Glossary and Terms

Read more about home improvement, see "Improve Your Home’s Energy Efficiency with ENERGY STAR"

Also, read "The Inside Story: A Guide to Indoor Air Quality"

ACH. Air changes per hour. The amount of air in a building that leaks out or is removed by a fan and is replaced by outdoor air. Usually listed as a fraction of one air change per hour, such as .35 ACH.

Action level for radon. EPA recommends home owners take action to lower radon levels indoors when concentrations are above 4 pCi/L.

Air Cleaning. An IAQ control strategy to remove various airborne particulates and/or gases from the air. The three types of air cleaning most commonly used are: particulate filtration (e.g., most common furnace filters), electrostatic precipitation, and gas sorption.

Air Exchange Rate. The rate at which outside air replaces indoor air in a space. Expressed in one of two ways: the number of changes of inside air per unit of time -- air changes per hour (ACH); or the rate at which a volume of outside air enters per unit of time -- cubic feet per minute (cfm).

Air Handling Unit (AHU). For purposes of this website, this refers to equipment that includes a blower or fan, heating and/or cooling coils, and related equipment such as controls, condensate drain pans, and air filters. Does not include ductwork, registers or grilles, or boilers and chillers.

Allergen. Something--including biological material such as fungi, mold, spores, insect parts, skin flakes, and chemical compounds--which causes an allergic reaction.

Animal Dander. Tiny scales of animal skin.

Arrestance. The ability of a filter to remove injected standard dust from the test air.

ASHRAE. American Society of Heating, Refrigerating, and Air-Conditioning Engineers is an international group which is organized for the purpose of advancing the arts and sciences of heating, ventilation, air conditioning and refrigeration through research, standards writing, continuing education and publications.

ASTM. American Society for Testing and Materials, a consensus-based standard setting organization.

Backdrafting. A condition caused by negative pressure in the home in which the exhaust from combustion equipment such as hot water heaters, fireplaces, or furnaces, is sucked back down the flue and into the house.

Biological Contaminants. Agents derived from, or that are, living organisms (e.g., viruses, bacteria, fungi, pollen, and mammal and bird antigens) that can be inhaled and can cause many types of health effects including allergic reactions, respiratory disorders, hypersensitivity diseases, and infectious diseases. Also referred to as "microbials" or "microbiologicals".

Building Code. Criteria or requirements (i.e., minimum standards) set forth and enforced by a state or local agency for the protection of public health and safety. Is usually based on a model code (see below) and/or Model Standards published by acknowledged organizations or associations.

Building-Related Illness A discrete, identifiable disease or illness that can be traced to a specific pollutant or source within a sick building. (Contrast with "Sick Building Syndrome").

Carbon Dioxide. Carbon Dioxide (CO₂) is a colorless, odorless, and tasteless product of combustion. All combustion processes and human metabolic processes are sources of CO₂. Concentrations of CO₂ from people are always present in all occupied buildings, and at concentrations normally found in buildings, CO₂ is not a health hazard.

Carbon Monoxide. Carbon Monoxide (CO) is a colorless, odorless, and tasteless gas which results from combustion of fuels. It is often associated with combustion heating devices (e.g. boilers, furnaces) and auto, truck, or bus exhaust from attached garages, nearby roads, or parking areas. At moderate concentrations, angina, impaired vision, and reduced brain function may result. At higher concentrations, CO exposure can be fatal.

CDC. The Centers for Disease Control and Prevention is an agency of the Department of Health and Human Services whose mission is to promote health and quality of life by preventing and controlling disease, injury, and disability. See www.cdc.gov

CFM. Cubic feet per minute. The amount of air, in cubic feet, that flows through a given space in one minute.

CO. Carbon Monoxide.

CO₂. Carbon Dioxide.

Combustion Air. Air that is supplied to combustion appliances to be used in the combustion of fuels and the process of venting combustion gases. Inadequate combustion air can lead to dangerous problems.

Condensation. The transformation of the water vapor content of the air into liquid water on cold surfaces. The beads or drops of water (or frost in extremely cold weather) that accumulate on the inside of the exterior covering of a building when warm, moisture-laden air from the interior reaches a point where the temperature no longer permits the air to sustain the moisture it holds.

Conditioned Air. Air that has been heated, cooled, humidified, or dehumidified. (Sometimes referred to as "tempered" air.)

Conditioned Space. The part of the home that is meant to be heated and/or cooled. Typically includes the living area; may or may not include unfinished basements, crawlspaces, and attics.

Damper. A device used to vary airflow through an air duct. A damper may be immovable, manually adjustable, or part of an automated system.

Dampproofing. Sealing the foundation walls to help prevent outside moisture from entering the basement.

Disinfectants. One of three groups of anti-microbials registered by the EPA for public heath uses. EPA considers an anti-microbial to be a disinfectant when it destroys or irreversibly inactivates infectious or other undesirable organisms, but not necessarily their spores.

Drain Tile Loop. Typically refers to a length of perforated pipe extending around all or part of the perimeter of a home's foundation. This provides drainage to prevent water from entering the home.

Drain Trap. A dip in the drain pipe of sinks, toilets, floor drains, etc., which is designed to stay filled with water, thereby preventing sewer gases from escaping into the room.

Dust spot efficiency. A measure of the ability of a filter to remove atmospheric dust from air (expressed in percent).

EPA. United States Environmental Protection Agency.

ETS. Environmental Tobacco Smoke. Also referred to as "Secondhand Smoke".

Exhaust Ventilation. Mechanical removal of air from a portion of a building (e.g., from a bathroom fan, kitchen range hood, clothes dryer, or central exhaust fan).

Exposure. The initial contact of the body with a substance.

Flashing. Material for allowing proper drainage around the joints and angles of the roof and penetrations through the roof and walls.

Footing. The supporting base for the foundation walls.

Formaldehyde. Formaldehyde is a colorless water-soluble gas. Due to its wide use, it is frequently considered separately from other VOCs. Materials containing formaldehyde include building materials, furnishing, and some consumer products. Formaldehyde has a pungent odor and is detected by many people at levels of about 100 parts per billion (ppb). Besides the annoyance, it also causes acute eye burning and irritates mucous membranes and the respiratory tract. EPA has determined formaldehyde to be a probable human carcinogen.

HEPA. High efficiency particulate arrestance (filters).

HVAC. Heating, ventilation, and air-conditioning system.

IAQ. Indoor air quality.

Indoor Air Pollutant. Particles, dust, fibers, mists, bioaerosols, and gases or vapors which can cause a variety of health effects and problems in a building.

Integrated Pest Management. Use of, as appropriate to the pest and its environment, mechanical, physical, chemical, or biological procedures to prevent unacceptable levels of pest activity and damage by the most economical means with the least possible hazard to people, property, and the environment.

IPM. Integrated Pest Management.

Local Exhaust. Fans used to exhaust pollutants and moisture at or near their source. Bath fans, range hoods, and utility room fans are all examples of local exhaust.

Make-up Air. See "Outdoor Air Supply".

Map of Radon Zones. EPA's Map of Radon Zones assigns each of the 3,141 counties in the United States to one of three zones based on radon potential.

Mechanical Ventilation. Ventilation from the operation of a fan, either exhausting air from a house, supplying air, or both.

Microbiologicals. See "Biological Contaminants".

Multiple Chemical Sensitivity. A condition in which a person is considered to be sensitive to a number of chemicals at very low concentrations. There are a number of views about the existence, potential causes, and possible remedial actions regarding this condition.

Natural Ventilation. The movement of air into and out of a home through random holes and cracks, and open windows and doors. The air movement is caused by wind and by temperature differences (which drives the stack effect).

NIOSH. National Institute for Occupational Safety and Health is part of the Centers for Disease Control and Prevention (CDC) and is the only federal Institute responsible for conducting research and making recommendations for the prevention of work-related illnesses and injuries. See www.cdc.gov/niosh

Negative Pressure. Condition that exists when less air is supplied to a space than is exhausted from the space, so the air pressure within that space is less than that in surrounding areas. Under this condition, if an opening exists, air will flow from surrounding areas into (and not out of) the negatively pressurized space.

Off-gassing. The production of gases from the chemical deterioration of a substance over time, and the release of gases from materials into the air.

Outdoor Air Supply. Air brought into a building from the outdoors (often through the ventilation system) that has not been previously circulated through the system.

Passive Radon-Reduction System. Short for "passive sub-slab depressurization system". Approach for reduction of radon levels which utilizes barriers to radon entry and stack effect reduction techniques to reduce the rate of radon entry, plus the installation of a PVC pipe running from beneath the slab to the roof to vent radon gas.

pCi/l. Picocuries per liter (of air), unit for measuring radon concentrations. The EPA Action Level for indoor radon is 4 pCi/L.

Picocurie. A unit for measuring radioactivity, often expressed as picocuries per liter of air (pCi/l).

PPB. Parts per billion.

PPM. Parts per million.

Plenum. Air compartment connected to a series of ducts. For example, a ceiling plenum is the space above the suspended ceiling and below the floor above that is used as part of the air distribution system.

Pollutant Pathways. Avenues for distribution of pollutants in a buildings. HVAC systems are the primary pathway in most buildings; however, all building components interact to affect how air movement distributes pollutants.

Positive Pressure. Condition that exists when more air is supplied to a space than is exhausted from the space, so the air pressure within that space is more than that in surrounding areas. Under this condition, if an opening exists, air will flow from the positively pressurized space into surrounding areas.

Preventive Maintenance. Regular and systematic inspection, cleaning, and replacement of worn parts, materials, and systems. Preventive maintenance helps to prevent parts, materials, and systems failure by ensuring that parts, materials, and systems are in good working order.

Radon. A colorless, odorless, radioactive gas that occurs naturally in soil and rock. Radon migrates through the soil and groundwater and can enter buildings through cracks or other openings in the foundation. Radon can also enter well water. Exposure to airborne radon can cause lung cancer. EPA recommends home owners take action to lower radon levels indoors when concentrations are above 4 pCi/L.

Re-entry/Re-entrainment. Situation that occurs when the air being exhausted from a building is brought back into the system through the air intake and other openings in the building envelope.

Sanitizer. One of three groups of anti-microbials registered by the EPA for public heath uses. EPA considers an anti-microbial to be a sanitizer when it reduces but does not necessarily eliminate all the microorganisms on a treated surface.

Short-circuiting. Situation that occurs when the supply air flows to return or exhaust grilles before entering the breathing zone (area of a room where people are).

Sick Building Syndrome. Term sometimes used to describe situations in which building occupants experience acute health and/or comfort effects that appear to be linked to time spent in a particular building, but where no specific illness or cause can be identified. The complaints may be localized in a particular room or zone, or may be spread throughout the building.

Soil Gases. Gases that enter a building from the surrounding ground (e.g., radon, volatile organic compounds, gases from pesticides in the soil).

Soil-Gas-Retarder. A continuous membrane of 6-mil polyethylene or equivalent material used to retard the flow of soil gases into a building. (In radon-resistant construction, the membrane also prevents the concrete from flowing into the gravel and blocking some air flow beneath the slab.)

Sones. The sone is a linear unit (measure) of loudness which allows a simplified comparison of fan loudness. For example, a fan which is 3.0 sones is three times as loud as a fan at 1.0 sones.

Sources. Sources of indoor air pollutants. Indoor air pollutants can originate within the building or can be drawn in from outdoors. Common sources include people, room furnishings (such as carpeting), photocopiers, art supplies, etc.

Spot Ventilation. See "local exhaust".

Stack Effect. The flow of air that results from warm air rising, creating a positive pressure area at the top of a building and a negative pressure area at the bottom of a building. The stack effect can overpower the mechanical system and disrupt ventilation and circulation in a building.

Sterilizer. One of three groups of anti-microbials registered by the EPA for public heath uses. EPA considers an anti-microbial to be a sterilizer when it destroys or eliminates all forms of bacteria, fungi, viruses, and their spores.

Sub-Slab Depressurization. A system designed to achieve lower sub-slab air pressure relative to indoor air pressure (used in radon control and mitigation). May be a passive system (no fan) or an active system (with fan).

TVOCs. Total volatile organic compounds. See "Volatile Organic Compounds (VOCs)".

VOCs. See "Volatile Organic Compounds".

Volatile Organic Compounds (VOCs). Compounds that vaporize (become a gas) at room temperature. Common sources which may emit VOCs into indoor air include housekeeping and maintenance products, and building and furnishing materials. In sufficient quantities, VOCs can cause eye, nose, and throat irritations, headaches, dizziness, visual disorders, memory impairment; some are known to cause cancer in animals; some are suspected of causing, or known to cause, cancer in humans.

Zone. The occupied space or group of spaces within a building which has its heating or cooling controlled by a single thermostat.

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