HVAC terms: What do they mean?

March 12, 2021

HVAC terms: What do they mean?

When you’re considering a new HVAC system, you’ll encounter an alphabet soup of terms. Like any industry, the heating and cooling industry uses a bevy of abbreviations that aren’t familiar to the everyday consumer.

Let’s break them down so you can decipher the information out there about furnaces, heat pumps, cooling units, and other HVAC products once you start your research.

BTU (British Thermal Unit)

Let’s start with the most basic abbreviation. The British thermal unit (BTU) is the standard unit of energy. It’s the amount of energy it takes to raise the heat of one pound of water one degree Fahrenheit at sea level.


Tonnage refers to the cooling capacity of a cooling system. Systems specialists in our industry use it to determine what size system you need to adequately cool your home. A ton equals 12,000 BTUs so, for instance, a 3-ton system can provide 36,000 tons of cooling energy. Your specialist will determine tonnage based on the age of your home, square footage, the amount of insulation you have, and other factors.

Fun fact! The term “tonnage” originated with the earliest indoor cooling systems. Before modern cooling systems were invented, people blew fans over blocks of ice to cool down homes, movie theaters, and other businesses. A “ton” came to be known as the amount of energy it took to melt one ton of ice.

CFM (Cubic Feet Per Minute)

The cubic feet per minute (CFM) measures airflow. Specifically, it indicates the volume of air for each minute it moves. To work properly, a system needs at least 400 CFM per ton to work efficiently.

COP (Coefficient Of Performance) and  EER (Energy Efficiency Ratio)

COP and EER are about an air conditioning or heat pump system’s efficiency. They signal the relationship between the ratio of heating or cooling a system provides and the amount of electricity it takes to create that energy. In general, the higher the COP and EER rating, the more efficient that system is.

AFUE (Annual Fuel Utilization Efficiency)

Annual Fuel Utilization Efficiency (AFUE) indicates the amount of heat energy lost. If a system has an AFUE of 80, 20% of the heat energy it produces is going up the flu. So, the higher the AFUE, the more efficient it is.


Heating Seasonal Performance Factor (HSPF) and Seasonal Energy Efficiency Ratio (SEER) are measurements meant to indicate the efficiency of your heat pump. The point of these ratings is to give you an idea of how efficient a heat pump is over an entire season for both heat (HSPF) and cooling (SEER), rather than a day-to-day or moment-to-moment experience.

Though these are standardized measurements, we feel they don’t always equate to the real-world experience of consumers because outside factors can influence the actual efficiency, once it’s installed in your home.

When a systems expert takes a look at your space, they can help clarify these ratings as they apply to your specific situation and give you an idea about how you can expect them to perform in your space.

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