The HVAC industry can be a maze of unfamiliar
acronyms and industry terms. This dictionary will help you
navigate the most common terms you’ll come across in residential
Heating and Cooling.
C D E
F G H
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P R S
T U V
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
exchanger consisting of two diagonal coils that are joined
together and looks like the letter "A".
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 Balance Test -
A test used to measure airflow across a tower or air
Air Balancing Hood -
Measures airflow from grilles and diffusers.
Air Conditioner - A device that changes
humidity levels, temperature or quality of air.
Air Flow Volume
The amount of air the system circulates through your home,
expressed in cubic feet per minute (cfm). Proper air flow
depends on the outdoor unit, the indoor unit, the ductwork and
even whether the filters are clean.
Air Handler - Parts of a system including
the fan-blower, filter and housing.
portion of the central air conditioning or heat pump system that
moves heated or cooled air throughout a home’s ductwork. In some
systems a furnace handles this function.
Amp (Ampere) -
The practical meter-kilogram-second unit of electric current
that is equivalent to a flow of one coulomb per second or to the
steady current produced by one volt applied across a resistance
of one ohm.
ARI - Air Conditioning and Refrigeration
ASHRAE - American Society of Heating,
Refrigeration and Air Conditioning Engineers.
Bearing - A
support or guide by means of which a moving part such as a shaft
or axle is positioned with respect to the other parts of a
Biocide - A
substance that is destructive to many different organisms.
Thermal Unit. Used for both heating and cooling, BTU is a
measure of the heat given off when fuel is combusted. Or for
cooling, it’s a measure of heat extracted from your home. One
BTU is equal to the heat given off by a wooden kitchen match.
BTU also measures the amount of heat required to raise or lower
the temperature of one pound of water 1o
Thermal Units per hour. 12,000 BTUh equals one ton of cooling.
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.
Capacity - HVAC capacity is the output
produced by the heating or cooling unit and is measured in BTUs
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.
Coil Cleaning - The act
of removing or cleaning dirt, dust, grime, hair and oils from
either an indoor or outdoor evaporator or condenser coil.
Compressor - A pump that increases the
pressure of gas. The motor in the compressor is the main
consumer of energy. If the compressor operates out of its
original design, it will effect energy consumption.
Condensate - Vapor that is turned into a
liquid as its temperature is lowered.
Condenser - Also called
a condensing unit - Heat exchanger where the system
heat is rejected and the refrigerant condenses into a liquid.
(This is the equipment most often called the "air Conditioner"
usually located on the ground or rooftop outside a home or
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
Contactor - A switch
that can repeatedly cycle, making and breaking an electrical
circuit. When sufficient current flows through the A-coil built
into the contactor, the resulting magnetic field causes the
contacts to be pulled in or closed.
CSA - Canadian Standards Association.
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.
EER - Energy Efficiency Ratio.
Electronic Air Cleaner (EAC) -
An electronic device that filters out large
particles and contaminants in indoor air. It then electronically
pulls out tiny particles that have been magnetized, such as
viruses and bacteria, drawing them to a collector plate.
EPA - Environmental Protection Agency.
Expansion Valve - A valve that meters the
levels of refrigerant through a temperature or pressure control.
Part of a air conditioner or heat pump. The evaporator coil
cools and dehumidifies the air by converting liquid refrigerant
into a gas, which absorbs the heat from the air. The warmed
refrigerant is then carried through a tube to the outdoor unit
Fahrenheit - A temperature scale in which
water freezes at 32 degrees and boils at 212 degrees at normal
Fan - A device that creates air flow.
Fan Coil - An indoor
component of a heat pump system, used in place of a furnace, to
provide additional heating on cold days when the heat pump does
not provide adequate heating.
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
GAMA - Gas Appliance Manufacturers
Heat Exchanger - A device through which heat
is transferred to a cold area or surface.
the furnace, the heat exchanger transfers heat to the
surrounding air, which is then pumped throughout the home.
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.
Load - A series of studies performed to determine the
heating or cooling requirements of your home. An energy load
analysis uses information such as the cubic footage, window and
door areas, insulation quality and local climate to determine
the heating and cooling capacity needed by your furnace, or air
conditioner. When referring to heating, this is also called Heat
Loss Analysis, since a home’s heating requirements are
determined by the amount of heat lost through the roof, entry
ways and walls.
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
Heat Transfer - Moving heat from one
location to another.
High Efficiency Air
- An air
filter installed in your central system that collects up to 99%
of particles 5 microns or larger. In comparison your standard
air filter only picks up about 8% of these same particles.
- A type of furnace, installed on its "side," that draws in air
from one side, heats it and sends the warm air out the other
side. Most often used for installations in attics or crawl
HSPF - Heating Seasonal Performance Factor.
This factor rates the efficiency of the heating portion of the
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
HVAC - Heating, Ventilation and Air
Ignition - Elevating the temperature of a
substance to the point of causing a combustion reaction.
Indoor Coil -
coil), part of a split-system air conditioner or heat pump
located indoors. The evaporator coil cools and dehumidifies the
air by converting liquid refrigerant into a gas, which absorbs
the heat from the air. The warmed refrigerant is then carried
through a tube to the outdoor unit (condenser coil).
Kilowatt (kW) - 1,000 watts.
Latent Heat - A type of heat that when added
to an area produces an effect other than an increase in
- Also heat load. A
series of studies performed to determine the heating or cooling
requirements of your home. An energy load analysis uses
information such as the square footage, window and door areas,
insulation quality and local climate to determine the heating
and cooling capacity needed by your furnace, or air conditioner.
When referring to heating, this is also called Heat Loss
Analysis, since a home’s heating requirements are determined by
the amount of heat lost through the roof, entry ways and walls.
- A heating and cooling
system comprised of products that have been certified to perform
at promised comfort and efficiency levels when used together,
and used according to design and engineering specifications.
Media - The fine material of a filter that
traps dirt, dust, mildew or bacteria.
NEC - National Energy Council / National
NEMA - National Electrical Manufacturing
- The day-to-day cost to
run your home comfort system, based on the energy required to
Orifice - An opening or hole.
Unit - The
portion of a heat pump or central air conditioning system that
is located outside the home and functions as a heat transfer
point for collecting heat from and dispelling heat to the
Package Unit - A heating and cooling system
contained in one outdoor unit.
Overall measure of the efficiency and value of your home comfort
system. By combining your purchase price and ongoing operating
costs, a payback analysis determines the number of years
required before monthly energy savings offset the purchase
- An electronic
thermostat with a built in memory that can be programmed for the
different temperature settings at different times of day.
PSI - Pounds per square inch.
PSIA - Pounds per square inch, absolute.
PSIG - Pounds per square inch gauge.
- Puron is a trade marked
name for R-410A, an environmentally sound refrigerant designed
to protect the earth's ozone layer. Federal law requires all
manufacturers phase out ozone depleting refrigerants in the next
few years. Puron is approved by the US Environmental Protection
Agency as a replacement from Freon 22*.
PVC - Polyvinyl chloride; a type of plastic.
Chlorodifluoromethane or difluoromonochloromethane is a
refrigerant commonly used in air conditioning applications, such
as residential split systems in the US, rooftop units and window
R-410A - Sometimes sold
under the trademarked names Puron, Genetron R410A, and AZ-20, is
pentafluoroethane which is used
as a refrigerant in air conditioning applications. Unlike many
haloalkane refrigerants it does
not contribute to ozone depletion, and is therefore becoming
more widely used as ozone-depleting refrigerants like R-22 are
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.
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
Split System - An outdoor unit combined with
an indoor unit.
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.
Upflow Furnace - A furnace that pulls in air
from the bottom and releases it through the top.
Vacuum - A space where the pressure is
significantly below that of standard atmospheric pressure.
Variable Speed -
A "smart" motor that runs on DC current and can vary
it's operating speed using less electricity and providing
Volt - A unit of electro-motive force.
Voltage - The force pushing electrical
current along wires and cables.
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.
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