Your air conditioner is a complex system that requires professional care and attention to keep it running efficiently and effectively. While you may wish to leave maintenance and repairs to the professionals, a little know how can be important. If you want to feel more confident understanding industry terms, we have produced a brief guide to the common air conditioner and heating terms.

AC Fan 

These types of fan are driven by an alternating current or AC motor to provide air movement in your heating, cooling and ventilation system.

Air Conditioner 

Air conditioners are appliances, systems or mechanisms that are designed to control humidity, temperature and the air quality in defined spaces.


The AHU or Air Handling Unit is an indoor component of heat pumps or air conditioners that is responsible for moving cooled or heated air around the ductwork inside the home.


British Thermal Unit or BTUs are a measurement of heat energy. A BTU is defined as the amount of energy needed to increase the temperature of one pound of water by one degree Fahrenheit. When shopping for heating equipment, the higher the BTU, the greater the system heating capacity.

Central Air Conditioning 

This type of system involves air being cooled at a central location. The cooled air is then distributed by fans through ductwork to various rooms or areas.


CFC or Chlorofluorocarbons are commonly used as a refrigerant. Unfortunately, CFCs are considered detrimental to the environment, so the manufacture and use of these compounds have been gradually phased out to be replaced with zero Ozone depleting compounds such as HFCs (hydrofluorocarbons).


Coils are mounted inside air handling units or ductwork to provide heat transfer to the air. The term “coil” in the context of air conditioning equipment is normally associated with a tube heat exchanger and fin using water or refrigerant as a heat transfer medium.


The compressor is a key component of any refrigerant system. It raises the pressure and temperature of the refrigerant to allow it to circulate through the closed loop system.


The condenser is a vital component to remove the superheat of compression to allow the refrigerant gas to be converted into a high pressure liquid.


This is the term used for the process of removing moisture from the air in a conditioned space to maintain the desired humidity level.


Ductwork is used in HVAC (heating, ventilation and air conditioning) to deliver and remove air. Ductwork typically includes provision for return air, supply air, and exhaust air.


The Energy Efficiency Ratio is a formula to calculate the efficiency of a window unit air conditioner or ground source heat pump. EER is a ratio of cooling capacity in BTUs to the power input in watts. The higher the rating, the greater the efficiency.

Evaporator Coil 

This part of your air conditioner or heat pump absorbs heat from the air inside your home. The evaporator coil is usually found inside the air handler of your air conditioner or attached to your furnace.


The fan coil unit is typically a chilled water device that consists of a heating and cooling oil, valves, a fan, and a local controller to form part of the larger HVAC systems used in commercial, industrial and residential buildings.

Gauge Pressure 

This reading is taken from a gauge that is normally zeroed at atmospheric pressure. This setting of 14.7 psi or one bar absolute allows pressure to be read as a negative if the conditions drop below atmospheric pressure.

Heat Pump 

Heat pumps are mechanical devices that absorb low grade heat from lower temperature locations, upgrading and transferring it to higher temperatures to heat a space to the desired comfort level. Heat pumps are available as air to air, water to water, air to water and ground to water.


This is the process of adding moisture into the air within a room or space.

Load Calculation 

This is the calculation used to determine how much heat is lost or gained by a house. This can include duct losses and internal gains from appliances and people. The load calculation is used to account for added heat transfer from the sun shining on windows, roofs and exterior walls and the capacity of the structure to store heat. This forms a significant part of the design process for HVAC systems.


The MERV or Minimum Efficiency Reporting Value rating is used as a method of ranking the efficiency of types of air filter. Each air filter has holes to allow particles and air to pass through. When the holes are smaller, it restricts the particles that are able to pass through. A filter with a higher MERV rating has smaller holes and greater filtration.

Natural Refrigerant 

Natural or non fluorochemical refrigerants exist naturally within the environment. This group of refrigerant includes carbon dioxide (R744), ammonia (R717) or hydrocarbons such as isobutene (R600a) or propane (R290). Since these products are naturally occurring, they provide an alternative to conventional fluorochemicals and are often used due to the low direct GWP and ODP potential. It should be noted that the commercial production of many natural refrigerant products is typically accomplished with man made synthesis.


This is the fluid used for heat transfer within refrigerant systems. Refrigerant absorbs heat at low pressure and temperatures, transferring it at high pressure and temperatures. Refrigerant can be produced from many materials including air or water.

Split Systems 

Split system air conditioners consist of two primary components; the outdoor condenser unit and the indoor unit. While any size of system could be defined as split system, this term typically refers to smaller equipment.

Static Pressure 

This is often overlooked,  but static pressure can have a massive impact on the effectiveness and efficiency of your system. In simple terms, static pressure is any resistance to airflow within HVAC ductwork and system components.


This is a device that regulates temperature automatically or that activates equipment when the temperature hits a specified point.

These common terms will help you to understand what your HVAC technician is saying when assessing your system, but don’t forget that a good technician will be happy to answer any remaining queries or questions.