Glossary of HVAC Terms: Comprehensive Guide to HVAC Terminology

Welcome to our comprehensive Glossary of HVAC Terms! Whether you’re an HVAC professional or a homeowner seeking to better understand your HVAC system, this glossary provides clear and concise definitions for various HVAC terms.

From basic concepts to advanced technical jargon, you’ll find everything you need to confidently navigate the world of HVAC. Explore the terms below to enhance your knowledge and ensure your HVAC system operates efficiently and effectively.

A

• A2L Refrigerant Class (Safety Classification): A group of newer low-GWP refrigerants, including R-32 and R-454B, with low toxicity and mild flammability. Requires updated Canadian codes for safe use.
• Absolute Pressure: The combined pressure within a system, accounting for both gauge and atmospheric pressure: Often noted with an “a” (e.g., BARa for bar absolute, PSIa for pounds per square inch absolute).
• Accumulator: A storage tank in a refrigeration system that holds liquid refrigerant from the evaporator, preventing it from returning to the compressor and causing potential damage.
• AC Fans: Fans driven by alternating current (AC) motors, used to move air in heating, cooling, and ventilation systems.
• Air Changes Per Hour (ACH): A metric indicating how often the air within a space is replaced with ventilation air per hour.
• ACRIB: Air Conditioning and Refrigeration Industry Board: An organization advocating for the air conditioning and refrigeration sector, offering guidance, regulation, and standards.
• Advanced Reciprocating Compressor: An enhanced type of compressor designed for more efficient refrigerant compression.
• Adiabatic Cooling: A cooling process that decreases temperature by changing air pressure through volume expansion, without heat loss or gain in the system.
• AHRI (Equipment Certification for Canada): Though U.S.-based, AHRI certifies HVACR equipment used in Canada under NRCan rules, ensuring units meet efficiency standards without extra testing.
• Air Conditioner: A device that manages the temperature, humidity, and air quality within a specified area.
• Air-cooled System: An air conditioning system that uses air to dissipate heat from the refrigerant in the condenser, typically with the condenser located outside to release heat into the atmosphere.
• Air Diffuser: A device that directs airflow within a space, ensuring balanced air distribution.
• Air Flow Distribution: The manner in which air is circulated through a space by an HVAC system.
• Air Handling Unit (AHU): A central unit in HVAC systems that includes fans, heating and cooling elements, filter racks, dampers, humidifiers, and other equipment necessary for ventilation and air extraction.
• Air Purifier: A device used to clean the air within HVAC systems.
• AHRI: Air Conditioning, Heating, and Refrigeration Institute: A US-based association that standardizes testing and certification of HVAC equipment to ensure performance meets specified criteria.
• Alternating Current (AC): An electrical current type where the flow of electric charge periodically reverses direction, used in HVAC systems to power equipment like fans, compressors, and pumps.
• Ambient: Refers to the surrounding environmental conditions of temperature and pressure.
• Amps (Amperage): A unit measuring the strength of an electrical current.
• Annual Fuel Utilization Efficiency (AFUE): A metric that measures the efficiency of a furnace or boiler in converting fuel to heat over a typical year.
• Application: The specific site or location where an air conditioning or cooling system is to be installed or used.
• ASHRAE: American Society of Heating, Refrigerating, and Air-Conditioning Engineers: A global organization dedicated to advancing human well-being through sustainable technology for the built environment.
• Auxiliary Heat: Supplemental heating that supports the primary system during periods of high demand.
• Azeotrope or Azeotropic Mixture: A blend of two or more compounds that behaves like a single substance with no temperature change during phase transitions, making it inseparable by simple distillation.
• Azeotropic Point: The specific temperature at which an azeotropic mixture boils, producing vapor with the same composition as the liquid.

B

• Balance Point (Heat Pump Balance Point): Outdoor temperature where a heat pump’s output equals home heat loss; below this, backup/aux heat may be needed.
• Backdraft / Spillage: When combustion gases flow back into your home instead of venting outdoors. Often caused by pressure imbalances or blocked chimneys — a serious safety issue that needs a licensed pro.
• BEMS (Building Energy Management System): A computer-based system installed in buildings to control and monitor mechanical and electrical equipment, including ventilation, lighting, power systems, fire systems, and security systems.
• Bioaerosols: Tiny living organisms or fragments of living organisms that are suspended in the air.
• Blend: A mixture of two or more refrigerants combined in specific proportions, which can be separated by distillation and may exhibit temperature glide.
• Blower Door Test: A whole-home test using a special fan to measure air leaks. It helps identify sealing opportunities and ensures your heating and cooling system is right-sized.
• Blower Motor: An electric motor that drives the fan in an HVAC system to circulate air through the system.
• Breaker: An electrical switch designed to protect circuits from damage caused by overloads or short circuits.
• BREEAM (Building Research Establishment Environmental Assessment Methodology): A globally recognized method for assessing, rating, and certifying the sustainability of buildings, first developed in the UK.
• British Thermal Unit (BTU): A unit of heat measurement defined as the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit.
• Bubble Point: The temperature and pressure at which a refrigerant transitions from liquid to gas.
• Boiler: A heating device that heats water for home heating or hot water supply.
• BTUh (British Thermal Units per Hour): A measurement of the heat output per hour of heating equipment.
• Building Envelope: The components of a building’s outer shell that help maintain a controlled indoor environment, aiding in climate control.
• Burner Flame: The flame in a furnace where fuel is burned to produce heat.

C

• C-Wire (Common Wire): A low-voltage wire that provides constant power to modern smart thermostats. Without it, some thermostats can only run on batteries or “steal” power from other wires.
• CAE (Combined Annual Efficiency): A measure of how much heat is produced per dollar of fuel used for both home and water heating systems.
• Capacitor: An electrical component that stores and releases electrical energy, commonly used to start motors in HVAC systems.
• Capacity: The capability of an HVAC system to heat or cool a specific space effectively.
• Capillary Tube: A small-diameter tube serving as a throttling device for refrigerant, ideal for use in environments with constant ambient conditions.
• Carbon Monoxide (CO): A toxic gas resulting from the incomplete combustion of carbon-based fuels.
• Carbon Monoxide Alarm: A device that detects the presence of carbon monoxide in the home and alerts occupants.
• Carbon Usage Effectiveness (CUE): A metric that indicates the ratio of total CO2 emissions from a data center to its IT equipment energy consumption.
• Cascade System: A refrigeration system with multiple refrigerant circuits in series, providing different levels of cooling.
• Cassette Unit: An air conditioning unit designed to fit into suspended ceilings, ideal for cooling large or irregularly shaped rooms.
• Central Air Conditioning: A system that cools and dehumidifies air for an entire building or space using a central cooling unit and a network of ducts to distribute the conditioned air.
• Centrifugal Compressor: A compressor that uses a rotating wheel to compress gas through centrifugal force.
• Centrifugal Fan: A mechanical device that moves air or other gases at an angle to the incoming fluid using centrifugal force.
• CFC (Chlorofluorocarbon): A compound with high ozone depletion potential, banned from use since 2000.
• CFM (Cubic Feet per Minute): A measure of the rate of airflow in an HVAC system.
• Change of State: The transition of a substance from one phase (solid, liquid, gas) to another.
• Chilled Beam System: An energy-efficient convection HVAC system that uses chilled water to cool the air, commonly used in commercial buildings.
• Chilled Water System (CWS): A system that uses water to transfer heat away from the refrigerant in a chiller.
• Chiller: A machine that removes heat from a liquid through a vapor-compression or absorption refrigeration cycle.
• CIBSE (Chartered Institution of Building Services Engineers): A professional association for building services engineers based in the UK.
• CITB (Construction Industry Training Board): A UK organization providing training for the construction industry.
• Clean Room: A controlled environment with low levels of pollutants, used in manufacturing or scientific research.
• Climate Control: A system designed to maintain precise temperature and humidity conditions, often referred to as precision air conditioning.
• Coefficient of Performance (COP): A ratio that measures the efficiency of a heat pump or HVAC system, comparing the heating or cooling provided to the energy consumed.
• Coil: A heat transfer component in an HVAC system, usually a fin and tube heat exchanger.
• Cold Aisle: A data center design where server racks are arranged to create alternating rows of cold air intakes and hot air exhausts.
• Comfort Air Conditioning: HVAC systems designed primarily for human comfort rather than for process operations or equipment cooling.
• Commercial Air Conditioning: HVAC systems used in large buildings like hotels, hospitals, and office complexes.
• Commissioning: The process of verifying and ensuring that HVAC equipment operates according to specifications after installation.
• Compressor: A device in an HVAC system that increases the pressure and temperature of the refrigerant.
• Condensate: The liquid formed when moist air is cooled below its dew point.
• Condensate Drain: A pipe that removes condensation from the air handler and directs it outside or to a drain.
• Condensate Pump: A small pump that moves water from your AC or furnace condensate pan to a safe drain when gravity draining isn’t possible.
• Condenser: A component that condenses refrigerant gas into a liquid by removing heat.
• Condensing Unit: A self-contained unit that includes a compressor and condenser, used in refrigeration and air conditioning systems.
• Conduction: Heat transfer through direct contact between materials of different temperatures.
• Contactor: An electrical relay that controls the flow of electricity to components in an HVAC system.
• Constant Air Volume (CAV): An HVAC system that maintains a constant air flow rate while varying the temperature.
• Controller: A device that regulates the operation of various components within an HVAC system.
• Controls: Systems used to manage and regulate the operation of HVAC equipment.
• Convection: Heat transfer by the movement of a fluid or gas due to changes in density and thermal currents.
• Cooling Tower: A device that cools water by evaporative cooling, commonly used in industrial and large-scale air conditioning systems.
• CRAC (Computer Room Air Conditioning): A unit designed for precise environmental control in data centers.
• CRAH (Computer Room Air Handling): Part of the HVAC system specifically designed for server rooms, focusing on air handling.
• CSA F-280 (Canadian Load Calculation Standard): Canada’s version of Manual J for sizing heating and cooling systems. It uses Canadian climate data, building codes, and insulation standards for accurate load calculations.
• CWR (Chilled Water Return): The portion of the system that returns water back to the chiller after it has absorbed heat.
• Cycling: The process of an HVAC system turning on and off to maintain the desired temperature.

D

• Damper: A movable plate within ductwork that regulates airflow and can be manually or automatically controlled.
• Data Center: A facility designed to house computer systems and related components, such as telecommunications and storage systems, often requiring precise climate control.
• DC (Direct Current): A type of electrical current that flows in one direction, used in various HVAC system components.
• Deadband (Thermostat Differential): A small temperature range around the thermostat setpoint that prevents your system from short cycling.
• Decibel (dB): A unit used to measure the intensity of sound.
• Defrost Cycle: A heat pump mode that briefly reverses operation in winter to melt frost from the outdoor coil. You may notice cool air inside for a few minutes — it’s normal.
• Degree-Day: A unit used to estimate the energy demand for heating or cooling a building based on the difference between the outdoor temperature and a set base temperature.
• Delta T (ΔT): The temperature difference between two points, often referring to the difference between the return air temperature and the supply air temperature in HVAC systems.
• Dehumidification: The process of removing moisture from the air to control humidity levels within a space.
• Dehumidifier: A device that reduces the humidity level in the air, improving comfort and preventing mold growth.
• Density: A measure of mass per unit volume, important for calculating system loads and refrigerant charges.
• Dew Point: The temperature at which air becomes saturated with moisture, causing water vapor to condense into dew.
• Dew Point Control: Managing the dew point in HVAC systems to prevent condensation, which can lead to mold growth and other moisture-related issues.
• Diffuser: An air outlet that evenly distributes airflow from an HVAC system throughout a room.
• Direct Expansion Systems (DX): Air conditioning systems where refrigerant directly expands in the evaporator, absorbing heat from the air.
• DOE (Department of Energy): The U.S. federal department responsible for energy policy and nuclear safety.
• Downflow: An air distribution method where air is pushed downward, typically used in floor-mounted systems.
• Downflow Furnace: A furnace where air enters from the top and heated air exits from the bottom.
• Drain Pan: A component that collects condensation from the HVAC system, preventing water damage and directing moisture away from the system.
• Drop-in: A refrigerant that can replace another without significant system modifications, often used when phasing out older refrigerants for newer, more environmentally friendly options.
• Dry Bulb Temperature: The temperature of air measured by a thermometer freely exposed to the air, without the influence of radiation and moisture.
• Dry-Charged Unit: An air conditioner or heat pump that is charged with refrigerant at the installation site.
• Duct: Passageways used in HVAC systems to deliver and remove air to and from different areas within a building.
• Ductwork: The network of ducts used to transport air from the HVAC unit to various parts of the building.
• Dual Fuel Heat System: A heating system that combines a heat pump with a furnace, using the most efficient fuel source based on outdoor temperature.

E

• EC Fan (Electronically Commutated Fan): Fans equipped with brushless DC motors and built-in electronics to convert AC to DC, offering up to 30% more efficiency and variable speed control.
• Economizer: A device that recycles energy or leverages temperature differences to enhance system efficiency and reduce energy consumption.
• EER (Energy Efficiency Ratio): A measure of system efficiency at specific rating conditions, calculated by dividing the cooling capacity (in kW) by the power input (in kW).
• Efficiency: A measure of how effectively an HVAC system converts energy into heating or cooling.
• Electronic Air Cleaner (EAC): A device that reduces indoor air contaminants by using electronic methods.
• Electronic Expansion Valve (EEV): A valve utilizing a DC stepper motor to precisely control refrigerant flow, ensuring close regulation of evaporator superheat.
• Element: A heater component that converts electrical energy into heat.
• Emergency Heat: A backup heating system activated when the primary heat source is insufficient, often used in extreme cold conditions.
• Energy Star: An EPA program that certifies buildings and products, including HVAC systems, for energy efficiency.
• Energy Technology List (ETL) / ECA Scheme: A UK government program offering enhanced tax relief for investments in energy-saving equipment.
• Energy Efficiency Ratio 2 (EER2): A measure of the efficiency of air conditioners or heat pumps, similar to EER but with updated testing procedures.
• Enthalpy: A thermodynamic property representing the total internal energy plus the heat content of a system, sometimes referred to as total heat.
• Entropy: A measure of the disorder or randomness in a system, related to the rate at which an object absorbs heat.
• Energy Reuse Effectiveness (ERE): A ratio indicating the amount of energy emitted from a data center that is reused elsewhere compared to the total energy consumed.
• Energy Reuse Factor (ERF): The ratio of energy reused within a facility to the total energy input to a data center.
• EPA (Environmental Protection Agency): The U.S. federal agency responsible for environmental protection and regulation of HVAC refrigerants.
• ESEER (European Seasonal Energy Efficiency Ratio): A measure similar to EER but tailored for the European market, accounting for variable load performance across different seasons.
• Evaporator Coil: A component typically located indoors that allows refrigerant to evaporate, absorbing heat from the air passing over it.
• Evaporating Temperature: The temperature at which refrigerant vaporizes inside an evaporator.
• Expansion Valve: A device that regulates refrigerant flow into the evaporator. Types include thermostatic expansion valves, capillary tubes, and fixed orifice devices.
• External Static Pressure (ESP): The total resistance your blower works against in the duct system. High ESP means airflow problems, wasted energy, and noisy operation.

F

• Fahrenheit: A temperature scale where water freezes at 32 degrees and boils at 212 degrees under standard atmospheric pressure.
• Fan: A device consisting of a motor and a blower wheel, designed to create airflow within an HVAC system.
• Fan Motor: The motor that powers a fan, enabling the movement of air within an HVAC system.
• Fan Coil Unit (FCU): A device that includes a heating or cooling coil and a fan, used in residential, commercial, and industrial HVAC systems to control temperature.
• Filter: A component in HVAC systems that removes contaminants from the air or refrigerant. Regular maintenance or replacement is necessary to ensure proper function.
• Filter Bypass: Air that sneaks around the edges of a poorly fitted filter instead of passing through it. Even a high-MERV filter won’t work well if bypass is happening.
• Filter Drier: A device in the liquid line of a refrigeration system that absorbs moisture and traps particulate matter to protect the system.
• Fire Damper: A device installed in ductwork that automatically closes when heat is detected, preventing the spread of fire through the duct system.
• Flooded: A condition where there is excess refrigerant in the evaporator or condenser coils, potentially affecting system performance.
• Flue: A vent that expels the byproducts of combustion from a furnace to the outside.
• Flow Rate: The volume of fluid that passes a specific point in a system over a given period, typically measured in gallons per minute (GPM) or liters per second (L/s).
• Freon: A trade name for a group of CFC and HFC refrigerants commonly used in cooling systems.
• Fresh Air Intake (FAI): An opening through which outdoor air is drawn into the HVAC system, used for combustion or ventilation purposes.
• Furnace: The primary component in a home’s heating system, where fuel combustion occurs to generate heat, which is then distributed throughout the home using a fan.
• Fuse: A safety device in an electrical circuit that protects against excess electrical charge by melting a metal strip to break the circuit.
• Fusible Link: A part of a fire damper that melts at a specific temperature, causing the damper to close and prevent the spread of fire.

G

• Galvanized Steel: Steel coated with zinc to prevent corrosion, commonly used in ductwork construction.
• Garage Heaters: Units providing warmth for garages, often using natural or propane gas.
• Gas: In HVAC terms, this often refers to the refrigerant in its gaseous state.
• Gas Furnace: A furnace that uses natural gas as a fuel source to heat a space by burning the gas in a combustion chamber.
• Gauge Pressure: The pressure reading from a gauge zeroed at atmospheric pressure, allowing for negative readings when below atmospheric pressure.
• Gauges: Instruments used to measure pressure and sometimes temperature within HVAC systems.
• Generator: A device that converts mechanical energy to electrical energy, often used as a backup power source in HVAC systems.
• Geothermal Heat Pump: A system that transfers heat to or from the ground or a body of water, using the earth as a source or sink for heat.
• Glide: The range of boiling temperatures of the different components in a refrigerant blend, affecting the composition of the blend across temperatures.
• Glycol: A fluid with antifreeze properties used in HVAC systems, often circulated through closed-loop systems to transfer heat.
• Glycol-Cooled System: An air conditioning system that uses a water/glycol solution as a condensing medium, with a glycol-cooled condenser typically located inside the air conditioner.
• Grains per Pound (GPP): A unit of measurement for the amount of moisture in the air, indicating the weight of water vapor in a pound of dry air.
• Green Building: A building designed to minimize environmental impact, often incorporating energy-efficient HVAC systems and sustainable materials.
• Grid-Tie Inverter Solar System: A solar power system that allows homeowners to use solar-generated electricity while remaining connected to the utility grid for backup power.
• Grille: An opening or protective barrier, usually louvered, installed at the end of ductwork to direct airflow.
• GWP (Global Warming Potential): A measure of how much heat a greenhouse gas traps in the atmosphere compared to carbon dioxide, with various refrigerants having different GWP values.

H

• Hard Start: A kit used to start a compressor that requires a higher starting voltage.
• HCFC (Hydrochlorofluorocarbon): A type of refrigerant, such as R22, that has a lower ozone-depleting potential and contributes to global warming.
• Heat: In HVAC terms, it refers to the energy transferred between systems that are not in thermal equilibrium.
• Heat Capacity: The amount of heat required to raise the temperature of a given mass by 1 degree Kelvin.
• Heat Exchanger: A device designed for efficient heat transfer between two physically separated fluids.
• Heat Gain: The increase in thermal energy within a space due to sources like solar radiation, equipment, lighting, and occupants.
• Heat Load: The total amount of heat energy that needs to be removed from a space to maintain a comfortable temperature, usually measured in BTUs (British Thermal Units).
• Heat Load Calculation: The process of determining the amount of heat energy that must be added or removed from a space by the HVAC system.
• Heat Loss: The transfer of heat from inside a building to the outside through elements such as walls, windows, roof, and floor, which is crucial for determining heating requirements.
• Heat Pump: A device that absorbs heat from a lower temperature source and transfers it to a higher temperature location to heat a space.
• Heat Pump Cold-Climate Rating: A manufacturer’s capacity data at low outdoor temperatures (such as −15 °C/5 °F). Cold-climate models maintain heat output in BC winters.
• Heat Strip: An electrical heating element in a heat pump that provides supplemental heat during extremely cold temperatures.
• Heat Transfer: The exchange of thermal energy between two interacting media, such as refrigerants, air, and water, typically passing through a heat exchanger.
• Heating Seasonal Performance Factor (HSPF): A ratio measuring the efficiency of a heat pump’s heating capabilities over a typical heating season. It is calculated by dividing the total heating required (in BTUs) by the total electricity consumed (in watt-hours).
• Hemi-anechoic Chamber: A room designed to absorb sound or electromagnetic wave reflections, with a solid floor to support heavy items like air conditioning units for sound level testing.
• HEPA (High-Efficiency Particulate Air): A type of filter capable of trapping a large number of very small particles.
• HFC (Hydrofluorocarbon): A type of refrigerant, such as R134a, that has zero ozone depletion potential but a high global warming potential.
• HFO (Hydrofluoroolefin): A fourth-generation refrigerant, such as R1234ze, with zero ozone depletion potential and low global warming potential.
• High-Performance Computing (HPC): Refers to the aggregation of computing power to solve large problems in science, engineering, or business.
• High Voltage: In HVAC, it refers to electrical voltages higher than 50 volts.
• Horizontal Flow: Describes an air handler or furnace that is positioned on its side.
• Hot Aisle: A design in data centers where server racks are aligned with their hot air exhausts facing the aisle.
• HRAI (Heating, Refrigeration and Air Conditioning Institute of Canada): Canada’s national HVACR trade association offering training, advocacy, and trusted contractor referrals nationwide.
• Humidification: The process of adding moisture to the air within a space.
• HVAC (Heating, Ventilation, and Air Conditioning): The technology focused on indoor and vehicular environmental comfort, aimed at providing thermal comfort and acceptable indoor air quality.
• Hybrid Heat: A dual fuel system that uses both an electric heat pump and a furnace.
• Hydrocarbon Refrigerant (HC): Refrigerants composed of only carbon and hydrogen, such as propane (R290) and isobutane (R600a), with zero ozone depletion potential and very low global warming potential.
• Humidifier: A device that adds moisture to the air.
• Humidistat: A device that measures and controls humidity levels, often used in conjunction with a humidifier.

I

• IAQ (Indoor Air Quality): Refers to the quality of air within and around buildings and structures, particularly regarding the health and comfort of occupants.
• IAQVEC: A Canadian-based nonprofit focused on indoor air quality, ventilation, and energy conservation in buildings through research, publications, and conferences.
• Ignition: The process of raising the temperature of a substance to a point where it undergoes a combustive reaction.
• Industrial Refrigerator: A large-scale refrigeration system used for industrial applications such as food processing, pharmaceuticals, and large commercial facilities, requiring high-capacity cooling.
• Indoor Air Flow: The movement of air inside a building, typically measured in cubic feet per minute (CFM).
• Indoor Coil (Evaporator Coil): A component that absorbs heat from indoor air, usually located inside the air handler or attached to the furnace.
• Insulation: Material used to reduce heat loss or gain by creating a barrier between areas with significantly different temperatures.
• Intermediate Fluid: A fluid used in the secondary loop of a refrigeration system, which is cooled or heated by the primary refrigerant and then used to cool or heat the target space or substance.
• Inverter Compressor: A type of compressor that uses an inverter to control the speed of the compressor motor, allowing for modulation of cooling capacity.
• Interconnection Agreement: A connection or link between power systems that allows them to draw on each other’s reserve capacity during times of need.
• ISO 9000: International standards for quality management and assurance.
• ISP (Internet Service Provider): An organization that provides internet services. While not directly related to HVAC, it is relevant in the context of smart HVAC systems that require internet connectivity.

J

• Joule: A unit of energy in the International System of Units (SI); it is the energy transferred to an object when a force of one Newton acts on that object over a distance of one meter, used in HVAC as a standard unit of energy measurement.
• Jacket Cooling: A cooling method for an engine or compressor where water circulates through a jacket, absorbing heat from the engine or compressor.
• J-T (Joule-Thomson) Effect: The temperature change of a gas or liquid when forced through a valve or porous plug while insulated from the environment, used in refrigeration and air conditioning systems.
• Jumper: A short conductor used to make a connection between terminals or around a break in a circuit.

K

• Kilowatt (kW): A unit of power equal to one thousand watts; in HVAC, it is often used to measure the power consumption of heating and cooling systems.
• Kilowatt-hour (kWh): A unit of energy equivalent to one kilowatt of power expended for one hour; it is the standard unit of energy for billing by electric utilities.
• K-Factor: In HVAC, the K-factor represents the thermal conductivity of a specific material, used to calculate the rate of heat transfer through the material.
• Kickstart: A device used to help start a compressor, particularly under conditions of low voltage or high head pressures.
• Kink: A bend or fold in tubing or piping that restricts fluid flow; in HVAC systems, kinks in refrigerant lines can impede performance and must be avoided during installation.
• Knockout: A pre-cut, removable section of an electrical box or HVAC equipment casing that allows for the passage of cables or ducts.
• Kyoto Protocol: An international agreement aimed at reducing greenhouse gas emissions, influencing HVAC systems by encouraging the use of eco-friendly refrigerants and energy-efficient designs.

L

• Latent Cooling Capacity: The energy required to change the moisture content of the air during the air conditioning process, measured in kg of moisture per kg of dry air.
• Latent Heat: The heat required to convert a solid into a liquid or vapor, or a liquid into a vapor, without changing its temperature.
• Line Set: A pair of copper pipes that connect the outdoor unit (condenser) to the indoor unit (evaporator coil) in a split-system air conditioner or heat pump; it includes a liquid line and a suction line.
• Liquid Line: In HVAC, a pipe that carries refrigerant in its liquid state from the condenser to the evaporator.
• Load Calculation: The process of determining the heating or cooling needs of a space to ensure the HVAC system is appropriately sized, considering factors like area size, insulation, and occupancy.
• Lockout Temperature (Aux/Heat Pump Lockout): A thermostat setting that stops the heat pump below a certain temperature or prevents backup heat above a certain temperature. Used to balance comfort and energy cost.
• Low Pressure Stage: In a refrigerant system, this is the section from the outlet of the expansion device to the compressor suction inlet, where the lowest temperature is achieved in multi-stage systems.
• Low Voltage: Electrical energy that operates at lower voltages than the main power supply, typically used for thermostats and controls in HVAC systems.
• Louver: An arrangement of parallel blades or slats designed to permit airflow while blocking direct light or rain, used in HVAC for ventilation and equipment protection.
• Low Boy: A type of furnace with a lower height, designed to fit in tight spaces.

M

• Make Up Air Unit (MUA): An intake supply fan designed to replace air that has been exhausted from a building; it may be heated or cooled to minimize the impact on the building’s climate control systems.
• Manufacturer Approved System: A system where the components, such as a condensing unit, furnace, or air handler, are approved by the manufacturer and matched according to AHRI standards; installation of unmatched systems is strongly discouraged.
• Matched Systems: HVAC systems where the indoor and outdoor units are designed to work together for optimal efficiency and performance.
• Media: The filtering material in an air filter that captures dirt, dust, mildew, or bacteria.
• Megger: A brand of high-voltage test equipment used to measure insulation resistance.
• MERV Rating (Minimum Efficiency Reporting Value): A standard that rates the overall effectiveness of air filters; higher MERV ratings correspond to finer filtration, meaning fewer dust particles and other airborne contaminants can pass through the filter.
• Metering Device: A component in an HVAC system that regulates the flow of refrigerant to the evaporator.
• Micron: A unit of measure equal to one millionth of a meter, used to describe the size of particles that an air filter can capture.
• Microchannel Coil: A type of coil constructed from parallel flow aluminum tubes mechanically brazed to enhanced aluminum fins, offering improved heat transfer and a more compact, lighter, and corrosion-resistant design.
• Mini-Split: A type of ductless heating and cooling system that allows for individual temperature control in different rooms or spaces within a building.
• Mineral Oil: A lubricant used with certain refrigerants, known for its low moisture absorption properties.
• Minimum Outside Air: The least amount of outdoor air that needs to be introduced into a building to maintain indoor air quality.
• Multipoise: A term used to describe a furnace that can be installed in different positions, such as upright or horizontal, to fit the space where it is being installed.
• Multi-meter: A portable instrument used to measure electrical voltage, current, and resistance.

N

• NATE Certification (North American Technician Excellence): A certification program for HVAC technicians that validates their knowledge and skills in the field.
• Natural Refrigerant: Non-fluorochemical refrigerants such as ammonia (R717), carbon dioxide (R744), and hydrocarbons (e.g., propane R290) that naturally occur in the environment; they have low Global Warming Potential (GWP) and Ozone Depletion Potential (ODP).
• Nanotechnology: The manipulation and application of materials and devices at the nanoscale, which holds potential for innovations in HVAC equipment and materials.
• Near Azeotrope: A chemical mixture formed by combining compounds with nearly identical vapor and liquid compositions, characterized by a temperature glide of less than 2ºC.
• Negative Pressure: A condition where the pressure inside an enclosed space is lower than the pressure outside, often used to control air movement and contamination.
• Needle Valve: A valve with a slender, pointed stem used for precise control of refrigerant flow in HVAC systems.
• NEMA (National Electrical Manufacturers Association): An organization that sets standards for electrical equipment, including motors used in HVAC systems.
• Net Metering: A utility service that allows homeowners to receive credit for self-generated electricity, such as from solar panels.
• Nitrogen Purge: The process of using nitrogen gas to remove moisture and contaminants during HVAC system maintenance or repairs.
• Non-Condensable Gas: Gas in a refrigeration system that does not condense at the condenser’s temperature and partial pressure, often resulting from air leakage and leading to higher head pressure.
• Non-Contact Voltage Tester: A tool used by HVAC technicians to detect the presence of voltage without direct electrical contact.
• Noise Criteria (NC): A standard rating system used to measure and describe indoor noise levels in HVAC systems and spaces.
• Non-Programmable Thermostat: A basic thermostat that does not allow for scheduled temperature changes.
• Normal Operating Range: The typical range of conditions within which an HVAC system operates effectively and efficiently.
• NOx (Nitrogen Oxides): Pollutants produced by combustion processes in HVAC systems, which can have adverse environmental and health effects.
• NSF (National Sanitation Foundation): An organization that develops and sets standards for sanitation, including those related to food service equipment and commercial refrigeration.
• NPLV (Normalized Part Load Value): A measure of chiller efficiency at part-load conditions, representing energy performance during typical operating scenarios.
• Nuisance Tripping: Unexpected and repeated tripping or shutting down of HVAC equipment due to various issues, such as electrical faults or sensor malfunctions.
• NVR (Negative Volumetric Ratio): The volume of refrigerant vapor compared to the volume of the same mass of liquid refrigerant at a given pressure.
• Nut Driver: A hand tool used by HVAC technicians for tightening or loosening nuts and bolts.
• N+1 Redundancy: A system design that ensures availability in case of component failure by having at least one independent backup component for every primary component.

O

• ODP (Ozone Depletion Potential): A measure of a substance’s potential to deplete the ozone layer in the Earth’s stratosphere, commonly associated with older refrigerants like CFCs and HCFCs.
• Off-Gassing: The release of volatile organic compounds (VOCs) or other chemicals from materials, products, or substances over time, potentially affecting indoor air quality.
• Off-Grid or Off-The-Grid System: An independent electricity-generating system that is not connected to the utility grid.
• Oil Furnace: A heating system that converts heating oil into heat for residential use.
• Ohm: The unit of electrical resistance, symbolized by Ω, which determines how easily electric current can flow through a conductor.
• Operating Cost: The expenses associated with running and maintaining HVAC equipment, including energy consumption and maintenance costs.
• Open Loop System: A type of geothermal heat pump system that uses groundwater as a heat source or sink.
• Outdoor Air: Air from the external environment, typically drawn into HVAC systems for ventilation, heating, or cooling purposes.
• Outdoor Coil (Condenser Coil): A component of an air conditioning or heat pump system located in the outdoor unit, releasing heat absorbed from indoor air during the cooling cycle into the outdoor air.
• Outdoor Unit: The outdoor component of a split HVAC system that contains the condenser coil, compressor, and other parts responsible for releasing heat into the external environment.
• Outside Air Damper: A device that controls the flow of outdoor air into a building’s ventilation system, allowing for fresh air intake.
• Outside Air Temperature: The ambient temperature of the outdoor environment, which can impact the operation and efficiency of HVAC systems.
• Overload: A condition where an electrical circuit or component carries a current higher than its designed capacity, which can lead to overheating and damage.
• Overcurrent: An electrical condition where the current flowing through a circuit exceeds the rated current or capacity of the equipment or conductor, typically caused by short circuits or overloads.
• Oversizing: The practice of installing HVAC equipment that is larger or has a higher capacity than required, leading to inefficient operation and higher energy costs.

P

• Packaged Unit: A heating and cooling system with all components housed in one outdoor unit.
• Particles: Tiny substances in the air, including dust, dirt, bacteria, and viruses.
• Particulate Filter: A filter that removes particles from the air, such as dust and pollen.
• Pascals (Pa): The unit of measurement for pressure used in HVAC systems.
• Payback Period: The time it takes for the savings from an HVAC system to equal the initial investment cost.
• PEX Tubing: A type of flexible plastic piping used for water lines in HVAC systems, known for its heat resistance and durability.
• Pilot Light: A small, continuous flame used to ignite the gas burner in older HVAC systems.
• Piping: The conduits that carry refrigerant, water, or gas in and out of HVAC systems.
• Piston (Metering Device): A component in an HVAC system’s compressor that helps regulate the flow of refrigerant.
• Pitch: The inclination angle of ductwork which facilitates proper drainage of condensate in certain parts of the system.
• Plenum: A central distribution box for circulating air in ductwork, used for both supply and return air.
• Plenum Space: The area of a building that provides pathways for HVAC and sometimes wiring, typically above a drop ceiling or under a raised floor.
• Positive Pressure: A condition where the pressure inside an enclosed space is greater than the pressure outside.
• Pressure Balancing: The method of adjusting the HVAC system to ensure balanced air pressure across different areas.
• Pressure Drop: The reduction in pressure as air flows through ductwork or components in an HVAC system.
• Pressure Relief Valve: A safety device that relieves pressure in the system if it becomes too high.
• Pressure Switch: A safety device that monitors the pressure in the HVAC system and shuts it down if necessary.
• Preventive Maintenance: Routine maintenance to keep an HVAC system running efficiently and to prevent breakdowns.
• Programmable Thermostat: An electronic thermostat that adjusts the system’s operations based on programmed settings.
• Propeller Fan: A fan used in HVAC systems for moving air, with blades similar to a propeller.
• PSI (Pound per Square Inch): A unit of pressure measurement used in HVAC to gauge system pressure levels.
• Psychrometrics: The study of the physical and thermodynamic properties of gas-vapor mixtures.
• PTAC (Packaged Terminal Air Conditioner): A self-contained heating and air conditioning system often found in hotels.
• Purge Cycle: The process of removing impure refrigerant or air from a part of the HVAC system.
• Purge Unit: A device that eliminates non-condensable gases from a refrigeration system.
• PURON: A brand name for the refrigerant R-410A, used by Carrier and Bryant.
• PVC (Polyvinyl Chloride): A type of plastic used for condensate drain lines in HVAC systems.

Q

• Quadrant Damper: A type of damper characterized by a quadrant-shaped mechanism that allows for the adjustment of the damper blade position to regulate airflow.
• Quick Connect/Disconnect: Fittings used on HVAC equipment that can be connected or disconnected without the use of tools, often used for gauges and hoses in refrigerant lines.
• Q-Value (also called Q-Factor): In HVAC, it refers to the thermal quality of a material or system, essentially a measure of heat flow resistance; also used in acoustics to describe how underdamped an oscillator or resonator is, relevant to HVAC in terms of noise and vibration control.
• Quenching: The process of rapidly cooling a hot material, such as in the manufacturing of certain HVAC components; also refers to rapid cooling within refrigeration cycles.

R

• R-Value: A measure of thermal resistance for insulation materials; it indicates the material’s ability to resist heat flow, with higher values representing better insulation.
• Radiant Barrier: A type of insulation that reflects radiant heat away from the living space, enhancing energy efficiency.
• Radiant Ceiling Panels: Heating devices mounted on the ceiling that provide warmth through infrared radiation.
• Radiant Floor: A heating system installed beneath the floor, which warms the room by radiating heat upward.
• Radiant Heating: A heating method that uses infrared radiation to heat surfaces directly, rather than heating the air.
• R1234ze (HFO Refrigerant): An eco-friendly refrigerant with very low Global Warming Potential (GWP), used as an alternative to traditional refrigerants.
• HFO-1234ze(E) (HFO Refrigerant): An ultra-low GWP (<1) refrigerant classified A2L (mildly flammable). Often used in chillers and advanced heat pump systems.
• R134a (HFC Refrigerant): A non-ozone-depleting refrigerant commonly used in automotive and commercial cooling applications.
• R22 (HCFC Refrigerant): An ozone-depleting refrigerant being phased out due to environmental regulations.
• R-290 (Hydrocarbon Refrigerant – Propane): A natural refrigerant with ultra-low GWP (≈3). Highly efficient but flammable, mainly used in small systems and appliances.
• R-32 (HFC Refrigerant): A low-GWP (675) refrigerant classified A2L (mildly flammable). Used in ductless systems and heat pumps as a more efficient alternative to R-410A.
• R407C (HFC Refrigerant): A blend of refrigerants used as a replacement for R22, offering improved efficiency and lower environmental impact.
• R410A (HFC Refrigerant): A high-efficiency refrigerant commonly used in newer HVAC systems, serving as a replacement for R22.
• R-454B (HFO/HFC Blend Refrigerant): A next-generation replacement for R-410A with very low GWP (466). Classified A2L for mild flammability, now common in new Canadian heat pumps and ACs.
• R-469A (HFC/HFO/CO₂ Blend Refrigerant): A non-flammable A1 refrigerant blend for ultra-low-temperature applications (down to −70 °C). Contains CO₂, R-32, and R-125.
• R-744 (Natural Refrigerant – Carbon Dioxide): An eco-friendly refrigerant with zero ozone depletion and GWP of 1. Non-flammable but operates at very high pressures; used in commercial and cold-climate systems.
• Rack: In HVAC terms, it can refer to structures holding HVAC components, although it is more commonly a term used in computing.
• Reclaim: The process of processing and upgrading used refrigerant for reuse.
• Recovery: The act of removing refrigerant from a system to be recycled or disposed of properly.
• Reciprocating Compressor: A type of compressor that uses pistons to compress refrigerant, commonly found in residential and commercial HVAC systems.
• Recycle: The process of cleaning recovered refrigerant before it is reused in a system.
• Refrigerant: A fluid used for heat transfer within a refrigeration system, essential for the cooling process.
• Refrigerant Charge: The specific amount of refrigerant required for a system to operate efficiently.
• Refrigeration Cycle (Vapour Compression Cycle): The cycle that refrigerant undergoes in a closed system to facilitate cooling, involving compression, condensation, expansion, and evaporation.
• Refrigerant Lines: Pipes that carry refrigerant to and from the various components of an HVAC system.
• Register: An adjustable air outlet used for distributing conditioned air into a space.
• Relative Humidity (%RH): The ratio of the current moisture in the air to the maximum possible moisture at the same temperature, expressed as a percentage.
• Relay: An electrical device that uses an electromagnet to open or close another circuit in response to a current or signal.
• Remote Electronic Expansion Valve (REEV): An expansion valve that can be controlled remotely to regulate refrigerant flow.
• Remote Room Sensor: A device that measures average conditions in a room to provide data for the HVAC system.
• Reversing Valve: A valve in heat pumps that reverses the flow of refrigerant when switching between heating and cooling modes.
• Return Air: Used air that is returned to the HVAC system for reconditioning and recirculation.
• Return Ducts: Ducts that carry return air back to the HVAC system.
• Return Vent: The component of the ductwork that allows air to return to the furnace or air handler.
• Retrofit: The process of updating or modifying existing HVAC systems to improve performance or efficiency.
• RCI (HI) and RCI (LO): Metrics used to measure the efficiency of server rack cooling in data centers.
• Riello Burner: A high-efficiency burner commonly used in oil furnaces.
• R-Number: The ASHRAE-assigned number used to identify recognized refrigerants.
• Rotary Compressor: A type of compressor that uses rotating elements instead of pistons to compress refrigerant.
• Rotary Screw Compressor: A compressor that uses interlocking screws to compress refrigerant.
• Rooftop Unit (RTU): An air-handling unit typically installed on the roofs of commercial buildings.
• Return Air Plenum: The space where return air is collected before being recirculated into the HVAC system.
• Return Side: The part of the HVAC system responsible for returning air to be reconditioned.

S

• Saturation: The point at which a liquid can no longer dissolve in a solution or a vapor in a gas, relative to temperature and pressure.
• SCC (Standards Council of Canada): Canada’s federal accreditation body for HVAC standards and standard-setting organizations, including those behind CSA F-280.
• Scroll Compressor: A type of compressor used in HVAC systems that operates with two spiral-shaped scrolls to compress the refrigerant.
• SEER (Seasonal Energy Efficiency Ratio): A measure of the cooling efficiency of an air conditioner or heat pump over a typical cooling season.
• SEER 2 (Seasonal Energy Efficiency Ratio 2): Measures the efficiency of central air conditioners and heat pump systems.
• Sensible Heat: The heat that causes a change in temperature of a substance but does not contribute to a change in phase.
• Sensible Heat Ratio (SHR): The ratio of sensible heat to total heat in an HVAC system’s process air stream.
• Sequencer: A device in electric heaters that controls the order in which heating elements turn on and off.
• Setback Thermostat: A thermostat that can change the temperature setting automatically at different times of the day.
• SHGC (Solar Heat Gain Coefficient): A measurement of how well a window blocks heat from sunlight.
• Short Cycling: When your system turns on and off too often. It usually means oversizing, airflow issues, or control problems. Short cycling raises energy bills and wears out equipment faster.
• Short to Ground: A fault condition where an electrical circuit unintentionally connects to the ground or earth.
• Sling Psychrometer: A tool used to measure relative humidity by using the difference in temperatures between a wet bulb thermometer and a dry bulb thermometer.
• Solenoid: An electromechanical device that creates a magnetic field when electric current is passed through it, often used to control valves.
• Smart Recovery and Setback Programming: Manages system efficiency and comfort by adjusting temperatures based on occupancy and schedules.
• Smoke Damper: A damper used in ductwork that automatically closes to prevent the spread of smoke in the event of a fire.
• Soffit Vent: A vent located under the eaves of a roof that allows fresh air to enter an attic space.
• Soft Start: A method for reducing the load and torque in the powertrain and electrical current surge of the motor during startup.
• Sone / dB (Sound Ratings): Noise ratings for fans and outdoor units. Lower numbers mean quieter operation — important for bedrooms and outdoor living areas.
• Sound Attenuator: A device designed to reduce noise in duct systems.
• Space Heater: A self-contained appliance that provides heat to a single room or space.
• Split System: An HVAC system where the condensing unit is placed outside the building and the evaporator coil is inside, often connected to a furnace or air handler.
• Splitter Damper: A damper used in a branch duct to adjust airflow.
• Spill Air: Air that is deliberately exhausted to balance air pressures within a building.
• Sprung: A term sometimes used to describe a duct that has expanded or “sprung” out of its intended shape, often due to pressure or damage.
• Stack Effect: The movement of air into and out of buildings driven by indoor-to-outdoor temperature differences.
• Stale Air: Air that lacks freshness because it has been sitting idle or has been recirculated too long.
• Start Capacitor: A device that provides the extra energy needed to start the compressor or a motor.
• State: The physical form of a substance, such as solid, liquid, or gas.
• Starved: An HVAC condition where the system has an insufficient amount of refrigerant, affecting its cooling or heating capacity.
• Static Pressure: The pressure exerted by a fluid at rest in a ductwork system.
• Steam Humidifier: A device that adds moisture to the air by heating water to produce steam.
• Stratification: The layering of air due to different temperatures, where warmer air rises and cooler air settles at the bottom.
• Sub-base: The mounting base for a thermostat.
• Subcooling: The process of lowering the temperature of liquid refrigerant below its condensation point at a given pressure.
• Suction Line: The pipe that carries refrigerant vapor from the evaporator to the compressor.
• Supply Air: The conditioned air delivered to the living space from the HVAC system.
• Supply Duct: The ductwork that carries conditioned air from HVAC equipment to the living or working space.
• Supply Plenum: The component of the HVAC system that receives air from the supply fan and distributes it to the conditioned space via the supply duct system.
• Supply Side: The portion of the HVAC system that involves the delivery of conditioned air.
• Superheat: The temperature of vaporized refrigerant above its boiling point at a given pressure.
• Swamp Cooler: A type of evaporative cooler that cools air by passing it over water-saturated pads.
• System Balancing: Adjusting the HVAC system to provide the right amount of air to each room or space.

T

• Temperature Differential: The difference in temperature between two points, such as the supply air and the return air in a heating or cooling system.
• Temperature Setback: A method of reducing heating and cooling energy consumption by adjusting the thermostat to a lower temperature during periods of unoccupancy or sleep.
• Thermal Break: A material of low thermal conductivity placed in an assembly to reduce or prevent the flow of thermal energy between conductive materials.
• Thermal Bridging: The movement of heat across an object that is more conductive than the materials around it, undermining the insulating properties.
• Thermal Comfort: A state of mind that expresses satisfaction with the surrounding environment, often achieved when the HVAC system properly regulates indoor temperature, humidity, and airflow.
• Thermal Energy Storage: A technology that stores thermal energy for later use, enhancing energy efficiency and reliability.
• Thermal Envelope: The part of a building that serves as the barrier between the heated or cooled interior spaces and the unconditioned outdoor environment or unheated spaces.
• Thermal Expansion Valve (TXV): A precision device used to meter the flow of refrigerant to the evaporator while controlling the amount of superheat at the outlet of the evaporator.
• Thermal Load: The amount of heating or cooling energy needed to maintain indoor comfort conditions.
• Thermal Zone: An area or space in a building that has its temperature controlled independently from other areas or spaces.
• Thermistor: A type of resistor whose resistance varies significantly with temperature, used as a temperature sensor.
• Thermocouple: A sensor used to measure temperature, consisting of two different conductors that produce a voltage when there is a difference in temperature between them.
• Thermostat: A device that regulates the temperature of a space by activating heating or cooling systems to maintain the desired temperature.
• Thermostat Learning / Geofencing: Smart thermostat features that adjust schedules automatically or use your phone’s location to save energy while you’re away.
• Thermodynamics: The branch of physical science that deals with the relations between heat and other forms of energy such as work.
• Ton of Cooling: A unit of power used to describe the cooling capacity of an HVAC system, equal to the heat required to melt one ton (2000 pounds) of ice in a 24-hour period, which is 12,000 BTU/h.
• Tonnage: A term describing the cooling capacity of an air conditioning system; one ton is the ability to cool 12,000 BTUs in one hour.
• Total Heat (Enthalpy): The sum of both sensible and latent heat contained in a substance or air.
• Transformer: An electrical device that transfers electrical energy between two or more circuits through electromagnetic induction, often used to step down voltage for control systems.
• Transducer: A device that converts one form of energy to another, commonly used in HVAC systems to convert pressure measurements into an electrical signal.
• Turndown Ratio: The ratio of the maximum fuel input rate to the minimum fuel input rate of a modulating or staging heating appliance.
• Two-Stage Furnace: A furnace with two heat output levels, high for cold winter days and low for milder days, providing greater comfort and efficiency.

U

• U-Value: The rate of transfer of heat through a structure divided by the difference in temperature across the structure; it is expressed in watts per square meter per degree Celsius (W/m²°C).
• UL (Underwriters Laboratories): An independent organization that writes testing standards and tests products for safety, including HVAC equipment.
• Ultraviolet (UV) Lights or Lamps: Used in HVAC to disinfect air, improving air quality by preventing the growth of microbes.
• Unconditioned Space: An area or space in a building that is not heated or cooled and where temperature is not intentionally controlled.
• Unitary System: A self-contained HVAC system with all components in a single unit or a paired indoor-outdoor system.
• Universal Refrigerant Certification: A certification required by the EPA under section 608 of the Clean Air Act that allows individuals to work with and handle various types of refrigerants, often required for HVAC professionals in many regions.
• Upflow Furnace: A furnace that intakes air from the bottom and releases heated air from the top, often installed in basements.
• USGBC (U.S. Green Building Council): An organization that promotes sustainable building practices and is known for its LEED (Leadership in Energy and Environmental Design) certification.
• Upflow Unit: A type of air conditioning system that discharges air into the conditioned space via a top-mounted discharge plenum or through an overhead duct system.
• UPS (Uninterruptible Power Supply): An electrical apparatus that provides emergency power when the main power source fails, which can be critical for maintaining HVAC system operations during power outages.

V

• Vacuum Test: A test to check the integrity of a refrigeration system by drawing a vacuum to ensure no leaks before charging it with refrigerant.
• Vapor Barrier or Seal: Material designed to prevent the transmission of water vapor through building envelopes to protect against moisture-related issues.
• Vapor Compression Cycle: A refrigeration cycle that uses a compressor to increase the temperature and pressure of the refrigerant vapor, facilitating its condensation and heat release.
• Vapor Pressure: The pressure exerted by a vapor in thermodynamic equilibrium with its liquid or solid form at a given temperature.
• Vapor: The gaseous state of a substance that is below its critical temperature and can exist in equilibrium with its liquid phase.
• Variable-Speed Technology: Technology used in HVAC systems to adjust the speed of compressors, fans, and pumps for more efficient operation.
• VAV (Variable Air Volume): A system that regulates the volume of air delivered to a space to maintain comfort conditions.
• Vent: An opening designed to convey air, gases, or vapors from one area to another, often out of a building or space.
• Vent Pipe: A pipe that allows the passage of gases from plumbing systems to the exterior to prevent pressure buildup.
• Vent Stack: A vertical vent pipe that expels sewage gases from the drainage system of a building to the outdoors.
• Ventilation: The mechanical or natural process of supplying and removing air from a space for temperature control and air quality.
• Ventilation Rate: The rate at which outside air replaces indoor air within a space, usually measured in cubic feet per minute (CFM).
• Ventilator: A device that introduces fresh air into a space while expelling stale air to maintain air quality.
• Ventilator, Energy Recovery (ERV): An appliance that transfers heat and moisture between incoming and outgoing air streams to improve efficiency.
• Ventilator, Heat Recovery (HRV): A ventilator that recovers heat from exhausted air to preheat incoming fresh air, thereby reducing energy consumption.
• VFD (Variable Frequency Drive): An electronic controller that adjusts the speed of an electric motor, commonly used for fan and pump motors in HVAC systems.
• VRF (Variable Refrigerant Flow): A system that can provide simultaneous heating and cooling to different zones in a building by varying the flow of refrigerant.
• Volume Damper: A damper installed within the ductwork that can be adjusted to control air volume flow through the duct.

W

• Water-Cooled System: An air conditioning system that uses water to remove heat from the refrigerant in the condenser.
• Watt: The unit of power in the International System of Units (SI) equivalent to one joule per second; used in HVAC to measure the power consumption of devices.
• Wet Bulb Temperature: The lowest temperature that can be obtained by evaporating water into the air at a constant pressure; important for assessing cooling systems’ performance.
• Wet Bulb Thermometer: A type of thermometer with a wetted wick over its bulb, used alongside a dry bulb thermometer to measure humidity.
• Wheel Heat Exchanger: Also known as a rotary heat exchanger or energy recovery wheel, it transfers heat and moisture between two separate airstreams.
• Window Unit: A self-contained air conditioning unit installed in a window or through a wall, providing cooling (and sometimes heating) to the room in which it is installed.
• Working Fluid: A pressurized gas or liquid in a refrigeration cycle that absorbs and rejects heat as it circulates through the system.

X

• Xenon Lamp Weathering Test: A test that uses a xenon arc lamp to simulate the effects of sunlight on materials, assessing their durability and longevity under exposure to UV radiation and weather conditions.

Y

• Yaw: A term often used in the context of airflow and ventilation systems, referring to the angle between the direction of airflow and a reference axis.
• Yield Strength: The stress at which a material begins to deform plastically; important in HVAC for understanding the limits of materials used in constructing system components.

Z

• Zero Energy Building (ZEB): A building with a net energy consumption of zero over a typical year; it produces as much energy on-site as it uses, often through a combination of energy efficiency and renewable energy.
• ZEK 014-4-08/11 Test: A standard test for the outgassing behavior of materials used in vehicle interiors, which can also be relevant for HVAC components in transportation systems.
• Zinc Coating (Galvanizing): A process where a protective zinc coating is applied to steel or iron to prevent rusting; in HVAC, ducts and other components may be galvanized for protection.
• Zone: In HVAC, a zone is an area or space in a building that has its own temperature control.
• Zone Valve: A device used to control the flow of water or steam in a hydronic heating or cooling system for different zones in the structure.
• Zoning System: A zoning system for HVAC uses devices such as dampers in the ductwork to selectively control and redirect air to different parts of a building, providing customized temperature zones.