Know Your HVAC Vocabulary

By Four Seasons Heating, Air Conditioning, Plumbing & Electric - June 6, 2018

The HVAC industry is stuffed full of jargon and vocabulary unfamiliar to the average consumer. Without an understanding of key terms like AFUE and SEER, it is nearly impossible to make an educated, informed furnace or air conditioner purchase. To help you learn the lingo and gain a little insight into the industry we love, here is a thorough list of HVAC terms and definitions.

A.F.U.E. Or Annual Fuel Utilization Efficiency

Listed as a percentage, this is a direct ratio of fuel pumped into the furnace and usable heat created from the fuel. For example, the SLP98V is 98% AFUE. Meaning, for every 100 BTUs of fuel the furnace uses 98 BTUs of heat enters your home. Clearly, the higher the AFUE, the better.

Balance Point

Signifies an outdoor temperature generally between 30-45°F. At this temperature, the heat pump’s output equals the heating needs of the home. When dropping below the balancing point, additional electric resistance heating is required to establish and maintain indoor comfort.

Btu or British Thermal Unit

Equates to the amount of heat and energy required to raise the temperature of one pound of water one degree Fahrenheit.
Ex. a 10,000 BTU furnace is capable of creating 10,000 BTUs of heat per hour.

Cfm Cubic Feet per Minute

A standard measurement of airflow. It measures the amount of cubic feet that can be filled, heated, or cooled in one minute.


The heating or cooling capabilities of a unit. Normally, this is displayed in BTUs.


The compressor pumps the refrigerant through the coils in the outdoor segments of the air conditioner or heat pump. It pumps the refrigerant at a speed and in quantities sufficient to cool the home.

Condenser/Evaporator Coil

Located in the outdoor segment, the condenser coil houses the refrigerant that will change from liquid to gas and cool the air through evaporative cooling.


In air ducts, these vents restrict or permit airflow to regulate the air distribution to certain rooms.

Downflow Furnace

This kind of furnace is designed to intake air through the top and expel heated air through the bottom.


Metal pipes that distribute air throughout your home.

EER or Energy Efficiency Ratio

The energy efficiency ratio of a cooling system. It indicates how effectively the air conditioner will operate at a specific temperature (usually at 95°). The higher the rating, the more efficient the system.

Heat Exchanger

The in-between device that transfers the heat energy from the combusting fuel to the air that will distribute the heat.

Heat Pump

An electric unit that is capable of both heating and cooling a home by reversing the flow of the refrigerant change of state (gas to liquid, liquid to gas). Heat pumps extract heat from the air even in cold weather. They are generally used on more mild days because they operate with peak efficiency between 40 and 90° F.


This device produces water vapor in conjunction with your furnace to improve comfort and regulate humidity.


A term to describe the amount of moisture in the air. Air Conditioners and dehumidifiers work to lower humidity.

HSPF or Heating Seasonal Performance Factor

The important thing to note is that a higher score on the HSPF scale yields a more efficient Heat Pump. Specifically, HSPF measures a heat pumps estimated heating output for the Spring and Fall.

HVAC or Heating, Ventilation, and Air Conditioning

Generally used as an abbreviation for the entire industry and list of services offered by Four Seasons.
ex. Four Seasons is the Midwest’s largest HVAC company.

M.E.R.V. or Minimum Efficiency Reporting Value

Stands for the Minimum Efficiency Reporting Value and measures the efficiency of a filter or air cleaner. It ranges from 1 to 20 with the latter being the stronger filter able to capture particles down to .3 microns in size.

Package System

A heating or cooling system wherein all the components are located within one unit. The opposite of a split system.


A substance housed in the evaporator coils which changes from gas to liquid to create a cooling effect.

Refrigerant Lines

These two copper lines connect the outdoor unit to the indoor unit in a split system.


R-value is a measurement of the effectiveness of your insulation. Depending on where you live, certain areas are recommended to have specific levels of insulation to keep their energy costs low. In the Chicago and Northwest Indiana area, it is recommended to have an R-Value between R-38 and R-60 in your attic.

S.E.E.R. or Seasonal Energy Efficiency Ratio

SEER stands for Seasonal Energy Efficient Rating. It is calculated by dividing the typical cooling output of an average season by the total energy input during the same amount of time. The important thing to understand about SEER ratings is that a higher rating equates to a more efficient system.

Split System

The most common cooling system design. It contains a cooling unit both inside and outside the home. The opposite of a package system.

Switchover Valve

The mechanism reverses the flow of the refrigerant to change from heating to cooling mode and back again.


This is your control station for your heating and cooling system. It allows you to set the temperature in the home, and once set, your heating and cooling system will automatically operate as needed to regulate the temperature. In addition, some thermostats are programmable which allow you to automatically set the temperature for different times and days of the week.


A Ton is a unit of measurement to reflect cooling capacity.
e.x. 1 ton = 12,000 BTUs per hour.

Upflow Furnace

This furnace design intakes air from the bottom and expels hot air from the top of the unit.

Ultraviolet Light or U.V. Light

Also known as a UV Lamp, a UV light is an air purifier that utilizes ultra-violet light to kill pathogens. This is normally attached to the evaporator coil or installed in the duct work near the furnace.


To segment the home into areas or zones. Zoning then allows the furnace and air conditioner to target heating and cooling to respective zones.

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