Definitions

Explanation of terms used in the HVAC industry. Having an understanding of these terms can improve your knowledge when it comes to making an informed decision on a heating and air conditioning repair or installation.

A | B | C | D | E | F | H | L |M | N | O | P | R | S | T | U | V | Z

Accumulator – prevents liquids from entering the compressor and is installed in the suction line of an air conditioner.
Advanced Reciprocating Compressor – a highly efficient type of compressor that has a longer working life than an average compressor. They are better at compressing refrigerant and are very reliable.
AFUE – (Annual Fuel Utilization Efficiency) measures the efficiency of how energy is converted to heat. An AFUE of 90 means that 90% of the BTUs are being used to heat your home, while the other 10% is wasted as exhaust.
Air Balance – is a term that describes air distribution in a HVAC system. Balanced systems deliver the correct amount of air flow to all rooms in your house.
Air Conditioner – A mechanical device that controls the temperature, humidity, and purity of your home’s air.
Air Flow Volume – The cubic feet per minute of air your air conditioner moves throughout your home.
Air Handler – is used to move air through the HVAC system. Air handler’s are usually placed in the attic or a small compartment inside your home.

BTU – (BritishThermal Unit) are used in heating and cooling to measure how much heat is added to or extracted from your home. 1 BTU is the amount of energy needed to raise on pound of water by 1 degree Fahrenheit. One BTU is also roughly equal to the heat given off by a wooden kitchen match.

Capacity – the amount a heating or cooling system takes to heat or cool a given amount of space. For heating, this is usually expressed in BTUs. For cooling, it is measured in tons. There are 12,000 BTU’s in a ton of cooling.
Carbon Monoxide (CO) – an odorless, colorless and toxic gas that consists of one carbon atom and one oxygen atom. Low levels of exposure to CO can cause headaches, dizziness, disorientation, nausea and fatigue. High levels of exposure can be fatal.
Chiller – removes heat from refrigerant and cycles the cooled liquid through air handlers or coils that allow your home to be cooled.
Coil – transfers heat between the air and the refrigerant. HVAC systems usually have two types. Evaporator coils absorb heat from inside air to the refrigerant and condenser coils transfer the heat from the refrigerant to outside air.
Compressor – is a device inside your air conditioner that pressurizes the refrigerant in the system. The compressor also circulates the refrigerant through the system.
Condenser Coil – is a device inside an air conditioner that causes the coolant to change state from a gas to a liquid. This process gives off heat that was absorbed by the coolant and transfers it to the outside air. The condenser fan blows air across the coil to speed the rate of transfer. Liquid coolant is then cycled used for dehumidifying and cooling.
Condenser Fan – is the fan that moves air through the condenser coil.
Controller – an electronic device that controls the operation of the heating or air conditioning system. Controllers turn the system on and off based on feedback from the thermostat and other parts of the HVAC system.
Cycling – is when an air conditioner turns on, runs, then turns off again.

Damper – a device that is installed inside your home’s air ducts to control air flow by partially blocking or unblocking the duct.
Diffuser – evenly distributes air by separating it with vanes that are placed in the duct work.
Digital Thermostat – is an electronic thermostat that controls your home’s temperature. Digital thermostats can be either programmable or non–programmable. Programmable thermostats can allow you to set your homes temperatures throughout the day without manual intervention. Some Digital thermostats can be controlled remotely with a computer, tablet or smartphone.
Downflow Furnace – a type of furnace that pulls in cool air from the top, and blows warm air out of the bottom.
Drain Pan – is located under the evaporator coil in an air conditioning system. The drain pan catches water from condensation buildup.
Duct – delivers air flow throughout the home. Most central air conditioning systems have both supply and return ducts at a minimum. Ducts can be made from many different types of material such as galvanized steel, aluminum, polyurethane, fiberglass, and flexible plastic.
Ductwork – is a term that refers to the ducts in your HVAC system that deliver air throughout your house.

ECM – (Electronically Controlled Motor) is an efficient DC driven motor that can run at different speeds making it much more efficient than an AC motor.
Electronic Air Cleaner (EAC) – filters out large particles and contaminants from your home’s air. It then it removes small particles that have been ionized, including and bacteria and viruses.
Energy Star – is a designation given to air conditioners that have a high degree of efficiency and preform above the minimum government standards.
Evaporator Coil – part of a split–system air conditioner or heat pump located indoors. The evaporator coil cools and dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the air. The warmed refrigerant is then carried through a tube to the outdoor unit (condenser coil).
Expansion Valve – is a valve in your air conditioner that allows liquid refrigerant to expand into a gas and release it’s heat.

Fan Coil – an indoor component of a heat pump system, used in place of a furnace. It provides additional heating through electric elements on cold days when the heat pump cannot provide adequate heating.
Freon – a trademark used for a variety of nonflammable gaseous or liquid fluorinated hydrocarbons employed primarily as working fluids in refrigeration and air conditioning and as aerosol propellants.
Furnace – a device that adds heat to your home that is usually runs off natural gas or propane or is electrically powered.

Heat Pump – refers to a compressor that can change between producing hot or cold air and circulating it through your home.
Horizontal Flow – a type of furnace, installed on its “side,” that draws in air from one side, heats it and sends the warm air out the other side. Most often used for installations in attics or crawl spaces.
HSPF – (Heating Seasonal Performance Factor) is a measure of the heating efficiency of a heat pump. The higher the HSPF number, the more efficiently the heat pump heats your home.
Humidifier – a piece of equipment that adds water vapor to heated air as it moves out of the furnace. This adds necessary moisture to protect your furnishings and reduce static electricity. Humidity levels should range from 35–50%.
HVAC – term used for Heating, Ventilation, and Air Conditioning.

Load Estimate – calculations and research performed to determine that your HVAC system is sized correctly for your home. Energy load analysis takes into account the square footage of your home, window or door areas, insulation quality and local climate to determine the correct heating and cooling capacity needed by your air conditioner, heat pump or furnace.
Louver – a device that is similar to a damper that is made of small adjustable blades that are used to control air flow to rooms or zones inside your home.

Matched System – a heating and air conditioning system built with products that have been matched to perform at a certain efficiency levels when used according to manufacturer specifications.

Natural Gas – an energy rich fossil fuel that is highly combustible and is often used for residential or commercial heating.

Operating Cost – the cost of the energy it takes to operate your HVAC system dependent on it’s energy consumption.

Packaged Unit – an HVAC system that contains both the heating and cooling devices internally. They are usually installed on rooftops and are sometimes called rooftop units or RTUs.
Payback Analysis – measures the value of your home’s HVAC system against it’s efficiency. Payback analysis accounts for how much the system costs compared to energy costs that are saved. The number of years before monthly energy savings offset the purchase price are calculated.

R-22 Refrigerant – is an older type of refrigerant used in HVAC systems. R-22 is being phased out and replaced with a more safe refrigerant known as R410A.
R410A Refrigerant – a more environmentally safe refrigerant that contains only fluorine and does not deplete ozone like other refrigerants can. Sometimes also called Puron. EPA regulations mandate the phaseout of hydro chlorofluorocarbons (HCFCs) from new AC systems by January 1st of 2010. R-410A has become the refrigerant of choice for central air conditioning systems.
Refrigerant Lines – are copper lines inside an air conditioner that connect the compressor, expansion valve, evaporator, and condenser.
Return Air – is air that is drawn in through the intake and moved through the filter and into the evaporator coil to be cooled or heated.
Return Duct – is the duct that runs between the air filter and HVAC unit that return air flows through.

SEER – (Seasonal Energy Efficiency Ratio) is a measure of the cooling efficiency of your air conditioner or heat pump. It is calculated by taking the cooling output and dividing it by the total energy consumption for a fixed period of time. A higher SEER number means the system is more efficient at converting electricity into cooling power.
Setback Thermostat or Programmable Thermostat – a thermostat that can be programmed to automatically adjust temperature settings at different times of the day.
Scroll Compressor – a special designed compressor that works in a circular motion by using two intertwined scrolls to pressurize refrigerant. Scroll compressors are generally more efficient and reliable because they have fewer moving parts.
Split System – is an air conditioning system or heat pump that splits the hot side and cold side of the AC system. Usually the cooling section know as the evaporator coil is inside while the hot side referred to as the condenser coil is outside.
Subcooling – term that refers to liquid refrigerant that is colder than the temperature where it would boil and change to a gas.
Superheat – term that refers to how many degrees in temperature a vapor is above its boiling point when at a certain pressure.
Supply Duct – is the duct that heated or cooled air flows through from the HVAC system to the rooms in your home.

Thermal Zone – term that refers to spaces inside a building that have similar thermal loads
Thermostat – a device that can sense air temperature and sends a signal to the the HVAC system based off a set point controlled by the user to provide heating or cooling to the building.
Ton – is a unit of measurement used in air conditioning systems that is equal to 12,000 BTUs per hour.
Two–Stage Furnace / Air Conditioner – is a furnace or air conditioner that has both low and high heating or cooling capabilities. Two stage systems provide more even temperature distribution and are more quiet and reliable than their single stage counterparts.

Underfloor Air Distribution– a ventilation method where an air plenum is installed underneath a raised floor to distribute air throughout the established zone.
Upflow – a type of furnace that pulls in cool air from the bottom, and blows warm air out of the top.

Variable Air Volume – (VAV) an efficient system that varies the volume of air flow throughout the air conditioned space to meet the temperature demand.
Ventilator – a device that exchanges your home’s air for air conditioned air that has a desired temperature, humidity, and purity.

Zoning – a system that uses dampers to improve your homes efficiency by directing airflow to certain parts or “zones” of your home.