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Common HVAC Terms

Here is a glossary of terms associated with heating and cooling to help you understand the often foreign-feeling concepts and terms.


The Annual Fuel Utilization Efficiency is a way to measure a heating system’s efficiency in turning fuel into energy. A 90 percent AFUE rating means that 90 percent of the fuel that the system uses is converted into energy. 

Air handler

This is the part of a split heating and/or cooling system that is located indoors and circulates air.


The part of heating systems that heats water to provide steam or hot water for heating. The steam is distributed through the pipes to baseboards and radiators.


This stands for British Thermal Unit, which is a measurement of heat energy. When it comes to heating systems, the BTU number measures the heat output. For A/C systems, BTU measures the capacity of the cooling.

Central air conditioning

 Central A/C is a system where the air is cooled at a central location before being distributed throughout the home or office via ductwork.


In a central air conditioning split system, the condenser is the part of the unit that is located outdoors. The condenser’s job is to release the heat accumulated by the indoor part of the air conditioner.

Condensate line

 This keeps moisture from building up inside of the A/C unit. Moisture in a unit leads to mold, mildew, corrosion, and other damage to your home. The condensate line is essentially an exit path for moisture that is collected by the evaporator coil as air passes over it. The coil works to remove humidity from the air and turns it into water. The water drains into the condensate drain pain, goes in the drain line, travels down the drain pipe, and is eventually deposited outside the AC outdoor unit.

Ductless mini-split

These cooling systems have indoor and outdoor units but do not require ductwork. With ductless mini-splits, you eliminate the need for multiple air ducts and can create separate HVAC zones, each one with its own thermostat. This becomes beneficial in larger homes and office spaces, and other add-on areas that don’t have ductwork installed.


Ductwork is used to distribute the airflow from HVAC systems throughout a home or office. Air is sucked from throughout the home into the heater or AC unit where it is either heated or cooled before being pushed back through ducts into the living area.

Evaporative cooler

The evaporative cooler, also known as a swamp cooler, cools air through water evaporation. This cooling system works best in areas where humidity does not go above 60 percent, Southeastern parts of the U.S., for example. 

Evaporator coil

In a central air conditioning system, this lives indoors with the furnace or air handler. The evaporator coil holds the chilled refrigerant that is used to draw out the heat from the air in the building.


Furnaces are a home heating system type that is usually gas-powered. Air is forced through a series of ducts within a furnace. This process distributes heated and air-conditioned air throughout your home. Gas furnaces are the most popular type of heating system because the ductwork can be used by your A/C in the warmer months. 


HVAC stands for heating, ventilation, and air conditioning. This is the term generally used to describe home heating and cooling systems.

Heat pump

Heat pumps handle both heating and cooling by transferring heat between a home and the outdoors. They work best in moderate climates where temperatures don’t commonly dip below freezing.

Packaged system

These systems are also referred to as an all-in-one system. All parts of the system are in one outdoor unit that is usually installed on a roof or next to the home or office on a slab.


 Refrigerant is used in an A/C unit to absorb heat from indoor air.

R-22 refrigerant

This is called Freon. R-22 is not used much anymore and is in the process of being phased out in favor of refrigerant types that are more environmentally friendly.


Seasonal Energy Efficiency Ratio measures the efficiency of air conditioners. The higher the SEER rating, the more efficient a system is. 

Split System

These systems are the most commonly used type of residential HVAC. The split system has two main parts: indoor and outdoor.

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