HVAC technician working on an AC unit outside
HVAC/IAQ Glossary Common HVAC and Indoor Air Quality Terms

HVAC/IAQ Glossary

Search the glossary for the term you are looking for by entering your term in the below box and pressing enter.

  • General HVAC

    • Air Conditioner: A piece of equipment designed to control air temperature, air flow, and relative humidity in a room or space.
    • Air Cooled System: A system in which the condensing medium is air and uses refrigerant such as R-22 or R-410A. For air conditioning, any heat from inside is transferred to the outside and for the heat pump, air is drawn from outside and used to heat indoor air.
    • Air Handling Unit (or Air Handler): The part in a central air conditioning system that will move hot or cold air through the ducts in a home, but does not include said ductwork. This part typically includes a blower, dampers, and other pieces that help with the air flower and is usually located inside.
    • Blower: Equipment that moves air through a system, such as air handling unit, air handler, or furnace.
    • Charge: The quantity of refrigerant housed in a system.
    • Closed System: These systems cool water or refrigerant inside the tubes and do not transfer heat from inside a building to the outside. These systems are behind valves.
    • Coil (Indoor Coil): A piece of equipment that lets heat transfer back and forth from the refrigerant to the air when it is installed in an air handling unit. An indoor coil is often two rectangular surfaces that connect at the top and will open near the bottom. The indoor coils can look like the letter “A”, “N”, or “H” from the side or like the radiator in a car.
    • Compressor: A piece of equipment that distributes vapor refrigerant through the system, going from the indoor evaporator to the outdoor condenser and back again.
    • Condenser Coil: A collection of tubes that are filled with gas, or vapor, refrigerant and will carry heat from your home and move it outdoors, which allows the refrigerant to liquefy or condense and then the process will start again.
    • Condensing Unit: A piece of equipment that will condense a substance into a liquid state from a gaseous state. This generally occurs by cooling the gas. The latent heat will transfer to the condenser coolant.
    • Dual Fuel System: An energy efficient heating solution that has both a furnace and heat pump. The heat pump is used for basic heating needs and the furnace is used when high levels of heat are needed.
    • Duct: A closed chamber or pipe that is made of sheet metal or fiberglass. They handle the air flow from an air handling unit to the room or space being conditioned.
    • Ductless Mini-Split: An air conditioning system where the outdoor condenser is connected to the interior air handlers. This type of system does not use ducts at all to transfer air. These are good options for additions on your house because they typically are only made to cool one room at a time.
    • EER (Energy Efficiency Ratio): A ratio that will determine how energy efficient an air conditioner is. If an air conditioner has a higher EER rating, the unit is more efficient. EER ratings are typically lower than SEER ratings because SEER ratings are adjusted seasonally and EER are determined by a fixed ambient temperature.
    • Efficiency: The amount of energy that is used to complete a cycle. Efficiency is measured by either Seasonal Energy Efficiency Ratio (SEER) or by Energy Efficiency Ratio (EER). If the rating is high, your system is more efficient and the lower your energy consumption typically will be.
    • Evaporator Coil: Tubes that are filled with a liquid refrigerant and absorbs heat from room air at the same time the liquid refrigerant is evaporated into vapor.
    • Fresh Air Intake: The opening in a system where outdoor air is drawn in.
    • Furnace: Air distribution system that will add heat to air by burning fuel or move cool air for air conditioning.
    • Heat Pump: A system that has a reversing value that can switch from heating in the winter to cooling in the summer.
    • HSPF: Heating Seasonal Performance Factor that measures the efficiency of air source heat pumps. Higher numbers mean the heat pump is more efficient.
    • Humidity: The amount of moisture in the air.
    • HVAC: Heating, Ventilation, and Air Conditioning.
    • Load Calculation: A measurement that allows you to figure out the proper size HVAC equipment that should be installed by measuring heat gain and loss within a structure.
    • Payback Analysis: A way to determine the number of months it will take before you start to see energy cost savings each month and that will offset the purchase price.
    • R-22: A type of HCFC refrigerant that is typically used in residential air conditioning systems. Often referred to by its brand name, such as Freon®. This refrigerant is no longer being produced because it has ozone depleting properties and has higher global warming potential (GWP).
    • R-410A: A refrigerant that is replacing R-22 because it is a non-ozone depleting refrigerant. It performs at a higher pressure and required different equipment than R-22.
    • Refrigerant: A vapor that is used in many air conditioning systems that changes from a gas or vapor to a liquid and then back again to a vapor during the heating and cooling process. Also used to produce a heat transfer effect when the pressure of a refrigerant is changed. These are typically closed systems.
    • Register: A piece of equipment that will cover the end or opening of an air duct, generally a grille or damper.
    • Relative Humidity: A percentage that consists of the amount of moisture in the air related to the amount of moisture that could be in the air at the current temperature.
    • Return Air: Air that has been circulated through a room and is drawn back into the heating unit.
    • Room Air Conditioner (Window Unit): An air conditioner that is generally installed in a window and is a standalone air conditioning system. These systems only cool where they are installed and are less expensive to operate, but not as efficient as central air conditioning.
    • SEER: SEER is the abbreviation for Seasonal Energy Efficiency Ratio, which is a rating of the efficiency of an air conditioning system throughout one season. This includes both the hottest and coolest days. Higher SEER ratings mean the system is efficient.
    • Split System: A system where a compressor and condensing unit is installed outdoors and the air-handler is installed indoors. Split systems are the most common in the residential space.
    • System: Refers to the parts of a piece of equipment that perform an HVAC function.
    • Tonnage: How the cooling capacity of an air conditioning system is measured. It will take one ton of cooling to melt a one ton block of ice in 24 hours.
    • Zoning: Different sections in a home or building that are controlled separately through your heating or cooling system. These zones can be controlled separately or by opening and closing ducts or vents in each room in each zone.

    Indoor Air Quality

    • Air Filter: A filter in your HVAC system that is designed to filter out dust, pollen, and other particles from the air.
    • Carbon monoxide: A gas that is colorless and odorless and is toxic and flammable. It can be produced by fuels such as gas, coal, or oil.
    • HEPA Filter: High Efficiency Particulate Air filter that removes pollen, mold, dust, and more from the air.
    • Indoor Air Quality (IAQ): The air quality as it related to the health and comfort of occupants within and around buildings.
    • Radon: A gas that occurs naturally and can cause lung cancer. You are unable to see or smell radon and can only determine its presence by testing.
    • Ultraviolet light: Present in sunlight, this is a form of electromagnetic radiation present in sunlight.
    • UV Sterilization: A type of sterilization that will disinfect the air as it is cycling through your return ducts.
  • HVAC/IAQ & Plumbing Glossaries

    Our HVAC, Indoor Air Quality (IAQ), and Plumbing glossaries make looking up key terms and definitions a breeze. Simply click on the glossary below and you can search or filter by letter to find the word and definition you are looking for.