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DamperA device, often motorized or manually adjustable, used to vary or control the airflow in a duct.
DanderAnother 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.
DeckThey need a physical exam yearly, just like you do.
Defrost MechanismA 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 DayA unit of measurement used to estimate fuel consumption and heating or cooling costs, based on temperature and time.
Dehumidifying Heat PipeIn humid climates, even air conditioned air may feel clammy without the assistance of a little technology.
DehumidistatA control device that can be used to activate a ventilation system when the relative humidity rises.
Deliberate HolesOpenings (inlets or outlets) that are purposely placed in a house through which air can enter or leave.
Demand-Controlled Ventilation (DCV)The process of automatically supplying air to, and removing air from, a house whenever needed by the occupants.
DepressurizationWhen the air pressure inside a house or room is less than the atmospheric pressure outside the house or room.
DesiccantA substance that absorbs moisture, used in some energy recovery ventilators to enhance moisture transfer between airstreams.
DesuperheaterDesuperheaters work in tandem with geothermal heat pumps to heat water.
Dew PointThe temperature at which air is saturated with moisture (100% relative humidity), below which condensation will occur.
Di-octyl Phthalate (DOP)An inert gas used to test high-efficiency (HEPA) particulate air filters.
DiffuserA grille designed to direct airflow in a specific pattern into a room for proper distribution.
DiffusionThe migration of molecules of a gas or a vapor (or a liquid) from an area of high concentration to an area of low concentration.
Diffusion BarrierA material that slows down the amount of diffusion through a solid material, often used in insulated walls.
Diffusion RetarderA material that slows down the amount of diffusion through a solid material, often used in insulated walls.
DilutionThe mixing of fresh air into stale air to reduce the concentration of pollutants; also applies to liquids.
Dilution AirAir that mixes with combustion by-products prior to their being expelled from a house through a natural-draft chimney.
Displacement VentilationA method of very effectively moving air through a room, generally only used in specialized applications.
DOP-Smoke-Penetration TestA method of testing high-efficiency (HEPA) air filters.
Double-Flow VentilationA general ventilation strategy that results in the house experiencing a neutral pressure.
DowndraftA term often applied to kitchen exhaust fans that pull air downward.
DraftA breeze or current of air in a room, often uncomfortable.
Drying PotentialThe ability of a substance to dry out after it becomes wet.
DuctA conduit for moving air, made from a variety of materials and in a variety of shapes.
DuctboardA semi-rigid fiberglass material with an aluminum-foil facing on one side, used to construct ducts.
Dust MitesThese tiny creatures can cause allergies and other respiratory problems.
Dynamic WallAn insulated part of a house’s structure through which outdoor air can pass from the outdoors to the indoors and is tempered in the process.

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