HVAC Glossary

A-Coil

A heat exchanger containing two diagonal coils that are connected together in a manner that resembles the letter "A"

AC or DC

Abbreviation for equipment capable of operating on alternating or direct current

AFUE

Annual Fuel Utilization Efficiency—a measure of a gas furnace’s efficiency in converting fuel to energy; the higher the rating, the more efficient the unit

Air Cleaner

A piece of machinery that removes unwanted particles from moving air

Air Conditioner

A system for controlling the humidity, ventilation, and temperature in a building or vehicle

Air Flow Volume

The amount of air the system circulates through your home, indicated in cubic feet per minute (cfm); correct airflow depends on the indoor unit, the ductwork, the outdoor unit, and even whether the filters are clean

Air Handler

The portion of the central air conditioning or heat pump system that moves cooled or heated air throughout a home’s ductwork; in some systems, a furnace will handle this function

ARI

Air Conditioning and Refrigeration Institute

ASHRAE

American Society of Heating, Refrigeration and Air Conditioning Engineer

BTU

British thermal unit—the standard of measurement used to gauge the amount of heat required to raise the temperature of one pound of water by one degree (Fahrenheit)

BTUh

British thermal units per hour—12,000 BTUh equals one ton of cooling

Burner

An instrument that uses fuel to support combustion

Burner (Sealed Combustion)

A burner that acquires all air for combustion from outside the heated space

Burner Orifice

The opening through which gas flows to the air/gas mixing chamber of the burner

Capacity

The ability of a heating or cooling system to cool or heat a given amount of space—for heating, this is usually expressed in BTU’s; for cooling, it is often given in tons

Celsius

The metric temperature scale in which water freezes at zero degrees and boils at 100 degrees, designated by the symbol "C;" to convert to Fahrenheit, multiply a Celsius temperature by 9, divide by 5, and add 32 (25 x 9 equals 225, divided by 5 equals 45, plus 32 equals 77 degrees Fahrenheit)

CFM

The abbreviation for cubic feet per minute, commonly used to measure the rate of air flow in an air conditioning system

Charge

Adding refrigerant to a system; refrigerant is contained in a sealed system or in the sensing bulb to a thermostatic expansion valve

Climatuff® Compressor

The Trane Climatuff® Compressor was the world’s first successful heat pump compressor and, still to this day, it’s the only compressor Trane uses in its residential systems. The Trane Climatuff® Compressor is well-known for its superior durability, high efficiency, and low noise levels.

ComfortR™ Airflow System

An exclusive feature of a high-efficiency home comfort system from Trane; this method of ramping airflow gives you greater humidity control when cooling and provides warmer air during heating start-up

ComfortR™Coil or Evaporator Coil

A Trane Comfort Coil is the other, less-visible half of your air conditioning system and is located inside your home in the indoor unit. It’s a tubing coil in which a volatile liquid evaporates and absorbs heat. This is where the refrigerant evaporates as it absorbs heat from the indoor air that passes over the coil. It serves as a "heat exchanger," moving heat into your home in the winter and away from your home in the summer.

Compressor

The pump that moves the refrigerant from the indoor evaporator to the outdoor condenser and back to the evaporator again; the compressor is often called "the heart of the system" because it circulates the refrigerant through the loop.

Condensate

Vapor that liquefies due to the lowering of its temperature to the saturation point

Condenser Coil (or Outdoor Coil)

A series or network of tubes filled with refrigerant, normally located outside the house, which remove heat from the hot, gaseous refrigerant so that the refrigerant becomes liquid again

Condenser Fan

The fan that distributes air over the air-cooled condenser

Contactor

A switch that can repeatedly cycle, making and breaking an electrical circuit; when ample current flows through the A-coil which is built into the contactor, the resulting magnetic field causes the contacts to be pulled in or closed

Crankcase Heater

This is the electric resistance heater installed on compressor crankcases to keep the crankcase oil at a temperature higher than the coldest part of the system to prevent migration. Many newer cooling systems do not require crankcase heaters, however, heat pumps do require crankcase heaters. Crankcase heaters are used to overcome the problem of migration and condensation of refrigerant in the crankcases of compressors used in air conditioning and heat pump systems.

Damper

Found in ductwork, this movable plate opens and closes to control airflow. Dampers can be used to balance airflow in a duct system. They are also used in zoning to regulate airflow to certain rooms.

Defrost

The process of removing ice or frost buildup from the outdoor coil during the heating season

Degreeday

A computation that measures the amount of heating or cooling needed for a building; a degreeday is equal to 65 degrees Fahrenheit minus the mean outdoor temperature

Dehumidifier

An air cooler that removes moisture from the air; this unit reduces water vapor in air by cooling the air below the dew point, removing water vapor from the air by chemical means, refrigeration, etc.

Diffuser

A grille over an air supply duct having vanes to distribute the discharging air in a defined pattern or direction

Downflow Furnace

A furnace that pulls in return air from the top and discharges warm air at the bottom

Drain Pan

Also referred to as a condensate pan; this is a pan used to catch and collect condensate (in residential systems vapor is liquefied on the indoor coil, collected in the drain pan, and removed through a drain line)

Dry Bulb Temperature

Heat intensity, measured by a dry bulb thermometer

Ductwork

A pipe or conduit through which air is supplied; ducts are typically made of metal, fiberboard, or a flexible material. In a home comfort system, the size and application of ductwork is critical to performance and is as principal as the equipment.

DX

Direct expansion; a system in which heat is passed on by the direct expansion of refrigerant

EER

Energy Efficiency Ratio (steady state); means the ratio of the cooling capacity of the air conditioner in British Thermal Units per hour to the total electrical input in watts under ARI-specified test conditions

ENERGY STAR®

Trane high-efficiency systems carry the ENERGY STAR® label, which is the result of Trane’s partnership with the U.S. Department of Energy and Environmental Protection Agency (EPA). ENERGY STAR® products are more energy efficient and help reduce our whole earth’s pollution issues. Choosing a Trane ENERGY STAR® Comfort System assures homeowners of lower energy bills and improved indoor air quality for their home.

EPA

Environmental Protection Agency; ENERGY STAR® is a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy helping us all save money and protect the environment through energy efficient products and practices

Evaporator Coil (or Indoor Coil)

The other half of an air conditioning system, this network of tubes filled with refrigerant, which is located inside the home within the indoor unit, taking heat and moisture out of indoor air as liquid refrigerant evaporates

Expansion Valve

A refrigerant-metering valve with a pressure or temperature controlled orifice

Fahrenheit

The temperature scale on which water freezes at 32 degrees and boils at 212 degrees, designated by the letter F; to convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit number, multiply by 5, and divide by 9 (77 32 equals 45, times 5 equals 225, divided by 9 equals 25 degrees Celsius). This is the most commonly used scale of temperature measurement in the United States of America.

Fan

Any device that creates air currents

Filter

Any device used to remove dust and other impurities from air for the purposes of reducing the load on the respiratory system and to protect the HVAC equipment through a straining process; filters vary greatly in particle arrestant—the higher the MERV rating (Minimum Efficiency Reporting Value, a number from 1 to 16 that is relative to an air filter’s efficiency), the better the filter

Flue

Any vent, duct, pipe, or chimney for carrying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors

Furnace

That part of an environmental system which converts gas, oil, electricity, or other fuel into heat for distribution within a structure

Fuse

A fuse is a type of overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows, which breaks the circuit in which it is connected, thus protecting the circuit’s other components from damage due to excessive current.

Gas Furnace Heat Exchanger

Found in the furnace, the heat exchanger transfers heat to the surrounding air, which is then transported throughout your home.

Heat Exchanger

An area, box, or coil where heat flows from the warmer to the colder fluid or surface

Heat Gain

The amount of heat introduced to a space from all heat producing sources by appliances, solar energy, occupant respiration, and lighting

Heat Loss

The rate of heat transfer from a building interior to the outdoors

Heat Pump

An automated compression cycle refrigeration system that can be switched to either heat or cool the controlled space

Heat Transfer

The movement of heat energy from one area to another; the means for such movement are convection, conduction, and radiation. Heat will flow naturally from a warmer to a cooler space or material.

Heating Coil

Any coil that serves as a heat source

Hertz

A measure of the number of cycles or wavelengths of electrical energy per second; U.S. electricity supply has a standard frequency of 60 hertz

HSPF

Heating Seasonal Performance Factor; this rating is used in measuring the heating efficiency of a heat pump by taking in account the variations in temperature that can occur within a season and is the average number of BTU of heat dispatched for every watt-hour of electricity used by the heat pump over a heating season. The higher the number, the more efficient the heat pump system.

Humidifier

A machine that adds water vapor to the air to increase humidity

Humidistat

A humidity sensing device designed to regulate humidity input by reacting to changes in the moisture content of the air

Humidity

The measure of the moisture content of air; air conditioners can remove moisture for added comfort

Humidity, Absolute

The ratio of the mass of water vapor to the volume occupied by a mixture of water vapor and dry air; it is measured in grams of water vapor per cubic meter of air

Humidity, Relative

A measure of the percent of moisture actually in the air compared with what would be in it if it were fully saturated at that temperature; when the air is fully saturated, its relative humidity is 100 percent

HVAC

Heating, ventilating, and air conditioning

Ignition

The lighting of a gaseous mixture to the temperature at which combustion takes place

Kilowatt (kW)

1,000 watts; a common unit of electrical consumption measured by the total energy created by one kilowatt in one hour

Latent Heat

A type of heat, which when added to or taken from a substance, does not change the temperature of the substance yet enables the heat energy to change its state

Media

The material in a filter that traps and holds the impurities; these HVAC filter media include fiberglass filter media, polyester filter media, dog hair filter media, blue/green filter media, charcoal filter media, and others

OEM

Original equipment manufacturer

Package Unit

A heating and cooling system contained in one outdoor cabinet; this package unit is typically installed on the roof, outside, or sometimes in the attic of a home

PSI

Pounds per square inch

PSIA

Pounds per square inch, absolute

PSIG

Pounds per square inch gauge

PVC

Polyvinyl chloride, a type of plastic; in recent years, PVC has been replacing traditional building materials such as wood, concrete, and clay in many areas

Reciprocating Compressor

A compressor that uses pistons driven by a crankshaft to deliver gases at high pressure

Refrigerant

A chemical substance that produces a refrigerating effect while expanding and vaporizing

Refrigerant Charge

The required amount of refrigerant in a system

SEER

Seasonal Energy Efficiency Ratio—a measure of seasonal or annual efficiency of a central air conditioner or air conditioning heat pump; it takes into account the variations in temperature that can occur within a season and is the average number of BTU (British thermal units) of cooling delivered for every watt-hour of electricity used by the heat pump over a cooling season. The higher the SEER, the more efficient the unit. The more efficient the unit, the lower the operating cost. The U.S. Government’s minimum SEER rating is 13.

Self-Contained System

A refrigerating system that can be moved without disconnecting any refrigerant lines; also known as a package unit

Sensible Heat

That heat which, when added to or taken away from a substance, causes a change in temperature

Sensor

Any device that responds to a change in the conditions being measured, permitting the condition to be controlled

Setpoint

The temperature or pressure at which a controller is set for desired comfort level

Spine Fin™ Coil

All aluminum outdoor coil that features the patented Spine Fin™ design; Spine Fin™ consists of thousands of tiny spines bonded to continuous aluminum refrigerant tubing. The tiny spines create a greater surface area, helping it to transfer more heat from your home more efficiently. It provides greater heat exchanging capabilities (meaning higher efficiencies) and is more resistant to corrosion than traditional copper/aluminum.

Split System

The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler); split systems must be paired for optimal efficiency. This is the most common type of system installed in a home.

Thermostat

A series of sensors and relays that monitor and control the functions of a heating and cooling system by turning the device on or off when a specified temperature is reached

Thermostatic Expansion Valve

A thermostatic expansion valve (TXV) is precision device used to meter the flow of liquid refrigerant entering the evaporator at a rate that matches the amount of refrigerant being boiled off in the evaporator; also called a thermal expansion valve.

Ton

A unit of measurement used for determining the cooling capacity of a system—one ton of cooling is based on the amount of heat needed to melt one ton (2000 lbs.) of ice in a 24-hour period. One ton of cooling is equal to 12,000 BTU/hr.

Two-Stage Cooling

The air conditioner/heat pump has a compressor with two degrees of operation: high for hot summer days and low for cooler days. While the low setting is adequate to meet household-cooling demands 80% of the time, a two-stage unit runs for longer periods and produces more balanced temperatures.

Two-Stage Heating

The furnace has two stages of heat output: high for cold winter days and low for milder days. Since the low setting is adequate to meet household-cooling demands 80% of the time, a two-stage unit runs for extended periods and delivers more uniform heat distribution.

U-Factor

The factor amounting to the resistance of heat flow through various building materials

UL

Underwriters Laboratories

Upflow Furnace

A furnace in which air is drawn in through the bottom or sides and expels warm air out the top

Vacuum

A pressure below atmospheric pressure; 30 inches mercury (periodic symbol "Hg") is a perfect vacuum

Variable Speed Motor(s)

The fan motor inside Trane’s variable speed air handlers is designed to vary its speed based on your home’s heating and air conditioning requirements. Working in conjunction with the thermostat, it keeps the appropriate temperature air (e.g. warm air on cold days) circulating throughout your home, reducing temperature variances in your home. It also provides greater air circulation and filtration, better temperature distribution, humidity control, higher efficiency, and quiet performance.

Volt

A unit of measure of electrical force given to the electrons in an electric circuit—a single volt is the electromotive force that will cause a steady current of one ampere to surge through a resistance of one ohm; abbreviated by the symbol "v"

Voltage

The force that pushes electrical current along wires and cables; the term voltage used to indicate the potential difference in a circuit and is also known as the pressure which causes current to flow

Watt

The unit of electrical power equal to the flow of one amp at a potential difference of one volt; a single watt is equivalent to the work done at a rate of 1 joule (the SI unit of energy measuring heat, electricity and mechanical work) per second

Wet Bulb Thermometer

A thermometer whose bulb is covered with a piece of water-soaked cloth; it is a type of temperature measurement that reflects the physical properties of a system with a mixture of a gas and a vapor, usually air and water vapor

Zoning System

A method of sectioning a home into different comfort zones so each zone can be individually controlled depending on use and need; an air conditioning system capable of maintaining diverse conditions for various rooms or zones