sometimes through well water, and any home can have a radon problem: EPA estimates that nearly one out of every 15 homes in the United States has an elevated level (4 pCi/L or more). The Surgeon General has warned that radon is the second leading cause of lung cancer in the United States, after smoking.

EPA recommends fixing a home at 4 picocuries per liter (pCi/L) or higher. Short-term tests stay in place two to 90 days; long-term tests more than 90 days and better reflect the year-round average. A first short-term result of 4 pCi/L or more calls for a follow-up test.

The main fix is a soil suction system: a vent pipe and fan that pull radon from beneath the house and vent it outside. Some systems reduce levels by up to 99%.

Indoor air quality in offices and commercial buildings

EPA's Building Air Quality guide names four elements behind IAQ problems: a source of contamination or discomfort, an HVAC system that cannot control existing contaminants and ensure thermal comfort, pathways connecting the source to occupants, and the occupants themselves.

It recommends designating an IAQ manager and building an IAQ profile in three stages: review existing records, conduct a walkthrough inspection, then collect detailed information on the HVAC system, pathways, sources and occupancy. Peak carbon dioxide over 1000 ppm indicates underventilation. Complaints may also stem from noise, lighting or ergonomic stress rather than air.

The guide warns that limiting operating costs by reducing ventilation can be a false economy if it leads to more occupant complaints, reduced productivity and absenteeism. Every complaint merits a response, and if problems persist after careful application of the guidance, outside help will probably be needed.

Frequently asked questions