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About 49% of U.S. Households use natural gas to heat their homes.

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A heating, ventilation, and air conditioning unit is also known as an HVAC system. The unit controls the temperature, humidity, and air filtering within a home or business and requires proper installation and zoning — this is where HVAC vocational technicians come into play. When you know the ins and outs of an HVAC system, you can provide people with a comfortable and clean environment.

Types of HVAC Systems

Many people question the difference between an HVAC system and an air conditioner, and may not know the different types of units available for residential and commercial areas. Several types of systems exist along with those that have energy-efficient ratings. Here is a quick glance at five of the most common HVAC terms.

Heating Systems

These provide hot air to homes by using furnaces. The systems burn natural gas or propane and distribute the converted heat through a series of ductwork. About 49 percent of U.S. households use natural gas to heat their homes, and conventional heating systems can achieve up to 98 percent efficiencies by converting almost all the fuel to heat. Electric furnaces and radiant floors are two more types of heating units, along with boilers that use gas or oil. It’s important to know the Annual Fuel Utilization Efficiency of each, too.

Cooling Systems

Also referred to as air conditioning units, they come in different types to best suit a household’s requirements. Depending on where people live, some may opt for central air, while other may prefer window units or mini-splits. Efficient air conditioners use about 30-50 percent less energy than they did 40 years ago. Air conditioners comprise a compressor, condenser, and evaporator to control the humidity of a home and provide cold air.

Humidity Control

With humidifiers and dehumidifiers, you can regulate the humidity of a building as part of the heating and cooling systems. Homeowners can determine the amount of moisture in the air, which is especially useful for areas in dry or humid climates.

Zoned Systems

These are used to heat or cool individual rooms in your house. It can save a household energy and money because the system only heats or cools specific areas when necessary. The unit controls zone dampers inside the ductwork, which block the air flow to different rooms.

Single and Multi-Stage

A single-stage HVAC system is set to perform during the coldest and hottest days of the year. However, the unit also runs at full capacity when it may not have to. A multi-stage heating, ventilation, and air conditioning system can help save energy and money by fluctuating with different temperatures instead of working at max rates.

HVAC Certifications

If you are pursuing an education in HVAC, receiving certification is not legally required, but can boost your chances of landing the right job. While each state differs on what type of license you may need, the North American Technician Excellence certification is a reputable option. The NATE certification is nationally recognized and validates your HVAC knowledge.

Other certifications include the HVAC Excellence and the EPA 608.

HVAC Terminology

Terminology for the HVAC industry is vital to understanding the overall process and different elements within each system. Refer to the following list to help you learn about certain topics. Whether you want to pursue an HVAC technician program or want to know more general information about heating, cooling, and ventilation systems, this guide can increase your knowledge. Common terms for HVAC systems include the following.

HVAC Glossary of Terms

Alternating Current

An alternating current intermittently changes direction.

Annual Fuel Utilization Efficiency

AFUE percent is the measurement or rating that reveals a furnace’s efficiency when it converts fuel to energy. You find the percentage by dividing the ratio of the heat output by input. The higher the rate, the more efficient the furnace.

Air Cleaner or Filtration System

A unit that removes particles from the air, such as allergens and pollutants.

Air Conditioner

A unit outside that alters the temperature, quality of air, or humidity in your home.

Airflow Volume

The amount of air in a space measured in cubic feet per minute.

Air Handler

The indoor portion of your heating or cooling system with a filter, fan-blower and housing unit to move air through the ductwork in your home.

All-in-One System

Both an air conditioning and heating unit where all components are in one system outside the home. It’s also known as a single package.

All-in-One System: Both an air conditioning and heating unit where all components are in one system outside the home.

Balance Point

The temperature outside — between 30 and 45 degrees F — where the heat pump’s output is equal to the heating requirements of your home. If temperatures are below the balance point, the system will use supplementary resistance heat that’s usually electric.

British Thermal Unit

The measurement of heat needed to increase the temperature of one pound of water by one degree F when fuel burns. Regarding heating, the BTU measures the heat exhausted when fuel burns, and for a cooling system the BTU calculates the amount of heat extracted from your house.


A burner enables the burning of air and gas.

Burner Orifice

Opening of the burner where gas or fuel passes through before combustion.


Often referred to in BTUs, HVAC capacity is the output capability of a heating or cooling system.

Cubic Feet Per Minute

The measurement of airflow volume.

Charging a System

When you add more coolant or refrigerant to a unit.


The unit that circulates the refrigerant and maintains sufficient pressure to ensure it flows in the right quantities.


Condensation is when vapor turns into liquid as temperatures begin to decrease.

Condenser Coil

A series of tubes in the outdoor unit where heat emits from the refrigerant vapor and condenses into a liquid.

Condenser Fan

The fan removes any form of heat from the refrigerant as air passes over the condenser coil.


Where you can regulate the temperature of your home. It’s found on a wall inside your house that allows you to monitor and control the heating and cooling functions of the units.


When an HVAC system turns on and off.


A plate you can open and close to control the airflow in specific rooms in your home.


A unit that removes moisture and humidity from the air.


A grille that disperses air in a specific pattern located over an air supply duct.

Down Flow Furnace

Where the intake is on top of the furnace and the air discharge is at the bottom.

Drain Pan

When the refrigerant condenses into liquid form, the drain pan collects the water and transfers it to the drain line.


The pipes that transmit the hot or cold air through a house.

Evaporator Coil

A part of the heating or cooling system that transfers hot or cold air from the inside.


A vent that removes byproducts from combustion.


A heating system that works with an air conditioning unit or heat pump found indoors.


A strip of metal that connects two parts of an electrical circuit.

Heat Exchanger

A device where heat transfers to a cold surface.

Heat Gain

Heat created in an area.

Heat Loss

The amount of heat lost from an area.

Heat Transfer

When heat moves from one space to another.

Heating Coil

A heating coil performs as a heat source.

Heat Pump

A pump that allows an air conditioning unit to alternate between cooling in the summer and heating in the winter.

Heat Source

Where heat collects for the heating cycle.

Heating Seasonal Performance Factor

A measurement that calculates a heat pump’s efficiency throughout a season. The higher the HSPF, the higher the pump’s efficiency.

HEPA Filter

A High-Efficiency Particulate Absorbing filter that traps particles in the air.


A unit that increases the amount of moisture in the dry air during winter and hot climates.


A device that turns the humidifier on and off and measures humidity.


An acronym that refers to Heating, Ventilation and Air Conditioning.

Hybrid Comfort System

A hybrid system allows you to choose from two different fuel sources. It combines a gas furnace with an electric heat pump.

Hybrid Comfort System: A hybrid system allows you to choose from two different fuel sources. It combines a gas furnace with an electric heat pump.

Indoor and Outdoor System

An air conditioner is often located outside your home, and a furnace unit is inside.


When temperatures rise to the point of combustion.

Indoor Coil

An indoor coil attaches to your furnace air handlers. It draws out heat and moisture, resulting in cool and conditioned air.

Load Calculation

Completed by an HVAC technician, the analysis will help determine which system is best based on the energy requirements of your home.

Latent Heat

During a constant temperature process, energy is released or absorbed by the system.


A type of material that traps dust, bacteria, mildew, or dirt.


An opening.

Matched System

For your heating and cooling systems to perform at optimum levels for longer periods of time, a matched system is where all the components are equal in capacity and efficiency.

Modulating Heating

Adjusts and changes to the temperature in your house to provide better fuel efficiency and comfort.


The North American Technician Excellence is a certification program for HVAC technicians and is the only one recognized by the industry.

Outdoor Coil

Changes the refrigerant from a vapor to a liquid as it dissipates heat.

Outdoor Unit

As part of a central air conditioning or heating system, the outdoor unit transfers heat or cold air to the outside.

Packaged System

An air conditioning and/or a heating unit where all components are in one cabinet.


Pounds per square inch.


Used in cooling systems, refrigerant is a substance that creates a cooling effect.

Reciprocating Compressor

A piston compresses the refrigerant in a cooling system.


SEER stands for Seasonal Energy Efficiency Ratio. It measures an air conditioner’s or heat pump’s efficiency to cool. The higher the ratio, the more efficient the system.

SEER stands for Seasonal Energy Efficiency Ratio. It measures an air conditioner’s or heat pump’s efficiency to cool. The higher the ratio, the more efficient the system.

Sensible Heat

When heat is added or removed from a room, causing the temperature to fluctuate.


Seasonal Extreme Environmental Test tests about five years of operation under harsh conditions into 16 weeks.

Split System

A split system is where the components of an air conditioning and furnace unit are outside and inside your home.

Supplementary Heat

The emergency heat used when temperatures are below the balance point.


A temperature-controlled device you can monitor and determine the temperature you want to set. It’s usually found on a wall inside.


Measures the cooling capacity.

Two-Stage Heating and Cooling

Two-stage works at an energy-saving speed to be more efficient.

Up-Flow Furnace

A furnace that releases air through the top and pulls it in from the bottom.


The area where the pressure is below the standard pressure.


Electrical currents pushed along wires.

Variable-Speed Monitor

A variable-speed motor works with your thermostat to change speed depending on the heating and cooling requirements of your home. The fan reduces temperature variances and increases dehumidification.


A unit of electrical power.

Wet Bulb Thermometer

Measures the relative humidity.


When space in a home is divided into different regions to control the temperature from the heating and cooling units better.

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