Complete Guide to the Best HVAC Terminology

December 30, 2018

Do you know what an air handler is? How about bioaerosols? No? It’s okay. Here at Brennan Heating and Air Conditioning we not only know the ins and outs of your HVAC equipment, but also want to educate you on exactly what we are working with. So if you want to impress your HVAC technician next time they come to service your furnace, read on to learn the best HVAC terminology and how it relates to your system at home.

HVAC Terminology


Air Flow

Air flow relates to how much air is moved throughout your duct system.

Air Handler

The air handler’s main function is to effectively circulate conditioned air throughout your home. This is typically the indoor portion of the unit if you have a split system air conditioner. The air handler contains a blower, heating or cooling elements, filter racks or chambers, sound attenuators, and dampers.

Annualized Fuel Utilization Efficiency (AFUE)

The annualized fuel utilization efficiency, or AFUE, measures the furnace heating efficiency. The higher your AFUE, the more efficient your furnace will be.



Bioaerosols, or biological aerosols, are tiny airborne particles that are biological in nature. The problem with bioaerosols is that in large quantities indoors they can lead to respiratory problems and disease.

British Thermal Unit (BTU)

British Thermal Units, or BTUs, are a measurement of heat energy. One BTU is considered the amount of heat required to raise one pound of water by one degree Fahrenheit. When considering BTUs, the greater the BTU, the higher the heating capacity of the system.


Carbon monoxide (CO)

Carbon monoxide, or CO for short, is a colorless, odorless, tasteless, and poisonous gas. It is produced when fuels burn with insufficient air. When this gas leaks into your home, it can lead to serious health problems. To prevent this from happening make sure to get your equipment serviced regularly to make sure everything is working properly.

Central Air Conditioning

A system that cools air in a central location and then distributes that air to other rooms by fans and ductwork is known as central air condition, or central A/C.

Checking the Charge

Checking the charge is typically the process of finding out how much refrigerant is in your system. You may notice your service technician place his gauges on your system, these gauges measure the pressure of the refrigerant to see if you have the correct amount.


Coils are typically what increase or decrease the temperature via heat transfer. Most HVAC systems have two coils, the condenser coil and the evaporator coil.

Composite Fan Blades

Even in the harshest environments, composite fan blades are blades which are angled to improve operation and durability.


This is the part of your air conditioning unit that makes up most of the noise. It is part of the outside unit and is responsible for raising the temperature and pressure of the refrigerant.


A condenser, or A/C condenser, is the outdoor portion of a heat pump or air conditioner that either collects or releases heat.

Cubic feet per minute (CFM)

Cubic feet per minute, or CFM for short, typically refers to the measurement of air flow volume. This is determined by how many cubic feet of air pass by a stationary point in one minute.


Decibel (dB)

dB, or decibel, is used to measure the relative intensity of sound. This metric will help you to compare units based on the sound they produce.

Department of Energy (DOE)

The DOE, or Department of Energy, is a federal agency responsible for monitoring the consumption of energy sources. They also set industry efficiency standards for all heating and cooling units manufactured in the U.S.

Dual Fuel

A dual fuel system is one where an electric heat pump and a gas furnace are paired up in order to maximize the comfort and efficiency as it alternates between the two fuel sources.

Ductless Mini-Split

A ductless mini-split is a type of air conditioning, common in countries outside of the U.S. It is a split system heat pump usually with no ducts. Both the blower and evaporator coil are located in the head which is typically mounted on a wall or ceiling of the room it is trying to cool.


Ductwork is essentially a system of ducts that work to move air from HVAC equipment throughout your home. They are often metal or synthetic tubes that when properly installed and maintained will help indoor air quality and home comfort.


Electronic Air Cleaner

Electronic air cleaners are responsible for reducing the number of airborne contaminants in your home. They can also be referred as ionizers or electronic air purifiers. This component of your home comfort system uses electrically charged filters to attract and trap harmful particles as air passes through your system. This prevents those particles from recirculation throughout your home.

Energy Efficiency Ratio (EER)

The energy efficiency ratio, or EER, is the ratio of cooling capacity to the power input. The more efficient you want your air conditioner, the higher EER rating you should look for.


ENERGY STAR® is an U.S. Environmental Protection Agency program designed to help consumers and businesses choose energy-efficient products and technologies. If you see heating, ventilation, or air-conditioning equipment with the ENERGY STAR® logo on it, it either meets or exceeds the federal guidelines for energy-efficient performance.

Environmental Protection Agency (EPA)

The Environmental Protection Agency, or EPA, is a U.S. federal agency that develops and enforces federal environmental regulations. The EPA also oversees the Energy Star® program.

Evaporator Coil

An evaporator coil is part of an air conditioning system or heat pump. This coil absorbs the heat from the air inside your home and is located inside the air handler or attached to the furnace.


Gas Furnaces

One of the most common pieces of HVAC equipment, a gas furnace converts natural gas or propane into high-temperature heat for the home.


Heat Exchanger

This heating component is located in the furnace and it transfers heat to the surrounding air, which is then moved throughout the home.

Heat Pump

A heat pump is a piece of HVAC equipment that heats or cools a home by moving heat. During the summer, the heat pump removes heat from the home and releases it outdoors. During the winter, the heat pump draws in heat from outside and circulates it throughout the home’s air ducts.

Heating Seasonal Performance Factor (HSPF)

The heating seasonal performance factor, or HSPF, is the heating efficiency rating for heat pumps. If you would like a higher efficiency heat pump, look for a high HSPF rating.

Horizontal Flow

Most common in attic or crawl space installations, the horizontal flow describes an air handler or furnace positioned on its side. This piece of equipment circulates air in one end and out the other.


This device increases moisture to indoor air in a single room or throughout an entire house. It is often that the fan in your furnace or air handler will be used to blow the humidified air throughout the ductwork, but they can also work independently to maintain humidity levels even when the furnace or air handler isn’t operating.


HVAC stands for heating, ventilation, and air conditioning.

HVAC Damper

Also known as a duct damper, an HVAC damper is a movable plate, located in the ductwork, that regulates airflow and redirects it to specific areas of the home. These dampers are typically used in HVAC zoning systems.

HVAC Zoning System

Also known as zoned HVAC, an HVAC zoning system uses dampers in the ductwork to regulate and redirect air to specific areas of the home. This allows for customized temperature zones throughout the home for increased comfort and efficiency.



iComfort®-enabled products are those that are designed to work with the iComfort® programmable thermostat.

Indoor Coil

See evaporator coil.

ISO 9000

ISO 9000 is a family of international standards for quality management and assurance.


Latent Heat

Latent heat is essentially the heat you have to remove from the air to remove the moisture.

Line Set

The line set is the two refrigerant lines that connect the evaporator coil and condensing unit. Of the two lines, the smaller, hotter, uninsulated copper tube is the liquid line, while the larger, colder, insulated tube is the suction line.


MERV Rating

MERV, or minimum efficiency reporting value, is a rating to rank the efficiency of air filters in HVAC systems. A higher MERV rating means that the holes in the filter are smaller so less particles are able to get through. A higher MERV rating can also lead to higher efficiency.


A micron is typically used to measure airborne particles such as dust, dander, mold, and viruses. It is a unit of measure equal to one millionth of a meter.


NATE Certification

NATE stands for North American Technician Excellence. This organization conducts testing to verify the real-world knowledge and application of HVAC technicians and installers.


Outdoor Coil

See condenser.


Packaged Units

Packaged units are heating and cooling systems packaged into one outdoor unit.


Tiny substances less than 100 microns in diameter are called particles.

Programmable Thermostat

While there are many kinds of thermostats out there, a programmable thermostat is one in which it has the ability to adjust the home heating or cooling equipment according to a pre-set schedule.


R-22 Refrigerant

R-22 refrigerant is the old standard for residential air conditioners. This type of refrigerant is now being phased out by the U.S. EPA and is often very expensive to replace.

R-410A Refrigerant

This type of refrigerant meets the U.S. EPA’s newest, most stringent environmental guidelines and is chlorine-free.


Refrigerant is a chemical that produces a cooling effect while it expands or vaporizes.

Refrigerant Lines

Refrigerant lines are two copper lines that connect the outdoor air conditioner or heat pump to the indoor evaporator coil.


The return is the side of the duct system that pulls air from the home into the air handler.

Reversing Valve

This part is responsible for the difference between an air conditioner and heat pump.


Scroll Compressor

This type of compressor is specially designed to work in a circular motion rather than an up-and-down piston action.

Seasonal Energy Efficiency Ratio (SEER)

The seasonal energy efficiency ratio is the energy efficiency rating for air conditioners. If you’re looking for a higher efficiency unit, look for a higher SEER.

Sensible Heat

Sensible heat is the heat you have to remove from the air to create a lower temperature.

Split System HVAC

A split system HVAC is a heating and cooling system that includes an indoor unit (air handler and evaporator coil), outdoor unit (condensing unit), and thermostat. Both the indoor and outdoor units are connected via refrigerant lines.



This is a device that measures indoor temperature and humidity levels. It also automatically adjusts your heating or cooling system to maintain desired levels.


This is a device that measures the indoor temperature. It also automatically adjusts your heating or cooling system to maintain desired levels.


Upflow Furnace

Typically used in basements, closets, and attics, an upflow furnace is an air handler or furnace that is installed in an upright position where the air circulates through the side or bottom and out through the top.


Variable Speed Motor

A variable speed motor is a motor that operates at a wide range of speeds to precisely control the distribution of heated and cooled air throughout the home.


This pieces of equipment replaces the stale, recirculated air inside your home with fresh, filtered outdoor air.

Are you looking to replace your existing HVAC system? Or maybe you’re looking to add one altogether? Contact your local heating and air conditioning professionals Brennan Heating & Air Conditioning!

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