Common HVAC Terms – Dictionary
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 during your buying decision.
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
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.
Airflow 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.
AHRI: Air Conditioning, Heating 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.
BTU/h: 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 outdoors 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.
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
Down flow 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 airflow.
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
NATE: North American Technician Excellence
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
Up flow 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.
Variable Speed Blower Motor: A motor that is able to run at capacities between 20% and 100% based on pre-programmed algorithms in the circuit board of the furnace. This blower motor converts A/C current to D/C current that enables the blower motor to run at a lower cost to operate. The benefits of a variable speed blower motor are, 1/3 of the cost to operate the fan, quieter operation, fan ramps up and down slowly, continuous air supply into the home at lower speeds.
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.