AFUE
Annual Fuel Utilization Efficiency. A percentage that compares a furnace’s usable heat output with the fuel energy it consumes over a season.
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Glossary Category
Capacity & Efficiency
BTU
British Thermal Unit. The amount of heat required to raise one pound of water by one degree Fahrenheit.
BTUH
British Thermal Units per hour. A rate used to describe heating or cooling capacity.
Capacity
The amount of heating or cooling an HVAC system can deliver under specified conditions.
COP
Coefficient of Performance. A ratio comparing useful heating or cooling output with energy input.
EER2
Energy Efficiency Ratio 2. A cooling-efficiency rating measured at a specific outdoor condition using current test procedures.
HSPF2
Heating Seasonal Performance Factor 2. A seasonal heat-pump heating-efficiency rating.
Load Calculation
An engineering calculation used to estimate a building’s heating and cooling requirements.
SEER2
Seasonal Energy Efficiency Ratio 2. A seasonal cooling-efficiency rating for central air conditioners and heat pumps.
Sensible Heat
Heat that changes air temperature without changing moisture content.
Latent Heat
Heat associated with adding or removing moisture from the air.
Ton
A cooling-capacity unit equal to 12,000 BTUH. It does not describe equipment weight.
Glossary Category
Equipment Types
Air Conditioner
Equipment that removes heat and moisture from indoor air and rejects heat outdoors.
Air Handler
An indoor cabinet containing a blower and usually an evaporator coil, electric heat kit or controls.
Condensing Unit
The outdoor portion of a split air-conditioning system, typically containing the compressor and condenser coil.
Dual-Fuel System
A system that combines a heat pump with a fossil-fuel furnace and changes heat sources based on controls and conditions.
Fan Coil
Another term commonly used for an indoor air handler or coil-and-blower assembly.
Furnace
Heating equipment that warms air using gas, oil, propane or electric resistance heat.
Gas Pack
A packaged HVAC unit that combines gas heating and electric cooling in one outdoor cabinet.
Geothermal Heat Pump
A heat pump that exchanges heat with the ground, groundwater or a suitable water source.
Heat Pump
Equipment that transfers heat and can provide both heating and cooling.
Mini-Split
A ductless or limited-duct heat-pump or air-conditioning system with one or more indoor units.
Packaged System
Heating and cooling equipment contained in one outdoor or rooftop cabinet.
PTAC
Packaged Terminal Air Conditioner. A self-contained through-the-wall unit commonly used in hotels and similar buildings.
Rooftop Unit
A packaged commercial HVAC system installed on a roof or elevated curb.
Split System
An HVAC system with separate indoor and outdoor equipment connected by refrigerant piping.
Variable-Capacity System
Equipment that adjusts compressor output over a range rather than operating only fully on or fully off.
Glossary Category
Refrigeration Cycle & Components
Accumulator
A refrigerant vessel used to help prevent liquid refrigerant from entering the compressor.
Compressor
The component that circulates refrigerant and raises its pressure and temperature.
Condenser
A heat exchanger where refrigerant releases heat and changes from vapor toward liquid.
Electronic Expansion Valve
An electronically controlled refrigerant-metering device, commonly abbreviated EEV.
Evaporator
A heat exchanger where refrigerant absorbs heat and changes toward vapor.
Filter Drier
A refrigerant-circuit component that removes moisture, acids and contaminants.
King Valve
A heavy-duty refrigeration service valve commonly found on receivers or commercial equipment.
Line Set
The insulated suction line and smaller liquid line connecting indoor and outdoor refrigeration components.
Metering Device
A component that controls refrigerant flow into the evaporator.
Receiver
A refrigerant-storage vessel commonly used on systems with varying liquid refrigerant volume.
Refrigerant
A fluid that absorbs and releases heat as it changes pressure, temperature and often physical state.
Reversing Valve
A heat-pump valve that changes refrigerant-flow direction between heating and cooling.
Service Port
An access connection used by trained technicians for pressure measurement, evacuation, recovery or charging.
Sight Glass
A window in a refrigeration liquid line used to observe refrigerant condition or moisture indication.
Subcooling
The amount a liquid refrigerant is cooled below its saturation temperature at the measured pressure.
Superheat
The amount a refrigerant vapor is heated above its saturation temperature at the measured pressure.
Thermal Expansion Valve
A refrigerant-metering valve, commonly abbreviated TXV or TEV, that responds to evaporator conditions.
Glossary Category
Airflow, Ducts & Comfort
Air Balance
The process of adjusting and verifying airflow so rooms or zones receive appropriate air volume.
Blower Door Test
A test that measures whole-building air leakage using a calibrated fan and pressure measurement.
CFM
Cubic feet per minute. A common measurement of airflow volume.
Duct Leakage
Air escaping from or entering ductwork through gaps, damaged sections or poor connections.
Duct Static Pressure
Resistance to airflow within the duct system, measured as pressure.
Ductless System
An HVAC system that conditions spaces without conventional central ductwork.
Envelope Leakage
Uncontrolled air movement through cracks and openings in the building enclosure.
Fresh-Air Ventilation
Controlled introduction of outdoor air into a building.
Return Air
Air drawn from rooms back to the HVAC equipment.
Supply Air
Conditioned air delivered from the HVAC equipment to rooms.
Zoning System
Controls, thermostats and dampers used to divide a ducted system into independently controlled areas.
Glossary Category
Electrical & Controls
Capacitor
An electrical component used to assist motor starting or operation by storing and releasing electrical energy.
Contactor
An electrically controlled switch commonly used to energize compressors, fans or heaters.
Defrost Board
A heat-pump control that manages outdoor-coil defrost operation.
ECM Motor
Electronically Commutated Motor. A high-efficiency motor with built-in electronic controls.
High-Pressure Switch
A safety control that opens when refrigerant-system pressure rises above a set limit.
Low-Pressure Switch
A control that opens when refrigerant pressure falls below a set limit.
Relay
An electrically operated switch used to control another circuit.
Sequencer
A control that stages electric heating elements or other electrical loads.
Thermostat
A control that senses temperature and sends heating, cooling, fan or accessory commands.
Transformer
An electrical device that changes voltage, commonly supplying low-voltage HVAC controls.
Variable-Speed Motor
A motor that can operate at multiple speeds or adjust airflow based on control demand.
Glossary Category
Heating & Combustion
Combustion Air
Air required for proper fuel combustion.
Draft Inducer
A furnace motor and wheel assembly that establishes combustion airflow before ignition.
Flame Sensor
A safety component that confirms burner flame.
Heat Exchanger
A furnace component that transfers heat from combustion gases to household air while keeping the two air streams separate.
Hot-Surface Igniter
An electrically heated ignition component used to light gas burners.
Ignition Control Module
A control that manages furnace ignition and safety functions.
Limit Switch
A safety control that responds to excessive temperature or another operating limit.
Manifold Pressure
Gas pressure supplied to furnace or gas-pack burners after the gas valve.
Thermocouple
A heat-sensing safety device that can generate a small electrical signal to prove a standing pilot flame.
Thermopile
A group of thermocouples that generates a larger electrical output from heat.
Glossary Category
A2L, Safety & Service
A2L Refrigerant
A refrigerant safety classification indicating lower toxicity and lower flammability with low burning velocity.
EPA Section 608
Federal technician-certification requirements for servicing, maintaining, repairing or disposing of covered refrigerant equipment.
Leak Detection
Methods used to locate refrigerant leaks, including electronic detectors, bubble solutions, ultraviolet dye or pressure testing where appropriate.
Recovery
Removing refrigerant from equipment and storing it in an approved recovery cylinder.
Refrigerant Detection System
A sensor-and-control system used in selected A2L equipment to detect refrigerant and initiate specified mitigation actions.
Refrigerant Mitigation System
Another term used for controls that respond to a detected refrigerant release.
Vacuum
A low-pressure condition created during evacuation to remove air and moisture from a refrigeration circuit.
Evacuation
The process of using a vacuum pump and measurement instruments to remove air and moisture before charging a sealed system.
Glossary Category
Commercial Refrigeration
Box Temperature
The air temperature measured inside a cooler or freezer enclosure.
Defrost Cycle
A controlled period used to remove frost or ice from an evaporator coil.
Door Gasket
A flexible seal around a cooler, freezer or refrigerator door.
Head Pressure
A common field term for high-side refrigerant pressure.
Low Side
The lower-pressure portion of the refrigeration circuit, generally including the evaporator and suction line.
High Side
The higher-pressure portion of the refrigeration circuit, generally including the compressor discharge, condenser and liquid line.
Pump Down
A control method that stores much of the refrigerant in the receiver or condenser before the compressor stops.
Reach-In Cooler
A commercial refrigerator accessed through front doors.
Suction Pressure
The refrigerant pressure measured on the compressor inlet side.
Walk-In Cooler
An insulated refrigerated enclosure large enough for a person to enter.
Walk-In Freezer
An insulated low-temperature refrigerated enclosure large enough for a person to enter.
Glossary Category
Warranties, Rebates & Business Terms
Commissioning
The startup, measurement and verification process used to confirm installed HVAC operation.
Extended Labor Warranty
Optional coverage that may pay eligible labor costs for covered repairs under written plan terms.
Manufacturer Parts Warranty
Limited coverage for eligible factory parts that fail under written warranty conditions.
Matched System
Indoor and outdoor HVAC components approved to operate together as a rated combination.
QCN
Quality Contractor Network. A contractor network associated with qualifying TVA EnergyRight programs.
Registration
Submitting equipment information to a manufacturer within the required time for applicable warranty benefits.
Rebate
A payment or credit offered after qualifying equipment or work meets program requirements.
Service Call Fee
A charge for dispatching and diagnosing service, separate from approved repair costs unless stated otherwise.
Warranty Claim
A request for coverage under a manufacturer or extended-service agreement.
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