HVAC Lingo: Important Terms You Should Know

Enhance your knowledge of air conditioning service and HVAC systems. Familiarize yourself with central air units and important terms through experts at Sandium!

Updated on Oct 22, 2023
5 min read
HVAC Lingo: Important Terms You Should Know

HVAC systems are complicated. By having a better understanding of your HVAC system, you will be better able to communicate your needs with a technician in your Northern California home or business. It will also help you make better purchasing decisions. This is an extensive glossary of acronyms and terms associated with a typical HVAC system.

Air Conditioner (AC)

This is the mechanism or system that extracts heat and dehumidifies a building or room.

AFUE (Annual Fuel Efficiency Ratio)

AFUE measures your heating system’s energy efficiency. It tells how much energy is lost through exhaust versus the amount of fuel used for heating a home.

BTU (British Thermal Unit)

This measurement of energy is used for indicating the rate of heating, cooling, or dehumidifying in an HVAC system.


This device makes use of an absorption refrigeration or vapor-compression cycle for removing heat from liquid. Cooled liquid is made to flow through building pipes and pass through coils in fan-coil units, air handlers and other systems.


This equipment is mounted inside the ductwork or air handling unit and transfers heat to air. It is cooled or heated electrically by circulating steam of liquid within it.

Condenser Coil

This component is present in the refrigeration cycle and is responsible for removing or ejecting heat from the system. These are heat exchangers and can be used for transferring heat to a faraway sink, such as earth sink or air. It’s the hot side of the heat pump or air conditioner. The condenser coils in a residential HVAC system are generally located in the outdoor heat pump or air conditioning unit.


This device controls the operation of the HVAC system and may modulate the component’s set point subtly. These are automatic controllers and have user input, such as thermostat.


Ductwork refers to specialized channels or pipes for the airflow, including return air, supply air, and exhaust air.


They work by cooling air to a point where water turns into vapor form and is removed.


It is placed over the ductwork and separates air in different directions.

Evaporator Coil

This coil is used for absorbing heat from liquid or air. It’s the cold side of the heat pump or air conditioner and is attached to the furnace or located inside the air handler.


This is the facing on the duct opening and contains multiple parallel openings for delivering air to a ventilated space.

Heating Coil

This component conducts heat and allows electricity to act as fire.

Heat Pump

This is a type of compressor that cycles both cold and hot air. It moves thermal energy by absorbing heat from a space.

Heat Transfer

This is a vital step in cooling a space and occurs when heat moves from one place to another.

Packaged Unit or RTU (Rooftop Unit)

This is an air-handling unit that is defined as once-through or recirculating design. It is created for outdoor installation.

Plenum Space

This is an enclosed space inside a structure used for airflow.

SEER (Seasonal Energy Efficiency Ratio)

It uses BTUs for measuring the total cooling/heating of a heat pump or an air conditioner. Higher SEER means the system is more energy efficient.

Split System (Zoned)

You can control the temperature in different areas of your house with this. The unit makes use of small wall-mounts for delivering heating or cooling to different rooms.

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