HVACR Glossary of Terms

BTU

British Thermal Unit. This is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. You'll see this measurement when you look at heating and cooling capacities - for example, your dealer may recommend a 75,000 Btu furnace and a 24,000 Btu air conditioner for your home.

GPH

Gallons Per Hour. You might see this rating if you are looking at an oil furnace. In addition to input and output, an oil furnace also has a rating of gallons per hour, the volume of oil a furnace is capable of burning in 60 minutes.

Ton

You'll often see this as a measurement of the capacity of an air conditioning system. Don't panic, it doesn't measure weight! Just like gas and oil furnaces, air conditioners and heat pumps are rated in Btus. One ton of air conditioning is 12,000 Btus per hour. This means that a "one ton" air conditioning system has the capability of removing 12,000 Btus of heat per hour from your home.

Split System

This describes an air conditioning or heat pump system that is split into two sections - an outdoor section and an indoor section. It won't work without the outdoor section plus an indoor section to move the air.

Packaged System

Packaged units provide both heating and cooling from one unit that is placed outside the home - on the ground, on the roof, or sometimes mounted through the walls of the building. Packaged units come in several combinations of fuel sources - gas heat/electric cooling; heat pump; electric heat/electric cooling; oil heat/electric cooling.

Condensing Unit

This is the outdoor section of a split system air conditioning system. You'll know it best as the air conditioner that sits outside your home.

Air Handler

This is the indoor section of a split system. It can be a dedicated air handler, or could be your furnace. Also known as a fan-coil.

Indoor/Evaporator Coil

If your furnace is the air handler section of your split system, then you'll need an indoor coil added to your furnace to complete the system. The coil transfers heat to give you cool air and also aids in dehumidification. If you do not have a furnace and you have a split system air conditioning system - The Indoor Coil or Evaporator is located in the inside unit.

Outdoor/Condenser Coil

If your furnace is the air handler section of your split system, then you'll need an indoor coil added to your furnace to complete the system. The coil transfers heat to give you cool air and also aids in dehumidification.

Heat Pump

A unit that both cools and heats your home. A heat pump system can be either a split system or a packaged system. A heat pump can be used in conjunction with a gas/oil/LP furnace (using the furnace instead of electric resistance heat when temperatures fall below about 35° F with the addition of a fossil fuel kit) These type of heat pumps are known as dual-fuel heat pumps.

Gas-Pack

Short hand for a packaged system that uses gas fuels such as LP or Natural Gas for the heating process.

Dual Fuel System/Unit

A unit that both cools and heats your home. A dual fuel  system can be either a split system or a packaged system. A dual fuel system is designed to use two types of fuels or energy sources to heat your home. The system determines the most economical fuel to use depending on the outside temperature to heat your home. The systems usually utilize a heat pump and gas heat exchanger as the fuel or energy options.

Mini-split System/Unit

Also, known as a ductless HVAC system, a mini-split system that has no ductwork, so they avoid the energy losses associated with the ductwork of central forced air systems. Duct losses can account for more than 30% of energy consumption for space conditioning, especially if the ducts are in an unconditioned space such as an attic. They are relatively small in size and a great option for room additions.

PTAC (Packaged Terminal/Type Air-Conditioner

A unit that is packaged together in one unit, which is usually mounted in a wall in hotels or motels.

Inverter System/Unit

A unit that contains a modulating compressor. This compressor can run at a variation of capacity ratings to save on energy usage.

Geothermal System/Unit

A Geothermal system uses the earth's ground for a heat or cooling source. Thermal conducting lines are installed in the ground to heat or cool a home. Geothermal Systems can save a homeowner anywhere from 30 to 40% on their energy bill. Geothermal Systems can also use ponds or wells for a heating or cooling source.

Refrigerant Detection System (RDS)

Also known as a refrigerant mitigation system (RMS), is designed to monitor for leaks of refrigerants in HVAC equipment, ensuring safety by detecting harmful gas concentrations and triggering alarms or shutdowns if necessary. These systems are essential for compliance with safety regulations and to prevent environmental damage occupant harm from refrigerant leaks.

Refrigerant Detection System Sensors (RDSS)

Refrigerant detection system sensors are devices designed to identify leaks of refrigerant gases in HVAC and refrigeration systems. They help ensure safety and efficiency by providing early warnings of gas leaks, which can be harmful to both people and the environment.

Metering Device

A Component in air conditioning and refrigeration systems that meters the amount of refrigerant flow into the evaporator.

Thermal Expansion Valve (TXV/TEV)

A valve designed to regulate the rate at which liquid refrigerant flows into the evaporator. This controlled flow maximizes the efficiency of the evaporator.

Electronic Expansion Valve (EEV)

A valve designed to regulate the flow of refrigerant entering a direct expansion evaporator. They do this in response to signals sent to them by an electronic controller. A small motor is used to open and close the valve port. The motor is called a step or stepper motor. Step motors do not rotate continuously. They are controlled by an electronic controller and rotate a fraction of a revolution for each signal sent to them by the electronic controller.

Evaporator

The evaporator is a heat exchanger that allows the refrigerant circulating through it to absorb the heat and change the state of refrigerant to a vapor.

Condenser

The condenser is a heat exchanger that allows the refrigerant circulating through it to release the heat it contains and change the state of refrigerant to a liquid.

Reversing Valve

A component in a heat pumps refrigerant circuit, that changes the direction of refrigerant flow. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa.

Lineset

Usually copper piping that allows refrigerant to flow from the outside condenser to the inside air handler that contains the evaporator.

Filter / Drier (Refrigerant)

A refrigerant filter drier is a device used in HVAC systems to remove moisture and contaminants from the refrigerant, ensuring efficient operation and preventing damage to the system. It combines filtration to trap particles and a drying function to absorb moisture, which is crucial for maintaining the longevity of the HVAC system.

Sightglass (Refrigerant)

A refrigerant sight glass is a transparent device installed in the liquid line of refrigeration systems that allows technicians to visually monitor the flow and condition of refrigerants. It helps indicate whether the refrigerant is in liquid form or if there are bubbles present, which can signal issues like undercharging or moisture in the system.

Compressor

The compressor is the heart of of your refrigeration circuit, which is responsible for circulating and compressing refrigerant. Compressors can be hermetic (sealed) or semi-hermetic (non-sealed, where basic repairs can be made).

Service Port (Refrigerant)

A refrigerant service port is a connection point on an air conditioning system that allows technicians to access the refrigerant for checking levels, recharging, or diagnosing issues. It typically includes a valve that can be opened to add or remove refrigerant.

Service Valve

Service valves allow technicians to isolate specific system parts for maintenance. This capability is crucial for tasks like component isolation and pressure readings.

King Valve

King valves operate like service valves, but may require the packing to be turned to a specific location before operating the valve. They are usually made more heavy duty than service valves. King valves allow technicians to isolate specific system parts for maintenance. This capability is crucial for tasks like component isolation and pressure readings.

Crankcase Heater (CCH)

A electric resistance heater that keeps the crankcase of a compressor warm, which prevents liquid migration to the compressor.

Contactor

An electrical switch, which opens or closes the circuit to a compressor and fan usually.

Capacitor

An electrical component that shifts a phase of voltage to help start an electric motor. Larger capacitors can be used as start capacitors.

Defrost Board

A control board that initiates the defrost of the outdoor coil when certain conditions are met.

Electronically Commutated Motor (ECM)

An electric motor, which function using a built-in inverter and a magnet rotor, and as a result are able to achieve greater efficiency in air-flow systems than some kinds of AC motors. (Although AC current is used for ECM, the ECM’s internal rectifier converts the current to DC voltage).

Variable Speed Motor

An electric motor, which compensates for any added pressure drop introduced to the system. For example, if a duct system layout has an increased static pressure due to a dirty filter, the presence of a media filter or simply because of poor design, the motor will automatically ramp up to ensure that the programmed amount of airflow is delivered. This is accomplished without the use of any additional components.

Ignition Control Module (ICM)

A control board which integrates the operation of all the components required to operate a gas fired furnace or gaspack. This module controls components, such as the: gas valve, pilot valve, ignitor, draft motor or flame sensor.

Combination Gas Valve

A valve that controls the flow of gas in a HVAC system. This valve contains: a manual shutoff, control solenoid, pressure regulator, pilot gas solenoid and optionally a thermocouple sensor.

Thermocouple

A device that converts thermal energy into electrical energy. This device is used to sense a flame or temperature. A thermocouple in a furnace is a safety device that detects whether the pilot light is lit. It generates a small voltage when heated by the flame, which keeps the gas valve open; if the flame goes out, the voltage drops, and the gas supply is shut off to prevent leaks.

Thermopile

A device that converts thermal energy into electrical energy. This device is used to sense a flame. A thermopile in a furnace is used as a safety device that generates voltage from the heat of the pilot light, ensuring that the gas supply is shut off if the pilot light goes out. This helps prevent gas leaks and ensures safe operation of the furnace.

Ignitor

A device that utilizes direct spark or hot surface to ignite gases entering the gas heat exchanger.

Accumulator

A refrigerant vessel that meters refrigerant in the refrigerant circuit to prevent excess refrigerant liquid or oil entering the compressor.

Receiver

A refrigerant storage vessel that stores excess refrigerant when not in circulation or needed.

Orifice

A restricted flow regulator that restricts the flow of a medium such as refrigerant or gas. When used to restrict the flow of refrigerant, it then also becomes a metering device for the refrigerant circuit.

Heat Exchanger

A device used to transfer heat from one medium to another. This is usually the device contained in a gas furnace or gaspack that heats up, while air moves across it to be heated up. There are other types of heat exchangers in the HVAC & refrigeration field, also.

Inducer Draft Motor

An electric motor that induces or pulls air through a heat exchanger.

Forced Draft Motor

An electric motor that forces air through a heat exchanger.

High-Limit Safety

A temperature safety switch that switches a circuit off due to high temperatures.

Pressure Transducer

A refrigerant pressure switch that sends proper voltage signals to an Electronic Control Unit, to determine refrigerant pressures.

Electronic Control Unit (ECU)

An electronic unit that processes signals from electronic transducers to control system components to maintain proper functionality of the system.

Thermostat

A control device that switches the HVAC or Refrigeration systems or devices on and off.

Low-Ambient Kit

An optional kit for HVAC & Refrigeration systems that allows a unit to run normally in cooling mode, when the outside temperatures are colder than the unit is designed for.

Low Pressure Safety Switch

A refrigerant pressure switch that prevents the unit from running when the refrigerant suction pressure is low.

High Pressure Safety Switch

A refrigerant pressure switch that prevents the unit from running when the refrigerant head pressure is high.

Fan Cycling Switch

A refrigerant pressure switch that cycles the fan motor(s) on or off, depending on the refrigerant pressures.

Cut In / Cut Out Switch

A refrigerant pressure switch that cycles the unit on and off, based on the refrigerant pressures.

Draft Hood

A device used on older gas furnaces to bring ambient air into the vent gasses to cool the vent gasses and provide a way for downdrafts to exit without affecting the burner flame.

Duct / Ductwork

This is the metal, fibrous, fabric, pvc or flex that circulates supply and return air throughout the structure.

Flame Rod

A small diameter stainless steel rod on a gas furnace used to sense flame rectification by being placed in the flame.

Hot Surface Ignitor (HSI)

A device that when electricity is passed through, warms to a high temperature to ignite gas burners.

Integrated Furnace Control (IFC)

Integrated furnace control Electronic control used to control most operations for newer gas furnaces including flame safety control, circulating fan control, inducer control and safety sensors.

Flame Rod

A small diameter stainless steel rod on a gas furnace used to sense flame rectification by being placed in the flame.

Gas Burner

A gas furnace burner is a device that mixes fuel gas, like natural gas or propane, with air to create a flame for heating. It is an essential component of a gas furnace, responsible for producing the heat needed to warm a home.

Gas Combustion Chamber

A gas combustion chamber in a furnace is the area where natural gas is burned to produce heat. It mixes fuel with air, ignites it, and allows the resulting hot gases to transfer heat to the air that is circulated throughout the home.

Combination Gas Valve

A valve that controls the flow of gas in a furnace. This valve contains: a manual shutoff, control solenoid, pressure regulator, pilot gas solenoid and optionally a thermocouple sensor.

Integrated Furnace Control (IFC)

An IFC, or Integrated Furnace Control, is a component in a furnace that manages the operation of the heating system, including the ignition process, blower operation, and safety features. It ensures that the furnace runs efficiently and safely by monitoring various system parameters.

Hot Surface Ignitor (HSI)

An HSI, or Hot Surface Igniter, is a component in modern gas furnaces that ignites the gas by heating up to a high temperature, allowing the gas to combust and produce heat. It replaces older pilot light systems and is typically made of materials like silicon carbide.

Limit Switch

A limit switch on a furnace is a safety device that monitors the internal temperature and shuts off the furnace if it gets too hot, preventing overheating and potential damage or fire hazards. It ensures safe operation by controlling the burners and allowing the blower to cool the system when necessary.

Pressure Switch

A pressure switch in a furnace is a safety device that ensures the furnace operates correctly by monitoring the pressure in the exhaust system. It prevents the furnace from igniting if there is insufficient pressure, helping to avoid dangerous situations like carbon monoxide buildup.

Centrifugal Switch

A centrifugal switch in a furnace is a safety device that ensures the furnace operates correctly by monitoring the proper fan speed of an inducer motor in the exhaust system. It prevents the furnace from igniting if there is insufficient rotation, helping to avoid dangerous situations like carbon monoxide buildup.

Flame Rollout Switch

A flame rollout switch is a safety device in a furnace that detects if flames escape from the combustion chamber, preventing potential fires. It trips to shut down the furnace if it senses dangerous conditions, ensuring safe operation.

Heat Sequencer

A heat sequencer in a furnace is a device that controls the order in which heating elements are activated, ensuring they turn on in stages to prevent electrical overload. This helps the furnace operate efficiently and safely by managing the flow of electricity to the heating elements.

Electric Heat Kit (Electric Resistance Heat)

An electric heat kit in a furnace is can be a primary or supplementary heating component that provides heat. It typically includes electric heating elements and is designed to integrate with existing HVAC systems for efficient heating.

Electric Heat Element

An electric heat element in a furnace is a component that converts electrical energy into heat, allowing the furnace to warm the air for your home. It typically consists of tightly-wound metal coils that heat up when electricity passes through them.

Gas Orifices

A gas orifice in a furnace is a small opening that controls the flow of gas into the burner, ensuring proper combustion and efficiency. It is an essential component for regulating the gas supply in heating systems.

LP Conversion Kit

An LP conversion kit allows a furnace designed for natural gas to be converted to use liquid propane (LP) instead. This is useful for homes that do not have access to natural gas pipelines, providing an alternative fuel option.

Flame Sensor

A flame sensor in a furnace is a safety device that detects whether the gas burner is producing a flame. If it does not sense a flame, it shuts off the gas supply to prevent dangerous gas leaks.

Standing Pilot Light

A standing pilot light in a furnace is a small, continuously burning flame that serves as an ignition source for the main gas burner. It is commonly found in older gas furnaces, while modern systems typically use electronic ignition methods.

Gas Venturi

A gas venturi in a furnace is a system that uses the principle of negative pressure to mix gas with air for combustion, allowing for efficient heating. This type of burner typically does not require a combustion air blower, making it simpler and often used in smaller furnaces.

Venturi

A Venturi in a furnace is used to enhance airflow and improve combustion efficiency by creating a pressure difference that draws in air to mix with the fuel. This principle helps in achieving better heat distribution and can potentially reduce the need for additional blowers.

Gas Heat Exchanger

A gas heat exchanger in a furnace is a component that transfers heat from combustion gases to the air that circulates through your home, ensuring that the heated air is free from harmful combustion gases. It typically consists of a series of metal tubes that allow the heat to be exchanged while keeping the toxic gases separate from the indoor air.

Secondary Gas Heat Exchanger

A secondary heat exchanger in a furnace is a component that captures additional heat from the combustion gases after they pass through the primary heat exchanger. This process increases the furnace's efficiency by extracting more heat and allowing water vapor to condense, releasing latent heat.

Collector Box

The furnace collector box is a critical component of a gas furnace that collects and directs combustion gases into the heat exchanger and exhaust system. A furnace collector box leak can cause poor furnace performance, carbon monoxide risk, and safety shutdowns.

Spark Ignitor

A spark ignitor in a furnace is a component that creates a spark to ignite the gas, allowing the furnace to produce heat. It is essential for starting the combustion process and ensuring the furnace operates efficiently.

Liquid Petroluem (LP) Gas Tank

An LP tank, or liquefied petroleum tank, is a storage container for propane gas, which is commonly used as fuel for heating systems, including furnaces. These tanks can be above-ground or underground and are essential for supplying propane to power heating appliances in homes.

Gas Line

A gas line for a furnace is a pipe that delivers natural or propane gas from the main supply to the furnace, allowing it to operate efficiently. It is essential for providing the necessary fuel for heating your home.

Oil Supply System

The oil supply system brings fuel from the storage tank to the burner. It includes an oil tank (external or inside a basement or shop), an oil line, a primary filter, and a pump. The pump may be a gear or Gerotor design, and it pushes oil through the line to the nozzle at a controlled pressure. A heat-resistant strainer and a filter protect the burner from particulates that can clog the nozzle and degrade performance. Maintenance tips for the supply system include checking the filter for debris, inspecting the line for leaks, and ensuring the tank is kept clean and free of water contamination. Some systems use a low-water cut-off or a fuel level sensor to prevent air from entering the line during long periods of inactivity. Proper priming and occasional line bleeding may be necessary after service.

Oil Tank

An oil tank for a furnace is a storage container that holds heating oil, which is used as fuel for oil-burning furnaces. It supplies the oil to the furnace, where it is burned to generate heat for your home.

Oil Level Sensor

An oil level sensor for an oil furnace is a device that measures the amount of oil in the furnace's storage tank. It helps ensure that there is enough fuel for operation and can alert users when oil levels are low.

Oil Line

An oil line for a furnace is a pipe that transports heating oil from the storage tank to the furnace or boiler. These lines are typically made of materials like copper or steel and can be vulnerable to corrosion and leaks over time.

Oil Filter

An oil filter for a furnace is a component that cleans the heating oil by removing impurities and water before it reaches the burner, ensuring efficient operation and preventing damage to the furnace. Regular maintenance and replacement of the oil filter are important for optimal performance and longevity of the heating system.

Oil Pump

An oil pump for a furnace is a device that moves fuel oil from a storage tank to the burner, where it is pressurized and ignited to produce heat. It is essential for the operation of oil furnaces, ensuring a consistent flow of fuel for efficient heating.

Oil Nozzle

An oil nozzle for a furnace is a small component that atomizes fuel oil, allowing it to mix with air and ignite in the combustion chamber to produce heat. It is crucial for the efficient operation of oil-burning heating systems, with different types available based on spray patterns and flow rates.

Oil Combustion Chamber

An oil combustion chamber in a furnace is the area where fuel oil is burned to produce heat. It is designed to contain the flames and transfer the generated heat to the heat exchanger, which then distributes warm air throughout the home.

Oil Burner

An oil burner is a heating device which burns #1, #2 and #6 heating oils, diesel fuel or other similar fuels. In the United States, ultra low sulfur #2 diesel is the common fuel used. It is dyed red to show that it is road-tax exempt. In most markets of the United States, heating oil is the same specification of fuel as on-road un-dyed diesel. An oil burner is a part attached to an oil furnace, water heater, or boiler.

A2L

A2L refrigerants are a relatively recent development in the world of cooling and HVAC systems, representing a new classification of low-global-warming-potential (GWP) refrigerants designed to meet modern environmental standards. The “A2L” designation refers to their safety classification based on flammability and toxicity. Specifically, “A” indicates that they are lower in toxicity, similar to other non-flammable refrigerants, while “2L” signifies that they are mildly flammable, with a lower flammability risk compared to more hazardous refrigerants.

Load Calculation

A load calculation is a method used to determine the heating and cooling needs of a building, ensuring that the HVAC system is properly sized for efficiency and comfort. It takes into account factors like the size of the home, insulation, number of windows, and regional climate conditions.

Balance Point

The balance point refers to the outdoor temperature at which a heat pump's heating output matches the heating demand of a building. Below this temperature, the heat pump cannot meet the heating needs alone and may require supplementary heating sources.

Return Air Temperature (RAT)

Return air temperature refers to the temperature of the air that is pulled back into the system from the living spaces of a building. This air is then filtered and either heated or cooled before being redistributed through the supply vents.

Supply Air Temperature (SAT)

Supply air temperature refers to the temperature of the air that is delivered into a space from the heating, ventilation, and air conditioning system.

Ambient Temperature

This is the air temperature (usually the outdoor air temperature) surrounding the equipment.

Dry-Bulb Temperature

The temperature of air measured by a thermometer freely exposed to the air but shielded from radiation and moisture.

Wet-Bulb Temperature

The temperature a parcel of air would have if it were cooled to saturation (100% relative humidity) by the evaporation of water into it, with the latent heat being supplied by the parcel.

Air Changes per Hour (ACH)

ACH, or Air Changes Per Hour, is a measure of how many times the total volume of air in a room is completely replaced in one hour. It is an important metric in HVAC systems for ensuring adequate ventilation and maintaining good indoor air quality.

Air Changes per Hour @ 50 Pascals (ACH50)

ACH50, or Air Changes per Hour at 50 Pascals, is a standardized measurement used in the HVAC industry to assess the air tightness of a building’s envelope. Essentially, it quantifies how many times the total volume of air within a space can be replaced with outside air in one hour, under a specific pressure differential of 50 Pascals. This test is crucial because it provides a clear, objective measure of a structure’s air leakage, which directly impacts energy efficiency, indoor air quality, and overall comfort.

Humidity

The amount of water vapor in the air. Water vapor is the gaseous state of water and is invisible.

Condensation

Condensation refers to the process where warm, moisture-laden air comes into contact with cooler surfaces, such as evaporator coils, causing water vapor to change into liquid water. This process is essential for cooling and dehumidifying the air.

Condensate

Condensate refers to the water that forms when warm, humid air comes into contact with cold surfaces, such as the evaporator coils in air conditioning systems. This moisture must be drained away to prevent damage and maintain system efficiency.

Emergency Drain Pan

An emergency drain pan is a secondary pan installed beneath the primary drain pan to catch any overflow or leaks from the main system, preventing water damage to the surrounding area. It acts as a safety measure to ensure that if the primary pan fails or overflows, the emergency pan will contain or drain the excess water.

Primary Drain Line

A primary drain line is a pipe that removes excess moisture produced by the air conditioning system, specifically from the condensate drain pan. It is essential for preventing water buildup, which can lead to system malfunctions and water damage.

Auxiliary Drain Line

Also known as a secondary or emergency drain line, an auxiliary drain line is a secondary drainage system designed to handle excess water from the condensate drain pan, typically used to prevent overflow and potential water damage if the primary drain becomes clogged. It is often installed under air conditioning units to direct any overflow to a safe location.

Float Switch

A float switch in HVAC is a safety device located in the air conditioner's drain pan that monitors water levels. If the water rises too high, the float switch automatically shuts off the AC system to prevent overflow and potential water damage.

Ambient

Ambient conditions in HVACR refer to the existing environmental factors present in a given space, which include temperature, humidity, air quality, and overall indoor comfort levels. These conditions serve as the baseline that HVAC systems aim to regulate and maintain within comfortable and safe ranges for occupants. Understanding ambient factors is crucial because they influence the design, efficiency, and effectiveness of heating, ventilation, and air conditioning systems. The most common term of ambient in HVACR is ambient temperature.

Delta T

This describes a temperature difference between two reference points.

Superheat

Any temperature of a gas above the boiling point for that liquid.

Subcooling

The condition where the liquid refrigerant is colder than the minimum temperature (saturation temperature) required to keep it from boiling and, hence, change from the liquid to a gas phase.

Approach Temperature

The the difference between the saturated refrigerant temperature and the leaving air or water temperature.

Static Pressure

The air pressure that is created by the fan blowing air into the ductwork system. The level of static pressure is dependent ability of the fan to increase the pressure and amount of air the outlets are able to remove from the system.

External Static Pressure (ESP)

The measurement of all the resistance in the duct system that the fan has to work against. Examples are filters, grills, A/C coils and the ductwork. It is the sum of the suction pressure (negative) and discharge pressure (positive) created by the equipment blower.

Total External Static Pressure (ESP)

Generally, when measuring total external static pressure, measure the pressure at the point where airflow enters the equipment and where the airflow exits the equipment. The pressure entering the equipment is a suction or negative pressure. The pressure exiting the equipment is a discharge or positive pressure.

Airflow

Airflow in HVAC (Heating, Ventilation, and Air Conditioning) refers to the movement of air through a building's ventilation system, which is essential for maintaining indoor air quality and thermal comfort. It involves the controlled supply of fresh outdoor air and the expulsion of exhaust air, often influenced by factors like duct design and pressure differentials.

Cubic Feet per Minute (CFM) of Airflow

CFM, or Cubic Feet per Minute, is a measurement that indicates the volume of air an HVAC system can move in one minute. It is essential for ensuring proper airflow, maintaining indoor comfort, and optimizing energy efficiency in heating and cooling systems.

Flooded Evaporator

When the evaporator is receiving more refrigerant than needed, which usually results in liquid refrigerant flooding the evaporator.

Starved Evaporator

When the evaporator is not receiving enough refrigerant to perform properly.

Short-Cycle

The term used when an HVAC or Refrigeration unit starts and shuts off quickly.

Suction Pressure

The refrigerant pressure in the vapor line exiting the evaporator and entering the accumulator or compressor.

Head Pressure

Also known as liquid pressure, head pressure is the refrigerant pressure in the liquid line exiting the condenser and entering the metering device or evaporator.

Combustion Air

Air used to supply the burners with enough oxygen to allow complete combustion.

Continuity

An electrical term indicating that the wire or component tested is broken or more accurately has an open circuit.

Shorted

An electrical term indicating that the circuit has bypassed the load and passed through to the other side of the circuit with little or no resistance causing excessive current and consequent opening of circuit protection (fuse or breaker).

Low Voltage

Low voltage typically refers to systems that operate at 12 to 24 volts, which are used to control heating and cooling equipment through signals rather than directly powering them. Most residential HVAC systems utilize low voltage thermostats to manage the operation of the main heating or cooling source.

High Voltage

High voltage typically refers to electrical systems that operate at voltages 120 volts and higher. These systems directly connect to the main electricity circuit and control heating elements, unlike low voltage systems that send signals to control the HVAC system.

Control Circuit

A control circuit is a system that manages the operation of heating, ventilation, and air conditioning equipment by using electrical signals to control various components like thermostats, relays, and motors. It ensures that the HVAC system operates efficiently and maintains the desired indoor climate by responding to inputs such as temperature and humidity levels.

Intermittent Pilot

A pilot burner that only operates when there is a call for heat.

Latent Heat

The heat released or absorbed by a change of state, usually liquid to gas or gas to liquid.

Media

A type of filter that uses a type of paper or fiberglass to catch particles moving thru the ductwork.

Natural Draft

A gas furnace that uses the heat of the burning gasses to move the products of combustion.

Normally Open (NO)

The position of contacts of a switch when power is not applied. Open means no power can pass through.

Normally Closed (NC)

The position of contacts of a switch when power is not applied. Closed means power can pass through.

Original Equipment Manufacturer (OEM)

A part designed for a specific appliance model as opposed to general replacement part.

Open

The position of an electric switch that will not allow electricity to pass through.

Closed

The position of an electric switch that will allow electricity to pass through.

Gas Prepurge

Operation of inducer prior to flame initiation to clear any gasses from the heat exchanger.

Return Air

Ductwork designed to bring air that is circulated through the structure back to the HVAC system.

Full Load Amps (FLA)

Full Load Amperage refers to the maximum current a motor will draw when operating at full capacity. This value is typically found on the motor's nameplate and is crucial for determining overload protection and sizing electrical components.

Run Load Amps (RLA)

Running load amps is the maximum amperage that the air circulating fan motor can draw. The RLA is listed on the model plate of the motor. A much lower reading may indicate blockages in the ductwork. A high reading may indicate failing bearings or a motor that is too small for the application.

Locked Rotor Amps (LRA)

Refers to the maximum amperage the motor will draw when the rotor is locked into position and will not turn.

Roll Out Switch

A high temperature limit switch that must be manually reset placed near the burners to detect flames that have "rolled out" from the front of the furnace.

Stack Temperature

Temperature of exhaust gasses as they leave the heat exchanger.

Lineset

A line set in HVAC is a pair of copper pipes that connect the indoor and outdoor units of a split system air conditioner or heat pump, allowing refrigerant to flow between them. It typically includes a liquid line that carries refrigerant to the indoor unit and a suction line that returns it to the outdoor unit, playing a crucial role in the system's heating and cooling efficiency.

Supply Air

Ductwork designed to bring air that is conditioned through the supply ductwork to the space to be conditioned.

Return Air

Ductwork designed to bring air that is circulated through the conditioned space back to the HVAC system.

Sensible Heat

Heat that can be measured by a thermometer.

Standing Pilot

A gas ignition system that uses a standing pilot to ignite the main gas burners.

Conditioned Space

This is the space of a structure that needs to be heated or cooled.

Unconditioned Space

This is the space of a structure that does not need to be heated or cooled - such as an attic space or crawl space.

Filter Grille

A filter grille in HVAC is a component that combines a grille and an air filter, allowing air to pass through while filtering out dust and other particles. It is typically installed at the intake of return ducts to improve air quality and make filter changes more accessible.

Return Air Filter

A return air filter in HVAC is a component that captures dust, allergens, and other particles from the air being pulled back into the system through return vents. It helps improve indoor air quality and protects the HVAC system from debris buildup.

Supply Duct

A supply duct in HVAC is a component that delivers heated or cooled air from the HVAC unit into various rooms of a building. It pushes conditioned air outward through vents, helping to maintain the desired indoor temperature.

Return Duct

A return duct in HVAC is a component that pulls air from the living spaces back into the heating or cooling system to be reconditioned. It helps maintain proper airflow and indoor air quality by cycling air through filters before it is heated or cooled again.

Branch Duct

A branch duct in HVAC is a smaller duct that extends from the main trunk duct to deliver conditioned air to individual rooms or areas within a building. It helps distribute air efficiently throughout the space, ensuring comfort and proper airflow.

Pittsburg Seam

A Pittsburgh seam is a type of joint used in HVAC ductwork, created by folding and locking the edges of sheet metal together to form a strong connection. It is commonly used for larger ducts and is known for its durability and ability to handle higher pressure compared to other seams.

Duct Plenum

A duct plenum is a sealed air compartment that connects the air handler to the ductwork, distributing conditioned air throughout a building. It plays a crucial role in ensuring efficient airflow and maintaining indoor air quality.

Duct Transition

A duct transition in HVAC is a specialized section of ductwork that connects air conveyance elements of different sizes or shapes, ensuring smooth airflow and minimizing turbulence. Properly designed transitions enhance airflow efficiency, reduce noise, and prevent pressure loss in the system.

Duct End Cap

A duct end cap is a fitting used to seal the open ends of ductwork in HVAC systems, preventing air from escaping and ensuring efficient airflow. They are typically made from materials like metal, plastic, or fiberglass and come in various sizes to fit different duct configurations.

Duct Access Door

A duct access door is a sealed panel or hinged door installed in the ductwork of heating, ventilation, and air conditioning systems, allowing easy access for maintenance, cleaning, and inspections without dismantling the duct system. These doors help ensure efficient operation and compliance with building regulations.

Duct Takeoff

A duct takeoff is a duct component that attaches to the supply duct or branch to direct airflow to the desired area. Takeoffs can contain dampers that allow the airflow to be controlled.

Duct Airtight (AT)

A airtight takeoff is for flat duct that attaches to the supply duct or branch to direct airflow to the desired area. The airtight takeoffcontains a sticky insulation gasket to provide a airtight seal.

Air Handling Unit (AHU)

Also known as an air handler, an air handling unit is a crucial component of an HVAC (heating, ventilation, and air conditioning) system. Its primary function is to regulate and circulate air as part of the larger climate control setup within residential, commercial, or industrial buildings.

Duct Round Airtight with Damper (RATD)

A round airtight takeoff with damper is for round duct that attaches to the supply duct or branch to direct airflow to the desired area. The round airtight takeoff with damper contains a damper that allows the airflow to be controlled. The round airtight takeoff with damper contains a sticky insulation gasket to provide a airtight seal.

AFUE

This is a percentage measurement of a furnace's heating efficiency. The U.S. Government's minimum efficiency level is 78%. The higher the AFUE, the more efficient the furnace. The initials stand for Annual Fuel Utilization Efficiency.

ENERGY STAR

Products/Homes/Buildings that earn the ENERGY STAR prevent greenhouse gas emissions by meeting strict energy efficiency guidelines set by the U.S. Environmental Protection Agency and the U.S. Department of Energy. To learn more, please visit www.energystar.gov.

EER

The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures. SEER rating more accurately reflects overall system efficiency on a seasonal basis and EER reflects the system’s energy efficiency at peak day operations.

EER2

SEER2 is a newer efficiency rating that incorporates stricter testing requirements. EER2, or Energy Efficiency Ratio 2, is a metric used to measure the energy efficiency of air conditioning systems at peak cooling conditions, specifically at an outdoor temperature of 95°F. It provides a more accurate assessment of efficiency compared to the older EER rating by using updated testing procedures that reflect real-world usage conditions. It reflects a unit's performance under real-world conditions, accounting for factors like airflow resistance and cycling losses, and was implemented as a new standard by the Department of Energy in 2023.

SEER

This is a measurement of the efficiency of cooling products. The U.S. Government's minimum efficiency level is 13 SEER for split systems and packaged units. The higher the SEER, the more efficient the cooling product. SEER stands for Seasonal Energy Efficiency Rating.

SEER2

SEER2 is a newer efficiency rating that incorporates stricter testing requirements. SEER2 stands for Seasonal Energy Efficiency Ratio 2, which is a measure of the cooling efficiency of air conditioners and heat pumps. It reflects a unit's performance under real-world conditions, accounting for factors like airflow resistance and cycling losses, and was implemented as a new standard by the Department of Energy in 2023.

HSPF

This is a measurement of a heat pump's heating efficiency. There is no governmental minimum rating. The higher the HSPF, the more efficient the heat pump's heating performance. HSPF stands for Heating Seasonal Performance Factor.

HSPF2

HSPF2 is a newer efficiency rating that incorporates stricter testing requirements. HSPF2 stands for Heating Seasonal Performance Factor 2, a metric that measures the efficiency of a heat pump's heating mode. The higher the HSPF2 rating, the more efficient the heat pump is in converting electricity into heat, leading to potential energy savings and lower energy bills. It reflects a unit's performance under real-world conditions, accounting for factors like airflow resistance and cycling losses, and was implemented as a new standard by the Department of Energy in 2023.

COP

Coefficient Of Performance. A ratio that compares a heat pump system's heating efficiency to that of electric resistance heat. For example, a heat pump system with a COP of 3.0 provides heat at 3 times the efficiency of electric resistance heat. A heat pump's system COP will decrease as outdoor temperatures drop, eventually providing little or no efficiency advantage over electric resistance heat - and that's when your auxiliary heat strips start to heat your home.

R-12

Dichlorodifluoromethane (R-12), usually sold under the Freon-12, is a halomethane (CFC), used as a refrigerant and aerosol spray propellant. Complying with the Montreal Protocol, its manufacture was banned in the United States along with many other countries in 1994 due to concerns about damage to the ozone layer. It is soluble in many organic solvents.

R-134A

Also called simply tetrafluoroethane, R-134a, Genetron 134a, Suva 134a or HFC-134a, is a haloalkane refrigerant with thermodynamic properties similar to R-12 (dichlorodifluoromethane), but without its ozone depletion potential.

R-22

(HCFC) It is better known under its code names of HCFC-22, R-22, Genetron 22 or Freon 22, and is commonly used in air conditioning applications, such as residential split systems in the US, rooftop units and window air conditioners. It will soon be phased out due to ozone depletion potential and status as a potent greenhouse gas. All air-conditioning and heating equipment that uses R-22 will cease production of such by January 1, 2010. The refrigerant supply and production of R-22 will then be slowly cut back and banned by January 1, 2020.

R-32

R-32, also known as difluoromethane, is a hydrofluorocarbon refrigerant with a low global warming potential (GWP) of 675 and zero ozone depletion potential (ODP). It is increasingly used in HVAC systems as a more environmentally friendly alternative to older refrigerants like R-410A.

R-404A

A blend of HFC refrigerants commonly used for medium and low temperature refrigeration applications. It’s composition comprises: HFC-125 (44%), HFC-143a (52%), HFC-134a (4%). It is non toxic and non flammable meeting the highest A1/A1 classification.

R-407C

A mixture of hydrofluorocarbons used as a refrigerant. It is a zeotropic blend of difluoromethane, pentafluoroethane, and 1,1,1,2-tetrafluoroethane

R-407F

A blend of HFC refrigerants designed to replace R22, R404A and R507 in low temperature refrigeration applications. Major compressor manufacturers including Bitzer and Copeland have endorsed its use in their equipment. It's composition comprises of HFC-32, HFC-125 and HFC-134a. It is non toxic and non flammable meeting the highest A1/A1 classification.

R-408A

A blend of HCFC refrigerants introduced to retrofit R502 in medium and low temperature refrigeration applications.It’s compositon is made up of HFC-125 (7%), HFC-143a (46%), HCFC-22 (47%)

R-409A

A blend of HCFC refrigerants introduced to retrofit R12 in air conditioning and refrigeration applications. It’s compositon is made up of HCFC-22 (60%), HCFC-124 (25%), HCFC-142b (15%).

R-410A

Sold under the trademarked names Puron, Genetron R410A, and AZ-20, is a near-azeotropic mixture of difluoromethane (CH2F2, called R-32) and pentafluoroethane (C2HF5, called R-125) 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 phased out. However, it has a high global warming potential of 1725 (1725 times the effect of carbon dioxide), similar to that of R-22.

R-427A

A blend of HFC refrigerants designed to retrofit R22 installations. R22 is a HCFC and therefore being phased out in Australia. R427A offers similar performance to R22 usually without any need for modification to the existing R22 installation. It can be used to retrofit low temperature refrigeration equipment and air conditioning installations. It is non toxic and non flammable meeting the highest A1/A1 classification. R427A, as a blend of HFCs, requires polyolester (POE) lubricants but is tolerant of high levels of alkylbenzene or mineral oils of up to 10%.

R-438A

(MO99) A versatile R22 replacement refrigerant. It combines R22 pressure-enthalpy characteristics with mineral oil compatibility in a unique HFC refrigerant that can be used in R22 replacement over a wide range of evaporator temperatures. As an R22 replacement, R438A may be used in a wide range of applications and has advantages over other R22 replacements. R438A has been designed to closely match the pressure, temperature, enthalpy, and mass flow properties of R22, for a seamless R-22 replacement. R438A has a 42% lower global warming potential (GWP) than R404A. R438A matches R22 in terms of capacity and efficiency in most systems, but with a significantly lower discharge temperature which may prolong life of the compressor. It’s compatible with traditional and new lubricants, providing quick, cost-effective R22 replacements and can be topped off during service without removing the entire refrigerant charges. For most R22 systems, when retrofitting to R438A all you need to do is recover the R22, replace critical seals, charge refrigerant, restart and monitor for leaks, label the system, and you’re done. R22 replacement can’t get any easier.

R-454B

R-454B, also known by the trademarked names Opteon XL41, Solstice 454B, and Puron Advance, is a zeotropic blend of 68.9 percent difluoromethane, a hydrofluorocarbon, and 31.1 percent 2,3,3,3-tetrafluoropropene, a hydrofluoroolefin. Because of its reduced global warming potential, R-454B is intended to be an alternative to refrigerant R-410A in new equipment. R-454B has a GWP of 466, which is 78 percent lower than R-410A's GWP of 2088.

R-507

Sometimes referred as AZ50, is a blend of HFC refrigerants commonly used for medium and low temperature refrigeration applications. It’s composition comprises: HFC-125 (50%), HFC-143a (50%). It is non toxic and non flammable meeting the highest A1/A1 classification.