Ventilation A to Z

A       B       C       D       E       F       G       H
I       J       K       L       M       N       O       P       Q       R
S       T       U       V       W       X       Y       Z

- A -

Absolute Humidity: The weight of water vapor in a given volume of air.

Accidental Ventilation: Random air movement into and out of a house.

Active Ventilation: See Mechanical Ventilation.

Air Barrier: Material(s) assembled and joined together to provide a barrier to air leakage through the building envelope. An air barrier may be a single material or combination of materials.

Air Changes per Hour (ACH): The number of times the volume of air in a house is replaced with outdoor air during one hour.

Air Cleaner: A filtering device for removing impurities and particulates from air.

Air distribution: Movement of air throughout a house with a ventilation system or heating/cooling system.

Air Filter Efficiency: The ability of a device to remove particulate or gaseous material from an airstream by measuring the concentration of the material upstream and downstream of the device. See also MERV rating.

Air Handler: An Air Handling Unit (most commonly abbreviated AHU), or Air Handler, is a central air conditioner station that distributes the air that will be supplied to the building by the ventilation ductwork.

Air Sealing: Air sealing is the systematic locating and sealing of air leakage points throughout your home, creating a barrier between conditioned and non-conditioned spaces.

Air-to-Air Heat Exchanger (AAHX): Air exchange systems that help to enhance indoor air quality and minimize heating and/or cooling costs. They retain existing heat and optimize the interior moisture content in the air. These mechanical systems use fans to maintain a balanced airflow into the house while exhausting stale indoor air. See Energy Recovery Ventilator and Heat Recovery Ventilator.

Airtight Construction: Building techniques that result in a house with a small effective leakage area (ELA) to conserve energy.

Airtight Drywall Approach (ADA): A construction practice that utilizes the airtight characteristics of drywall to provide an air barrier. To complete the barrier, the perimeter and penetrations through the drywall must be sealed.

AMCA Air Movement and Control Association (AMCA): A not-for-profit association of manufacturers of commercial fans, louvers, dampers, air curtains, air flow measurement devices, ducts, acoustic attenuators and other air system components.

American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE): An international technical society organized to advance the arts and sciences of heating, ventilation, air-conditioning and refrigeration.

Apparent Sensible Effectiveness (ASEF): Term used in the CSA C439M standard for testing HRVs to describe the temperature rise of the outdoor air passing through an HRV. The measured temperature rise of the supply airstream divided by the difference between the outdoor temperature (point 1) and entering exhaust system air temperature (point 3), then multiplied by the ratio of mass flow rate of the supply airflow divided by the mass flow rate of the lower of the supply or exhaust system airflows. Apparent Sensible Effectiveness is useful to predict final delivered air temperature at a given flow rate and should be used for energy modeling when wattage for air movement is separately accounted for in the energy model.

Appliance (Natural Draft): Gas-fired combustion appliances installed in the living space or in an area freely communicating with the living space, vented alone or in tandem with another appliance.

Arrestance: A measure of the ability of an air filtration device to remove synthetic dust from the air.

Axial Fan: A type of ventilating fan having propeller-like blades.

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- B -

Backdrafting: Complete reversal of flow from a combustion appliance of its combustion by-products, usually due to negative pressures indoors that results in the intrusion of combustion by-products into the living space.

Balanced Ventilation: A general ventilation strategy that results in the house experiencing a neutral pressure. Neutral pressure is attained when the ventilation system is equipped to provide make-up air to compensate for the exhaust air.

Bathroom Fan: A mechanical ventilation device which, when ducted to the exterior of the house, draws out stale, impure and humid air thereby improving the quality of indoor air.

Biological Pollutants: Air pollutants, such as mold and pollen, that either are or once were alive, or by-products of metabolism.

Blower Door: A powerful fan with a flexible frame that is mounted in a buildings doorway. The device is used to pressurize or depressurize a house to evaluate its airtightness.

Blower Door Test: Professional energy auditors use blower door tests to help determine a home's airtightness. Once the airtightness of the building is evaluated steps can be taken to seal areas prone to air leakage.

British Thermal Unit (BTU): Short for British Thermal Unit, BTU is a basic measure of thermal (heat) energy. One BTU is the amount of energy needed to heat one pound of water one degree Fahrenheit, measured at its heaviest point.

Building Envelope: The exterior portion of a structure (roof, walls, and foundation), usually insulated, that surrounds the occupied space.

By-Products of Metabolism: Solids, liquids, and gases given off by living creatures as a normal part of the life process. These items can contribute to indoor air quality issues if proper ventilation is not provided.

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- C -

CADR: The Clean Air Delivery Rate indicates the volume of filtered air delivered by an air cleaner.

Canadian Standards Association (CSA): An organization that maintains standards used to certify products for safety, rate products for performance and to complement the requirements in codes.

Carbon Dioxide (CO2): A colorless, odorless gas released in exhaled breath, or by combustion processes.

Carbon Monoxide (CO): A colorless, odorless, poisonous gas released during the incomplete combustion of carbon containing fuels.

Carbon Monoxide Alarm: Every home should have at least one CO detector to alert the occupants to the presence of this colorless, odorless and harmful gas.

Carbon Dioxide Sensor: A device that senses the carbon dioxide concentration in the air and can be used to automatically control a ventilation system.

Carcinogen: A cancer causing substance.

Central Vacuum System: A type of vacuum cleaner appliance, installed into a building as a semi-permanent fixture.

Centrifugal Fan: A ventilating fan with blades resembling a squirrel cage or a hamster wheel, often used in furnaces and ventilating devices.

Chemical Sensitivity: Chemical sensitivity is a medical condition characterized by a heightened sensitivity, including allergic reactions, to chemicals.

Chimney: A vertical structure or conduit that usually carries combustion by-products out of a house. The most common reference is a chimney used to exhaust a fireplace.

Chlorofluorocarbons (CFCs): Chlorofluorocarbons define a category of chemicals which contain chlorine, fluorine and carbon. These chemicals are known to deplete the Earth's ozone layer.

Combustion Air: Air that enters a house specifically to be used in the combustion of a fuel.

Combustion Pollutants: Gases and particulates released during the burning of a fuel.

Combustion Gases: Gases released during the combustion of heating and other fuels that can include carbon monoxide, sulfur dioxide, and nitrogen dioxide.

Combustion Air Duct: A duct through which combustion air travels from the outdoors to a combustion device.

Condensation: The changing of a gas or vapor into a liquid, accompanied by the release of heat.

Conditioned Space: The part of a house, within the building envelope, that is kept at a comfortable controlled temperature and humidity levels. Building scientists and Building America research indicate that placing ducts inside the home's conditioned space can significantly reduce energy loads and utility bills.

Controlled Pressure: An airpressure difference between the indoors and the outdoors, purposefully induced by ventilation equipment. This is typically achieved with supply-only or exhaust-only ventilation products.

Controlled Ventilation: Purposeful air movement into and out of a building.

Convective Air Currents: The movement of air resulting from heat transference through the air by convection.

Cubic Feet Per Minute (CFM): Short for cubic feet per minute CFM is a measure of the volume of air that flows into or out of a space.

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- D -

Damper: A device, often motorized or manually adjustable, used to vary or control the airflow in a duct.

Dander: Another word for dandruff, it is used most often to describe pet skin particles and adhering body fluids such as saliva that end up in our homes.

Decibel (dB): A logarithmic unit of measurement used to express sound intensity. A difference of ten decibels is 10 times as loud as a difference of 1 decibel.

Defrost Mechanism: A device used in heat or energy recovery ventilators to melt any ice that builds up in the core in cold climates during below freezing temperature conditions.

Degree Day: A unit of measurement used to estimate fuel consumption and heating or cooling costs, based on temperature and time.

Dehumidistat: A moisture control device that can be used to activate a ventilation system or dehumidifier when the relative humidity rises.

Deliberate Holes: Openings (inlets or outlets) that are purposely placed in a house through which air can enter or leave.

Demand-Controlled Ventilation: The process of automatically supplying air to, and removing air from, a house whenever needed by the occupants.

Depressurization: When the air pressure inside a house or room is less than the atmospheric pressure outside the house or room.

Dew Point: The temperature at which air is saturated with moisture, (100% relative humidity), below which condensation will occur.

Dilution: The mixing of fresh air into stale air to reduce the concentration of pollutants. The recommended rates are typically given as (ACH), air changes per hour or (ACR) air change rate.

Displacement Ventilation: A method of very effectively moving air through a room, generally only used in specialized applications.

Downdraft: A term often applied to kitchen exhaust fans that pull air across the cooking surface.

Drying Potential: The ability of a substance to dry out after it becomes wet.

Duct: A conduit for supplying or exhausting air that can be made from a variety of materials and in a variety of shapes.

Ductboard: A semi-rigid fiberglass material with an aluminum foil facing on one side used to construct ducts.

Dust Mites: Dust mites are microscopic bugs that live in household dust. They work their way into soft places like pillows, blankets, mattresses, and stuffed animals and can cause allergies and other respiratory problems.

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- E -

Effective Leakage Area: Effective Leakage Area (ELA) was developed by Lawrence Berkeley Laboratory (LBL) and is used in their infiltration model. The Effective Leakage Area is defined as the area of a special nozzle-shaped hole (similar to the inlet of your blower door fan) that would leak the same amount of air as the building does at a pressure of 4 Pascals.

Electrically-Commutated Motor: Synchronous motors that are powered by a DC electric source via an integrated inverter/switching power supply, which produces an AC electric signal to drive the motor.

Electrostatic Air Filter: An air filter composed of plastic materials that captures particulate pollutants using static electricity.

Energy Recovery Ventilator (ERV): A mechanically powered ventilating device with separate intake and exhaust air streams, and a heat exchanger to transfer a portion of the total energy (heat and moisture) from one air stream to the other.

Enthalpy: The total amount of heat contained in air: the sum of the sensible heat and the latent heat.

Equivalent Leakage Area: The Equivalent Leakage Area (EqLA) is defined by Canadian researchers at the Canadian National Research Council as the area of a sharp edged orifice (a sharp round hole cut in a thin plate) that would leak the same amount of air as the building does at a pressure of 10 Pascals.

Equivalent Length: The length of straight duct that would have the same resistance to airflow as a fitting.

Exchange Rate: The rate at which indoor air is replaced with outdoor air.

Exfiltration: Air leaving a house through random holes in the structure.

Exhaust Air: Bathroom exhaust fans, clothes dryers, built-in vacuum cleaners, dust collection systems, and range hoods all exhaust air from a building.

Exhaust Air Transfer (EAT): The percent of exhaust air found in the supply airstream at the specified external total static pressure. Gross Airflow x (1-(EAT/100)) = Net Airflow.

Exhaust Ventilation: A general ventilation strategy that uses an exhaust fan to remove air from a house. An equal volume of make-up air enters either by way of through-the-wall vents, through a fresh-air duct connected to a forced-air heating/cooling system, or through random holes in the structure of the house.

Exhaust-Only Ventilation: A ventilation strategy that uses one or more fans to exhaust stale air that is replaced by outdoor air entering through passive inlets and/or random leaks. See central exhaust ventilation.

External Static Pressure: The total static pressure loss of the exhaust or supply system in the ductwork. In the case of the exhaust system, the total static pressure differential is the static pressure measured at (.4) minus the static pressure measured at (.3). The supply system total static pressure differential is the static pressure measured at (.2), minus the static pressure measured at (.1).

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- F -

Filtration: The process of removing particulates or pollutants from air.

Formaldehyde: Formaldehyde is a colorless, flammable gas at room temperature and has a strong odor. Exposure to formaldehyde may cause adverse health effects.

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- G -

Gross Airflow: The measured airflow rate at (.2) and (.3), which may contain cross-leakage between the supply and exhaust airstreams. These values are used for duct design.

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- H -

Heat Pump Water Heaters: A heat pump also can be used to heat water either as a stand-alone water heating system, or as a combination water heating and space conditioning system.

Heat-Recovery Ventilator (HRV): A mechanically powered ventilating device with separate intake and exhaust air streams, and a heat exchanger to transfer a portion of the sensible energy (heat) from one airstream to the other.

Heating Season Performance: This is a mandatory test for HVI Certification at 0°C (+32°F) and 75% relative humidity for the outdoor air and at 22°C (71.6°F) and 40% relative humidity for the indoor air. This test represents the typical steady-state energy performance of the HRV/ERV. Performance is more comparable using this Heating Season Performance data due to the absence of frost formation.

HEPA Filter: Stands for High Efficiency Particulate Air filter.

HERS: The Home Energy Rating System (HERS) Index is the industry standard by which a home's energy efficiency is measured

Home Ventilating Institute (HVI): Founded in 1955, HVI certifies a wide range of home ventilating products manufactured by companies located throughout the world which produce the vast majority of the residential ventilation products sold in North America.

Humidifier: A device for adding moisture to interior conditioned spaces.

Humidistat: A control device that can be used to activate a ventilation system as the relative humidity falls.

Humidity: Humidity is moisture in the air in the form of invisible water vapor. See absolute humidity and relative humidity.

HVAC: A common term used to reference a buildings heating, ventilating and air conditioning system.

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- I -

In-Line Fan: A fan designed to be located within the building structure with ductwork on both the intake and exhaust ends of the fan.

Inches Water Gauge: A unit of pressure measurement. About 250 Pa. equals 1" w.g.

Infiltration: The unintentional or accidental introduction of outside air into a building typically through cracks in the building envelope and through use of doors for passage. Infiltration is sometimes called air leakage.

Infrared Thermography: Thermographic inspection measures surface temperatures by using infrared video and still cameras. These tools see infrared light (light that is in the heat spectrum) to detect temperature variations of the building's "skin" showing warmer areas in lighter colors and cooler areas in darker colors.

Insulation: A material that inhibits the flow of heat. Materials commonly used for insulation include foam board, fiberglass batts and blown cellulose.

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- J -

Jump Duct: A short duct connecting two rooms through which air can move when pressure imbalances occur between the rooms.

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- K -

Kilowatt Hour (kWh): A unit of measuring electrical energy equal to 1,000 watts of power consumed over an hour.

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- L -

Latent Recovery/Moisture Transfer (LRMT): Moisture recovered divided by moisture exhausted and corrected for the effects of cross-leakage. LRMT = 0 indicates that moisture was not transferred (net of cross-leakage) from the exhaust airstream to the supply airstream. LRMT = 1 would indicate complete transfer of moisture. LRMT is provided for the Heating Season Performance and the Very Low Temperature Test as an indication of moisture handling characteristics, and may be used to evaluate the moisture transferability of the equipment in order to assess the humidification or dehumidification performance of the product at the specified test condition.

LEED: Leadership in Energy and Environmental Design is a green building certification program that recognizes best-in-class building strategies and practices.

Liters per second (l/s): A metric unit of measurement used to rate a fan's capacity. One liter per second is equal to approximately 2 cubic feet per minute. Since cfm is how HVI measures airflow, the link will provide a conversion chart.

Local-Exhaust Ventilation: The quick removal of air pollutants from near the source to the outdoors.

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- M -

Make-Up Air: Outdoor air that enters a house to replace air that is exhausted from the house.

Mechanical Ventilation: The process of supplying air to, and removing air from, a house.

MERV: Stands for Minimum Efficiency Reporting Value. This is a rating system noting an air filter's efficiency at removing different size particulates from a stream of air.

Mold: An organic growth which can occur indoors when mold spores land on surfaces that are wet.

Multi-Port Ventilator: An exhaust device having several suction connections for running ducts from different rooms.

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- N -

Natural Draft: Unforced gas flow through a chimney or vertical duct, directly related to chimney height and the temperature difference between the ascending gases and the atmosphere, and not dependent upon the use of fans or other mechanical devices.

Natural Pressure: An air pressure difference between the indoors and the outdoors induced by natural phenomena such as wind, stack effect, and diffusion.

Natural Ventilation: An uncontrolled air movement from windows, doors, or cracks in the home.

Negative Pressure: When the air pressure inside a house or room is less than the atmospheric pressure outside the house or room.

Net Supply Airflow: The gross supply airflow reduced by measured cross-leakage (EAT). This is the actual amount of outdoor air delivered by the supply system of the unit and is used for sizing the equipment for the required ventilation rate.

Neutral Pressure: Air pressure inside a house that is equal to the atmospheric pressure outside the house.

Neutral-Pressure Plane: That part of a house that experiences neutral pressure as a result of stack effect or as a result of combined pressures.

Nontoxic: Implies that a substance will not cause adverse health effects.

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- O -

Occupied Space: The part of a house to which the occupants normally have access; habitable rooms. Also called the living space.

Outgassing: The release of volatile gases from a solid material as a part of aging, decomposition, or curing.

Ozone: A form of Oxygen, O3, that is found in a layer high in the earth’s atmosphere. It absorbs the ultraviolet component of incoming solar radiation that can be harmful to life on earth.

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- P -

Particulate Filter: An air filter designed to remove particulates from the air.

Particulates: Solid (or liquid) air pollutants, as opposed to gases.

Parts per Million (ppm): A small unit of measurement often used to express the concentration of pollutants in the air.

Pascal: The pascal (Pa) or kilopascal (kPa) is a unit of pressure measurement. One pound per square inch (psi) equals about 7,000 Pascals.

Passive Ventilation: Caused by house pressurization or depressurization not directly caused by a fan. Infiltration and exfiltration involve passive air movement.

Picocurie per liter (pC/l): A unit of measurement used to determine the concentration of radon in the air.

Positive Pressure: When the air pressure inside a house or room is greater than the atmospheric pressure outside the house or room.

Pressurization: When the air pressure inside a house or room is greater than the atmospheric pressure outside the house or room.

Psychometric Chart: A graph used to determine the moisture content and energy of air at different temperatures.

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- R -

Radon: A naturally occurring radioactive gas often released from soil and rocks.

Radon Daughters: The natural radioactive decay products of radon some of which release harmful radiation.

Radon Progeny: The natural radioactive decay products of radon some of which release harmful radiation. Formerly known as radon daughters.

Recirculate: To move air through the living space without adding fresh air or removing stale air.

Recirculating Range Hood: A ductless range hood that is not connected to the outdoors.

Relative Humidity (RH): The amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.

Return Air: Air from a living space that enters an air handler, such as a furnace or air conditioner, and is returned back to the space.

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- S -

Sealed Combustion: A system in some furnaces, boilers, fireplaces, and water heaters that is immune to pressure imbalances in a house because it draws combustion air from the outdoors into a sealed chamber and expels by-products to the outdoors.

SEER: Seasonal Energy Efficiency Ratio (SEER). This is an efficiency rating system used for central air conditioning systems.

Sensible Heat: The amount of heat involved in raising or lowering the temperature of air not including any heat required to cause water vapor to change state (e.g. from a gas to a liquid).

Sensible Recovery Efficiency (SRE): The net sensible energy recovered by the supply airstream as adjusted by electric consumption, case heat loss or heat gain, air leakage, airflow mass imbalance between the two airstreams and the energy used for defrost (when running the Very Low Temperature Test), as a percent of the potential sensible energy that could be recovered plus the exhaust fan energy. This value is used to predict and compare Heating Season Performance of the HRV/ERV unit.

Sick Building Syndrome: The term "sick building syndrome" (SBS) is used to describe situations in which building occupants experience acute health and comfort effects but no specific illness or cause can be identified.

Sone: The sone is an internationally recognized unit of loudness which simplifies reporting of sound output. The sones translate laboratory decibel readings into numbers that correspond to the way people sense loudness. Sones follow a "linear" scale like inches. Double the sone is double the loudness. In contrast decibels follow a "logarithmic" scale which stands for a complete multiplying of numbers instead of simple adding. Sone readings offer easy, quick and accurate comparisons for both laymen and engineers. In technical terms, the sone is equal in loudness to a pure tone of 1,000 cycles per second at 40 decibels above the listener’s threshold of hearing. In everyday terms, one sone is equivalent to the sound of a quiet refrigerator in a quiet kitchen.

Sone Rating: Sone ratings permit easy and accurate comparisons of exhaust fans tested under identical laboratory standards and conditions. A fan rated at 3 Sones makes half the sound of one of 6 Sones, just as 100 CFM is half the air movement of 200 CFM.

Sound Attenuator: A device similar to an automotive muffler that can be used to absorb some of the sound generated in a ventilation system.

Source Control: The practicing of placing localized ventilation products to quickly extract pollutants from the source as they are generated.

Specific Humidity: This is a ratio of the water vapor content of the mixture to the total air content on a mass basis.

Spillage: A situation where some of the combustion by-products spill into the living space rather than go up the chimney, usually due to insufficient draft.

Spot Ventilation: Ventilation for the quick removal of air pollutants from near a source. See also local-exhaust ventilation.

Stack Effect: The naturally occurring phenomena of warm air exerting pressure on cooler air that results in warm air rising.

Stale Air: The air leaving a house through a ventilation system.

Static Pressure: The amount of pressure exerted against the walls of a duct or airway created by the friction and impact of air as it moves.

Static Pressure Drop: The change in pressure resulting from resistance to airflow.

Supply Air: The air entering a house through a ventilation system. Also, the conditioned air passing through a furnace or air conditioner into the living space.

Supply Grille: A grille through which fresh air enters a room.

Supply Ventilation: A general ventilation strategy that uses either a supply ventilation fan or a forced-air heating/cooling fan to draw air into a house.

Supply-Only Ventilation: A general ventilation strategy that uses either a supply ventilation fan or a forced-air heating/cooling fan to draw air into a house.

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- T -

Thermographic Inspection: Thermographic inspection measures surface temperatures using infrared light, (light that is in the heat spectrum), to detect temperature variations of the building's "skin" showing warmer areas in lighter colors and cooler areas in darker colors.

Total Recovery Efficiency (TRE): The net total energy, (sensible plus latent, also called enthalpy), recovered by the supply airstream adjusted by electric consumption, case heat loss or heat gain, air leakage and airflow mass imbalance between the two airstreams, as a percent of the potential total energy that could be recovered plus the exhaust fan energy. This value is used to predict and compare Cooling Season Performance for the HRV/ERV unit.

Transfer Duct: A short duct connecting two rooms through which air can move when pressure imbalances occur between the rooms. Also known as a jump duct.

Transfer Grille: An opening between two rooms through which air can move when pressure imbalances occur between the rooms.

TSCA: The Toxic Substances Control Act (TSCA) requires EPA to compile, keep current, and publish a list of each chemical substance that is manufactured or processed in the United States.

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- U -

United States Environmental Protection Agency (USEPA): A federal agency charged with monitoring and regulating environmental quality, including air quality, and providing research-based information to the public.

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- V -

Vapor: The gaseous form of a substance that is normally a liquid at room temperature.

Vapor Barrier: A man made material, often a plastic or foil sheet used in building construction that prevents the migration of water vapor from the outside to the inside of a structure.

Vapor Pressure: A force that drives vapor molecules from an area of high concentration to an area of low concentration. In homes this typically refers to water vapor pressure.

Ventilation: The process of supplying air to, or removing air from, a house.

Very Low Temperature Ventilation Reduction (VLTVR): The percent reduction in airflow rate of the supply and exhaust systems at the end of the 72-hour test compared with operation under non-frosting conditions. The final airflow rate is taken as the average of the last 60 hours of the test. This reduction in airflow results from frost and ice buildup in the exchanger and variation in mechanical ventilation during defrosting.

Very Low Temperature Airflow Imbalance (VLTAI): The percent of airflow imbalance of the Supply System Airflow compared to Exhaust System Airflow over the last 60 hours of the 72-hour test.

Volatile Organic Compound (VOC): A class of hundreds of different molecular compounds containing carbon that easily evaporates, often released from building materials and found as contaminants in indoor air.

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- W -

Whole-House Fan: Whole-house ventilation is intended to dilute the indoor air with fresh outdoor air, thereby diluting the pollutants in the air. Whole-house ventilation usually runs constantly. If it is designed to run intermittently, it must be automatically controlled and have a higher flow rate than if it ran continuously. Whole-house ventilation may be provided with exhaust, supply, or balanced ventilation.

Whole House Comfort Ventilator: Whole house comfort ventilators allow the house to breathe freely when summer breezes are not strong enough to cool the house. A properly located whole house comfort ventilator draws cooler outside air through screened windows and doors, pulls it up through the house and exhausts it, usually through static vents in the attic.

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