HVAC Dictionary
Complete glossary of heating, cooling, and ventilation terms explained in simple language
A
AFUE
Annual Fuel Utilization Efficiency - A measurement of furnace heating efficiency. Higher AFUE ratings indicate more efficient furnaces.
Air Handler
The indoor unit of a split HVAC system that contains the blower, evaporator coil, and sometimes heating elements.
AHRI
Air-Conditioning, Heating, and Refrigeration Institute - Organization that certifies HVAC equipment performance.
ACH
Air Changes per Hour - The number of times the total air volume in a space is replaced in one hour.
Accumulator
A device that prevents liquid refrigerant from entering the compressor in heat pump systems.
B
BTU
British Thermal Unit - The amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit.
Blower
The fan component that circulates air through the ductwork and living spaces.
Boiler
A heating system that heats water or produces steam for distribution through radiators or radiant floor systems.
C
CFM
Cubic Feet per Minute - A measurement of airflow volume.
Compressor
The component that pressurizes refrigerant and circulates it through the system.
Condenser
The outdoor unit component where refrigerant releases heat and condenses from vapor to liquid.
COP
Coefficient of Performance - The ratio of heating or cooling output to energy input.
Capacitor
An electrical component that stores energy and helps motors start and run efficiently.
D
Damper
A movable plate in ductwork that regulates airflow to different zones or rooms.
Delta T
The temperature difference between supply and return air, indicating system performance.
Ductwork
The system of metal or flexible tubes that distributes conditioned air throughout a building.
Defrost Cycle
The process where a heat pump reverses operation to melt ice from outdoor coils.
E
EER
Energy Efficiency Ratio - Cooling efficiency rating at a specific outdoor temperature (95°F).
Evaporator Coil
The indoor coil where refrigerant absorbs heat and evaporates from liquid to vapor.
ENERGY STAR
EPA program certifying energy-efficient products that meet strict efficiency guidelines.
ECM
Electronically Commutated Motor - A variable-speed motor that adjusts airflow for optimal efficiency.
F
Furnace
A heating system that burns fuel or uses electricity to heat air for distribution.
Filter
A device that removes particles from air passing through the HVAC system.
Freon
A brand name for refrigerants, commonly R-22 (being phased out) or R-410A.
Flue
The vent pipe that exhausts combustion gases from furnaces and boilers.
G
Geothermal
A heat pump system that uses ground temperature for heating and cooling.
Grille
A decorative cover for supply or return air openings.
H
HSPF
Heating Seasonal Performance Factor - Measures heat pump heating efficiency.
Heat Pump
A system that provides both heating and cooling by reversing the refrigeration cycle.
Heat Exchanger
Component in furnaces that transfers heat from combustion to air without mixing gases.
HEPA
High-Efficiency Particulate Air - Filter that removes 99.97% of particles 0.3 microns or larger.
Humidistat
A device that measures and controls humidity levels.
HVAC
Heating, Ventilation, and Air Conditioning - The technology of indoor environmental comfort.
I
IAQ
Indoor Air Quality - The quality of air within and around buildings.
Inverter
Technology that varies compressor speed for improved efficiency and comfort.
L
Load Calculation
Manual J calculation to determine proper HVAC system size for a building.
Latent Heat
Heat energy required to change water from liquid to vapor (humidity removal).
Line Set
Copper tubes connecting indoor and outdoor units containing refrigerant.
M
MERV
Minimum Efficiency Reporting Value - Rating system for air filter effectiveness (1-20).
Mini Split
Ductless heating and cooling system with individual room control.
Modulating
Equipment that adjusts output in small increments for precise comfort control.
Manual J
Industry standard calculation method for residential HVAC sizing.
N
NATE
North American Technician Excellence - Certification program for HVAC technicians.
P
Plenum
Large duct section attached to air handler where smaller ducts branch off.
PSI
Pounds per Square Inch - Pressure measurement for refrigerant and gas.
Programmable Thermostat
Thermostat that automatically adjusts temperature based on preset schedules.
R
R-Value
Thermal resistance rating of insulation materials.
Refrigerant
Chemical compound that absorbs and releases heat in the refrigeration cycle.
Return Air
Air drawn back to the HVAC system for reconditioning.
Reversing Valve
Component in heat pumps that reverses refrigerant flow for heating/cooling modes.
S
SEER
Seasonal Energy Efficiency Ratio - Cooling efficiency rating over an entire season.
SEER2
Updated SEER rating with new 2023 testing standards for more accurate real-world performance.
Static Pressure
Resistance to airflow in ductwork, measured in inches of water column.
Subcooling
Temperature difference between liquid refrigerant and its saturation temperature.
Superheat
Temperature increase of refrigerant vapor above its boiling point.
Split System
HVAC system with separate indoor and outdoor units.
T
Thermostat
Control device that maintains desired temperature by controlling HVAC operation.
Tonnage
Cooling capacity measurement - one ton equals 12,000 BTU/hour.
TXV
Thermostatic Expansion Valve - Regulates refrigerant flow to evaporator coil.
Two-Stage
Equipment with two operating levels for better efficiency and comfort.
U
U-Value
Thermal transmittance - inverse of R-value, lower is better for insulation.
V
Variable Speed
Motor or compressor that adjusts speed based on demand for optimal efficiency.
VRF
Variable Refrigerant Flow - Commercial system with precise zone control.
Ventilation
Process of exchanging indoor air with outdoor air for improved air quality.
Z
Zone Control
System allowing different areas to be heated/cooled independently.
Zoning
Dividing a building into areas with independent temperature control.
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