Key HVAC Terminology You Need to Know

hvac workerAs fluctuating temperatures become the new seasonal norm, homeowners begin to seek optimal HVAC (heating, ventilation and air conditioning) performance. Many may be surprised to learn their HVAC system should be inspected yearly, as HVAC maintenance is a crucial to-do in order to maintain efficient heating and cooling, prevent costly breakdowns and ensure consistent indoor comfort.

Navigating the HVAC industry can be perplexing, with its unfamiliar acronyms and specialized jargon. When you better understand HVAC-industry key words, you may make more confident purchasing decisions as well as communicate better with contractors.

The following is a list of commonly used HVAC-industry terms that to know.


Refrigerant is the liquid used to absorb and transfer heat from one part of the home comfort system to another. It’s important that refrigerant levels be properly maintained — neither too high nor too low.

Newer to use within the U.S. air conditioning sector, A2L is a group of refrigerants with a lower toxicity and flammability rating compared to A2 or A3 refrigerants. A2Ls have emerged as a replacement for older, high-impact refrigerants. Experts anticipate that A2L refrigerants will be required in 2025.

Air Handler

An air handler is the part of an HVAC system that circulates conditioned air throughout the home.


A furnace heats the inside of a home. It uses natural or liquified petroleum (LP) gas instead of refrigerant to heat the air inside the home.

BTU (British Thermal Unit)

BTUs indicate the amount of heat required to raise or lower the temperature of one pound of water by one degree Fahrenheit. Understanding BTU allows you to determine the heating or cooling capacity required to maintain a comfortable indoor temperature, ensuring the HVAC system is adequately sized for the living space.

Condensing Unit

Condensing units are found outside of the home. They are connected to the indoor unit, either an air conditioner or heat pump, with tubing to carry refrigerant, which is used to transfer heat. To cool your home, a condenser removes heat from indoor air. To heat your home, it brings natural warmth from outdoor air inside your home. A heat pump can also heat your home.


The higher the following ratings, the more efficient the unit:

  • EER2: The updated metric for energy efficiency ratio, formerly known as EER. The ratio of the cooling capacity of the air conditioner or heat pump in BTUs per hour to the total electrical input in watts. This measure is determined by comparing test units to the Air Conditioning and Refrigeration Institute (AHRI) specifications.
  • HSPF2: The updated metric for heating seasonal performance factor, formerly known as HSPF. It measures the efficiency of the heating portion of a heat pump.
  • SEER2: The updated metric for seasonal energy efficiency rating, formerly known as SEER. It is used to express the efficiency of an air conditioner or a heat pump in cooling mode. Similar to miles per gallon in a car, a higher SEER2 number indicates a more efficient unit.

Residential Packaged Unit

This is the cabinet where all heating and cooling components are located. The unit is installed either beside or on top of a home or business.

Split System

A split system is a home comfort system that uses an indoor and an outdoor component to deliver comfortable air to a living environment. This may involve a combination of elements such as a condensing unit located outside, air handler or furnace positioned indoors. In the case of a system incorporating a gas furnace, an evaporator coil inside the home is also utilized.

Stage Systems

These are HVAC systems designed with various operational stages, including single-stage (on/off), two-stage (two levels of heating or cooling capacity) or multistage (variable speed) configurations, enabling them to adjust heating or cooling output to meet comfort preferences while maximizing energy efficiency in diverse conditions.

Zone or Zoning

A home may be divided into several different areas, or zones, to better control the temperature. The process of dividing a home into different zones is called zoning.

With basic terminology top of mind, you can seek better optimization of HVAC system performance. Ask questions and gain clarity from trusted contractors. Effective communication with these experts holds the key to precise assessments, improved energy efficiency and adherence to safety and compliance standards.

Rheem, an innovator in manufacturing HVAC equipment, offers Rheem Pro Partners who are contractors well-equipped with resources to provide professional advice and assistance to homeowners throughout the process. Trusted HVAC contractors, like Pro Partners, can ensure customers find the perfect solution for home comfort needs. Additionally, a well-trained contractor should be able to update and inform about cost savings, rebates and energy efficiencies.

It’s not merely about terminology; it’s about increasing your confidence as you create a comfortable, efficient and safe home environment for your family.