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Industry Terminology

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


Abbreviation for alternating current, an electric current that reverses its direction many times a second.

AC or DC

Abbreviation for equipment capable of operating on alternating or direct current.


Air Conditioning Contractors of America.


Of or pertaining to sound.


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. The unit is more efficient when the rating is higher.


Abbreviation for American Gas Association, Inc.

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 your air conditioner or heating system that forces air through your home's ductwork.


Air Conditioning & Refrigeration Institute.


American Society of Heating, Refrigeration and Air Conditioning Engineer.



British Thermal Unit. Used for both heating and cooling, BTU is a measure of the heat given off when fuel is combusted. Or for cooling, it's a measure of heat extracted from your home. (One BTU is approximately equal to the heat given off by a wooden kitchen match.)


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


A 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.



The ability of a heating or cooling system to heat or cool a given amount of space. For heating, this is usually expressed in BTU's. For cooling, it is usually given in tons.


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).


Stands for Cubic Feet per Minute. A measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being forced through the system.


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

Comfort Heat

Carrier's exclusive Comfort Heat technology accurately predicts the need for heating while cutting temperature swings in half.

Comfort Heat Pump System

Comfort Heat Pump System is Carrier's exclusive heat pump system that provides significantly warmer supply air from the registers for enhanced occupant comfort.


Part of a split-system heat pump or air conditioner's outdoor unit that controls the pressure applied to the refrigerant, necessary for taking in heat to warm your home with a heat pump or getting rid of heat to keep your home cool.


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.


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

Condenser coil (or outdoor coil)

Part of the outdoor portion of a split-system air conditioner or heat pump. By converting refrigerant that is in a gas form back to a liquid, the coil sends heat carried by the refrigerant to the outside.

Condenser Fan

The fan that distributes air over the aircooled condenser.


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.



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.


Direct current electricity. This type of electricity (as opposed to Alternating Current, or AC) flows in one direction only, without reversing polarity.


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


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.


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.


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


Department of Energy

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.

Dry Bulb Thermometer

An device that measures air temperature independently of humidity.


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.


Hollow pipes used to transfer air from the Air Handler to the air vents throughout your home. Ductwork is one of the most important components of a home heating and cooling system.


Direct expansion. A system in which heat is passed on by the direct expansion of refrigerant.



Energy Efficiency Ratings (EER) measure the efficiency with which a product uses energy to function. It is calculated by dividing a product's BTU output by its wattage.


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)

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 (or vice-versa). A blower motor, typically in a furnace, then moves air over the coil to either heat or cool your home.

Expansion Valve

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



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.


Any device that creates air currents.

Fan Coil

An indoor component of an air conditioner or heat pump system, used in place of a furnace and evaporator coil, to provide change the refrigerant from a gas to a liquid (or vice-versa) and blow air over the coil to cool or heat your home.


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.


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


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


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 Appliance Manufacturers Association.

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.
A device for the transfer of heat energy from the source to the conveying medium.

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

A product that works just like an air conditioner in cooling mode; however, in heating mode, the refrigerant flow is reversed and heat is extracted from the outside air to heat your home.

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.


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.


The 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.


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


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


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.


Heating, Ventilating and Air Conditioning.



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.



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.


The Minimum Efficiency Reporting Value is the standard comparison of the efficiency of an air filter. The MERV scale ranges from 1 (least efficient) to 16 (most efficient), and measures a filter's ability remove particles from 3 to 10 microns in size.



National Energy Council / National Electric Code.


National Energy Council / National Electric Code.


National Electrical Manufacturing Association.



Original equipment manufacturer.


Package Unit

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


Pounds per square inch.


Pounds per square inch, absolute.


Pounds per square inch gauge.

Puron Refrigerant

Puron® Refrigerant is an environmentally sound refrigerant designed not to harm the earth's ozone layer. Federal law requires that all manufacturers phase out ozone depleting refrigerants in the next few years. Puron Refrigerant is approved by the US Environmental Protection Agency as a replacement for Freon 22*.


R-22 Refrigerant

R-22 is a single component HCFC refrigerant with low ozone depletion potential. It has long been used in a variety of air-conditioning and refrigeration applications in a variety of markets. Production of R-22 will cease in 2015 per the Montreal Protocol.

Reciprocating Compressor

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


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

Refrigerant Charge

The required amount of refrigerant in a system.


Scroll Compressor

A specially designed compressor that works in a circular motion vs. an up and down piston action.


The Seasonal Energy Efficiency Ratio is a measure of the cooling efficiency of your air conditioner or heat pump. The higher the SEER number, the more efficient the system is at converting electricity into cooling power.

Self Contained System

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

Sensible Heat

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


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


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.

Split System

Refers to an air conditioner or heat pump that has components in two locations. Usually, one part of the system is located inside (evaporator coil) and the other is located outside your home (condenser coil).



The Thermidistat™ Control monitors temperatures both inside and outside, as well as indoor humidity and adjusts system operation to maintain the temperature and humidity levels set by the homeowner.


Unit that monitors and controls your HVAC system products.

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.


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 Compressor

Two Stage Compressors are capable of two levels of operation, a low stage and a high stage. Properly sized equipment will operate 80% of the time in low stage, enhancing efficiency and comfort with lower humidity levels and quieter operation. It's like getting two air conditioners or heat pumps in one system.

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.



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


Underwriters Laboratories.

Upflow Furnace

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



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


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".


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



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.

Weather Armor

Weather Armor™ is a Carrier innovation that protects outdoor units from weather and increases durability.

Wet Bulb Thermometer

A thermometer whose bulb is covered with a piece of watersoaked 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.


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Simpson Air is a BBB Accredited Air Conditioning Company in Tampa, FL

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