A
AC Alternating Current - A type of current where the polarity is perpetually
reversing, causing the directional flow in a circuit to reverse at regular
intervals.
ACCA - Air Conditioning Contractors of America.
Acoustical - Relating to sound, the science of sound, or a sense of hearing.
AFUE - Annual Fuel Utilization Efficiency. A measurement used to rate furnace
efficiencies by dividing the ratio of heat output by heat input.
AGA - American Gas Association, Inc.
Air Conditioner - A device that changes humidity levels, temperature or quality of
air.
Air Flow Volume - Measured in cubic feet per minute (cfm), this is the amount of air
circulated in a space.
Air Handler - Parts of a system including the fan-blower, filter and housing.
ARI - Air Conditioning and Refrigeration Institute.
ASHRAE - American Society of Heating, Refrigeration and Air Conditioning
Engineers.
B
BTU - British Thermal Unit. Measures the amount of heat required to raise or
lower the temperature of one pound of water one degree Fahrenheit.
BTUh - British Thermal Units per hour.
Burner - The device that facilitates the combustion of air and gas.
Burner Orifice - The opening in the burner through which the gas or fuel passes
prior to combustion.
C
Capacity - HVAC capacity is the output produced by the heating or cooling unit and
is measured in BTUs per hour.
Celsius - A temperature scale that registers the freezing point of water as 0° and
the boiling point as 100° under normal atmospheric pressure.
CFM - Cubic Feet per Minute. A measurement of airflow volume.
Charging a System - Adding coolant, or refrigerant, to an HVAC system.
Compressor - A pump that increases the pressure of gas.
Condensate - Vapor that is turned into a liquid as its temperature is lowered.
Condenser Coil - Also an outdoor coil. A device that removes heat from the
refrigerant, allowing the refrigerant to be converted from vapor to liquid.
Condenser Fan - A fan that passes air over the condenser coil to facilitate the
removal of heat from the refrigerant.
CSA - Canadian Standards Association.
D
DC - Direct Current. A type of electrical current that only flows in one direction.
Damper - Found at the exit point of ductwork, this plate usually contains grates
that can be opened or closed to control the flow of air into a zone.
Degree-Day - Calculated by subtracting the average outdoor temperature for an
area from 65º Fahrenheit. This measurement is used to estimate the amount of
heating or cooling a home or building will need.
Dehumidifier - A device that removes humidity, or moisture, from the air.
Diffuser - A grille over an air supply duct with vanes that distribute the
discharging air in a specific pattern or direction.
DOE - Department of Energy.
Downflow Furnace - A furnace with an intake on the top and an air discharge at
the bottom.
Drain Pan - Also a condensate pan. As the refrigerant vapor is liquefied, the drain
pan collects the condensate and funnels it to the drain line.
Dry Bulb Temperature - The temperature as measured without the consideration of
humidity.
Ductwork - A network of metal, fiberboard or flexible material flowing
throughout a space which delivers air from an HVAC unit to the respective zones
of a home or office.
E
EER - Energy Efficiency Ratio.
EPA - Environmental Protection Agency.
Expansion Valve - A valve that meters the levels of refrigerant through a
temperature or pressure control.
Evaporator Coil - Also an indoor coil. A device that is designed to absorb heat in
the air in order to change the liquid refrigerant that flows through it into a
vapor.
F
Fahrenheit - A temperature scale in which water freezes at 32 degrees and boils
at 212 degrees at normal atmospheric pressure.
Fan - A device that creates air flow.
Filter - A device that acts like a strainer to remove dirt or undesired particles.
Flue - A vent that removes the byproducts of combustion from a furnace.
Furnace - The major component in heating a home. A device that facilitates the
combustion of fuel and air to create heat.
Fuse - A delicate metal strip connecting two parts of an electrical circuit. This
strip breaks, or melts, in the event of excess electrical charge, breaking the
electrical circuit.
G
GAMA - Gas Appliance Manufacturers Association.
H
Heat Exchanger - A device through which heat is transferred to a cold area or
surface.
Heat Gain - The amount of heat added or created in a designated area.
Heating Coil - A coil that acts as a heat source for a heating system.
Heat Loss - The amount of heat subtracted from a designated area.
Heat Pump - A device used for either the heating or cooling of a space by
transferring heat between two reservoirs.
Heat Transfer - Moving heat from one location to another.
HSPF - Heating Seasonal Performance Factor. This factor rates the efficiency of
the heating portion of the heat pump.
Humidifier - A device that adds humidity, or moisture, to the air.
Humidistat - The device that measures humidity and turns the humidifier on and off.
Humidity - Dampness in the air caused by water vapor.
HVAC - Heating, Ventilation and Air Conditioning.
I
Ignition - Elevating the temperature of a substance to the point of causing a
combustion reaction.
K
Kilowatt (kW) - 1,000 watts.
L
Latent Heat - A type of heat that when added to an area produces an effect other
than an increase in temperature.
M
Media - The fine material of a filter that traps dirt, dust, mildew or bacteria.
N
NEC - National Energy Council / National Electric Code.
NEMA - National Electrical Manufacturing Association.
O
Orifice - An opening or hole.
P
Package Unit - A heating and cooling system contained in one outdoor unit.
PSI - Pounds per square inch.
PSIA - Pounds per square inch, absolute.
PSIG - Pounds per square inch gauge.
PVC - Polyvinyl chloride; a type of plastic.
R
Reciprocating Compressor - A type of compressor used in cooling systems to
compress refrigerant by using a piston action.
Refrigerant - A chemical that condenses from a vapor to liquid and, in the process,
decreases in temperature.
Refrigerant Charge - The amount of refrigerant in a system.
S
SEER - Seasonal Energy Efficiency Ratio. A rating system developed by the U.S.
Government to indicate the efficiency level of cooling equipment.
Self-contained System - A package unit.
Sensible Heat - Heat added or subtracted that causes a change in temperature.
Sensor - A device that reacts to a change in conditions.
Split System - An outdoor unit combined with an indoor unit.
T
Thermostat - Sensors that monitor and control the output of an HVAC system.
Thermostatic Expansion Valve - A device that creates a constant evaporator
temperature.
Ton - One ton is 12,000 BTUs per hour.
U
Upflow Furnace - A furnace that pulls in air from the bottom and releases it
through the top.
V
Vacuum - A space where the pressure is significantly below that of standard
atmospheric pressure.
Volt - A unit of electro-motive force.
Voltage - The force pushing electrical current along wires and cables.
W
Watt - The unit of electrical power equal to the flow of one amp at a potential
difference of one volt.
Wet Bulb Thermometer - A thermometer that measures the relative humidity in the
air.
Z
Zoning - A system that divides a home, office or space into different regions in
order to better control the temperature and effectiveness of a heating and
cooling system.