For many of us, our HVAC systems are a crucial part of our home comfort. While you may be aware that HVAC is an acronym for Heating, Ventilation, and Air Conditioning, you may struggle with industry terms. This can make it difficult to communicate with HVAC technicians or feel more confident discussing problems and issues. So, here we’ll explore the HVAC terms you should know.


Most of us are aware of the term efficiency. In our environmentally aware world, the term efficiency is used for practically everything, from kitchen appliances to vehicles. What you may not know is how efficiency is gauged and measured in HVAC systems.

In 1992, minimum efficiency requirements for all HVAC equipment was established by the Federal Government. So, if your current HVAC equipment was installed before this date, it is likely to be highly inefficient using today’s standards.

The efficiency rating is important to understand, as installing a new unit could save you a great deal in the long term. Although there is an initial installation cost, if the unit is far more efficient, it will use less energy, lowering your bills in the weeks, months, and years after installation.

Efficiency Terms:

Unfortunately, efficiency is not so simple to quantify. There are a number of efficiency terms that can seem confusing to the uninitiated. So, we’ll explore these in a little more detail here.

  • DOE: This is an acronym for the Department of Energy. This is the federal agency with the responsibility to set industry efficiency standards. They are also in charge of monitoring energy consumption.
  • AFUE: The Annual Fuel Utilization Efficiency or AFUE is a measure of furnace heating efficiency. It is represented as a percentage, and the higher the percentage, the more efficient the furnace. The current minimum rating for furnaces set by the government is 78%.
  • SEER: Seasonal Energy Efficiency Ratio or SEER is the measurement for the cooling efficiency of AC products. The higher the rating, the greater the efficiency. The current government minimum SEER rating is 10.
  • HSPF: This stands for Heating Seasonal Performance Factor, and it is a measurement of the Heat Pump efficiency. The higher the rating, the more efficient the heat pump will be at heating your home. There is currently no legislated minimum HSPF rating.

HVAC Terms:

Many people can feel a little overwhelmed when the time for an annual HVAC service rolls around, or they need to call in a repair technician. This is usually due to the terminology being unfamiliar. Fortunately, you can develop a little more confidence by learning about the following terms.

  • Air Handler: This is the part of central AC or heat pump systems responsible for moving the treated air through the ductwork. In some HVAC systems, the furnace handles this function.
  • Heat Source: This refers to a body of liquid or air from which heat will be collected. For example, in an air source heat pump, air outside the home is used as a heat source for the heating cycle.
  • Indoor Coils: This is the part of a central AC system or heat pump located inside the house. It acts as a heat transfer point for cooling or warming the indoor air.
  • Outdoor Coils: This is often referred to as the condenser unit and is the part of the system outside the home. It acts as a heat transfer point to collect heat from or dispel heat outdoors.
  • Single Package: This is a year round HVAC system that encases all of the components into one unit outside the property. This is typically used for commercial or rooftop applications.
  • Split System: This refers to a central AC system or heat pump with components inside and outside the building. This is the most common type of AC system installed in homes.
  • Supplementary Heat: This is an emergency or auxiliary heat that is provided when the temperature is below the balance point of the heat pump. This is usually in the form of electric resistance heat, but it can be oil or gas fired equipment.
  • Zone: Zones refer to the areas that the thermostat is controlling. This allows for greater flexibility, as you can have certain rooms warmer or cooler than others. In a typical two story home with a thermostat on each floor, there will be two zones, one on each floor.

Technical Terms:

Now, you’re a little more familiar with basic terms; we’ll get a little more technical.

  • Ton: This is a measurement of sizing for air conditioners and heat pumps. The typical size for a single family residence is two to five tons, and each ton is equal to 12,000 BTU. However, it is important to note that the actual capacity will not be constant, as it can change according to the indoor and outdoor temperatures. The published ton capacity rating is based on performance at the standard temperature levels of 80ºf inside and 95ºf outside.
  • Defrost Mode: During heat pump heating cycles, frost may accumulate on the outdoor coil. To maintain efficiency, the system is designed to automatically defrost and remove this frost. This typically takes just a few minutes before the system switches back to heating automatically. It is not unusual to see steam rising above the outdoor unit during this mode.
  • Balance Point: This is the outdoor temperature at which the exact output of a heat pump equals the heating needs inside the house. When below the balance point, it is necessary to use supplementary heat to maintain the desired indoor comfort levels.
  • Coefficient of Performance: Commonly referred to as COP, this is a ratio that is calculated by dividing the total heat capacity of the heat pump in BTUs by the total electric output x 3.412.
  • Energy Efficiency Ratio: The EER is calculated by dividing the cooling capacity by the power output.

While many of these HVAC terms can seem unfamiliar, getting to know them can help you feel a little less overwhelmed when discussing your system with a repair or servicing technician. Of course, most professional technicians are happy to explain any issues in further detail, so don’t be afraid to ask.