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HVAC Glossary & Common HVAC Terms

Have you had an HVAC technician out to your home and it seemed like they were talking in another language? Or maybe you got a few quotes on a new heating or cooling system, but you weren’t sure what some of the terms meant.

Well then this guide is for you.

Our goal here is to break down some of the most common words we use in the HVAC world but most people might not know. We’ll include some very basic terms, as well as more complicated ones.

When you know what a technician or sales person is talking about, rather than them talking above you, the power goes back to your hands. Our professional Simply the Best Heating & Cooling technicians are always eager and ready to answer any and all questions you may have, including breaking down everything they’re talking about to easy to understand terms.

ACH – Air Changes Per Hour

ACH refers to the number of times per hour a room is supplied or removed of air through mechanical and natural ventilation.

AC – Air Conditioner

This appliance or system is designed to remove heat as well as dehumidify a room or building. Room ACs are generally installed in windows or walls without ductwork. A central air conditioner uses fans and ducts to deliver cool air from a central unit outside to the rooms in your home.

AFUE – Annual Fuel Efficiency Ratio

AFUE measures the energy efficiency of your heating system whether it’s a furnace or boiler. It shows you how much of your total fuel usage is due to heating your home vs lost through exhaust. As an example, a furnace with an 80% AFUE rating means that 80% of the fuel is converted to heat and 20% is lost through exhaust. If your AFUE rating is below 80%, you should consider replacing your unit with a more energy-efficient model.

BTU – British Thermal Unit

One BTU is the amount of energy needed to raise the temperature of one pound of pure water by 1° Fahrenheit. A BTU is a measurement of energy used to indicate the rate of cooling, dehumidifying, or heating in an HVAC system. In easier terms, the higher the BTU rating, the greater the heating capacity of the system.

Carbon Monoxide – CO

Carbon monoxide is sometimes referred to as simply CO. It’s an odorless, colorless, tasteless, and very poisonous gas that’s produced when fuels like natural gas burn with insufficient air. A CO leak in your home can be extremely dangerous if not deadly.

Central Air Conditioning

A central AC system is a system in which air is cooled at a central location and distributed to and from multiple rooms via fans and ductwork.


Equipment that implements heat transfer to air when mounted inside an air handling unit or ductwork. It’s heated and/or cooled by electrical means or by circulating liquid steam within it.


An AC or Heat Pump compressor is the part of an outdoor unit that compresses and pumps refrigerant to cool the house to the desired temperature.

Condenser Coil

This component ejects or removes heat from the system in a basic refrigeration cycle. The condenser is the hot side of an AC or Heat Pump. Condenser coils are heat exchangers and can transfer heat to air. A central AC’s condenser coils are usually located in the outdoor air conditioner or heat pump unit.

Condensing Unit

These are the familiar temperature-control devices, with central HVAC and AC units, these are the devices outside that contain a system of coils, heat and cool spaces, fans, etc.


This is another word for a thermostat. This is a device that controls the operation of an HVAC system.

dB – Decibel

A decibel is a unit used to measure the relative intensity of a sound. As an example, the sound levels in a library are around 40 dB, normal conversations are around 50 to 60 dB, and a garbage truck can be as loud as 100 dB. The incredible Daikin FIT outdoor AC unit runs at about 56 dB.


Ductwork is specialized pipes or channels that allow airflow (including supply, return, and exhaust air) within a home. The most common type of ductwork is galvanized steel.


This is a piece of equipment that reduces the level of humidity from the air. It’s able to do this by cooling air to the point where water turns to liquid from vapor form.

Electronic Air Cleaner

Air cleaners, sometimes called ionizers or electronic air purifiers, use electrostatically charged filters to reduce the number of airborne contaminants in your home. As air passes through your heating and cooling system, the cleaner uses electrically charged filters to attract and trap harmful particles to prevent them from recirculating through your home.

Energy Star®

Energy Star® is a program by the U.S. Environmental Protection Agency (EPA) designed to help consumers and businesses save money by choosing energy-efficient products and technologies.

Evaporator Coil

Coil in the refrigeration cycle that absorbs or adds heat to the HVAC system. This is the cold side of an air conditioner or heat pump and is located inside the air handler or attached to the furnace.

Heat Pump

A compressor that cycles both hot and col air. It’s designed to move energy in the opposite direction of heat flow by absorbing heat from a cold space. Then it releases the heat to a warmer space.


This is the acronym for Heating, Ventilation, and Air Conditioning

MERV Rating

The Minimum Efficiency Reporting Value (MERV) rating is used to rank the efficiency of air filters. Every air filter has holes that allow air and particles to pass through. The smaller the holes, the fewer particles that can pass through. Higher MERV ratings mean smaller holes, which means more particles are getting filtered out.

NATE Certification

NATE stands for the North American Technician Excellence, they conduct independent testing verifying the real-world knowledge of HVAC technicians.


The substance that produces the cooling effect. This is used in most air conditioning and cooling systems. There are a few different types of Refrigerant: R12, R22, R410A and R134.

R12 and R22 have been phased out by the EPA and the Clean Air Act. R410A and R134 are much safer for the environment because they contain no chlorine.

SEER – Seasonal Energy Efficiency Ratio

The SEER measures the energy efficiency of an air conditioning system. You get the number by taking the Total Cooling Output Over the Cooling System / Total Electrical Energy Input Over the Cooling Season. To put it in easier terms, the SEER compares the total cooling of your AC or Heat Pump in BTUs with the energy output used within the same period. If that’s still confusing, just know that the higher the SEER rating on your air conditioner, the more energy efficient it is, thus lower energy costs.

Split System

This is a type of central HVAC system that gives you the ability to control the thermostat and temperature in different areas of the home. These systems don’t generally use ductwork but have small wall-mounts that deliver the heating and cooling to different rooms in the home. There’s usually one or more indoor units, an outdoor unit, and multiple thermostats.


A thermostat is a device that allows you to control the temperature of your HVAC system.

Give Simply the Best Heating & Cooling A Call

Hopefully this HVAC glossary and common HVAC terms guide was helpful for you. We’re always happy to help people understand different terms used in the HVAC industry that they might not be used to hearing. If are ever unsure of something we are explaining, or if you have a quote from another company and need some clarification, or another quote for that matter, give us a call today!