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Heating & Air Conditioning Glossary


Annual Fuel Utilization Energy measures the efficiency of a furnace or boiler. It is the ratio of heat output compared to the energy in the fossil fuel used. An AFUE of 95 percent means 95 percent of the energy in the fuel becomes heat; the other 5 percent leaks out through the chimney or elsewhere.

Advanced Reciprocating Compressor

A compressor that uses pistons to compress the refrigerant. It is a more effective method for condensing refrigerant and results in better cooling efficiency.

Air Handler

A mechanical device in an air conditioning system that heats or cools the air and distributes it through a home or a building.


British Thermal Unit is the amount of heat necessary to raise the temperature of 1 pound of water by 1 degree Fahrenheit. In heating, BTU measures the amount of heat created when fuel is burned. In cooling, BTU measures the amount of heat removed from a home or building.


British Thermal Units per Hour is the accurate term to use when discussing heating and cooling systems; however, it is often abbreviated to BTU.

Beckett Burner

A burner assembly inside an oil or gas furnace that is manufactured by Beckett in accordance to precise requirements set by Carrier.


Cubic Feet per Minute is a measure of airflow that specifies how many cubic feet of air pass by a stationary position in one minute. The higher the CFM, the more air is being forced through the system.


The capability of a heating or air conditioning system to heat or cool a specified amount of space. This capacity is stated in BTUs. For cooling, it can also be stated in watts or tons of refrigeration.

Carbon Monoxide

A tasteless, colorless and odorless gas that is highly toxic to humans. It is created when fuels such as natural gas or coal burn without a source of oxygen.

Comfort Heat Technology

Carrier’s exclusive technology that calculates the need for heat based on previous furnace cycles. It evens out heat cycles and reduces temperature swings.

Comfort Heat Technology Pump System

Carrier’s trademark heat pump system that delivers a warm supply of air through the registers for greater occupant comfort.


The compressor is the part of a heat pump or air conditioner unit that puts the refrigerant gas under pressure and turns it back into a liquid; this pressure creates heat. In the winter, the heat is used to warm a home; in the summer, the heat is removed from the home to keep it cool.

Condenser Coil

The condenser coil is the part of an air conditioner or heat pump that carries the heat generated by the compressor to the outside.


Decibels (dB) measure the intensity of sound.


A valve in ductwork that controls airflow. Valves can be opened or closed to regulate the amount of cool or warm air distributed to individual rooms or areas, also referred to as zones, in a home or building.


A type of furnace where the cool air comes in at the top, is heated and then is released out the bottom of the furnace. Often used in homes with a crawl space or that are built on a slab.


Empty pipes that carry the heated or cooled air from the air handler and distribute it throughout the home or building. Most often made of galvanized sheet metal. Ductwork also carries ventilation air.


The Energy Efficiency Rating (EER) measures the efficiency of an air conditioner. It is the ratio of cooling output compared to the energy in the fuel used. The higher the EER, the more efficient the unit is. More often expressed as SEER (seasonal energy efficiency rating.)


ENERGY STAR® is a federal strategy designed to protect the environment by promoting products that use less energy. Products with the ENERGY STAR rating are efficient and save money on utility bills.

Electronic Air Cleaner (EAC)

An electronic appliance that filters and removes impurities from indoor air.

Energy Saver Switch

A switch that triggers the compressor in an air conditioner to cycle off when the heat exchanger has reached its maximum capacity; the fan continues to run, using up the stored cooling energy. When the stored cooling energy is used up, the compressor is switched back on and resumes running. This prevents inefficient overcooling and saves on energy.

Evaporator Coil

The evaporator coil is the part of an air conditioning unit or heat pump that converts liquid refrigerant into a gas. The coil becomes either warm or cold when the system operates. Air moving across the coil is warmed or cooled and then distributed throughout the building.

Fan Coil

The part of an air conditioner unit or heat pump system that changes the refrigerant from a gas to a liquid. The fan coil unit is comprised of a coil and a fan; it is used in place of a furnace and evaporator coil.


The Heating Seasonal Performance Factor indicates the heating effectiveness of an air source heat pump. It is a ratio of BTU heat production compared to the watt-hours of electricity used. The higher the HSPF, the more efficiently the heat pump heats a building.


Stands for Heating, Ventilation and Air Conditioning. HVAC relates to the technology of indoor comfort.

Heat Exchanger

A device that transfers heat from one medium to another. In a furnace, it is the part that conveys heat to the air; in an air conditioner, it is the condenser or evaporator coil.

Heat Pump

A device that takes heat from one area and moves it to another area. In the summer, a heat pump removes heat from indoor air and moves it outdoors. In cold weather, heat is removed from the outside air and moved indoors.

Horizontal Flow

A type of furnace where the cool air comes in on one side, is heated and then is released out the other side of the furnace. Often used in cramped spaces such as attics or crawl spaces.


An appliance that adds moisture to a room by adding water vapor to the air. Humidifiers can be individual, point-of-use or whole-house.

Hybrid Heat

Hybrid heat is a system that pairs a furnace with a heat pump rather than with an air conditioner.


Carrier’s innovative defrost management technology for maintaining the best defrost interval for a heat pump, thus improving efficiency and comfort.


Carrier’s trademark innovative humidity management technology for maintaining ultimate comfort in a home.

Indoor Coil

The same as an evaporator coil. In a split system, the evaporator coil is located inside the home.


The part of an air conditioner that controls the speed of the compressor to equal the heating and cooling load. It evens out temperature fluctuations and reduces stop-start cycles.

Load Estimate

The number of BTUs per hour needed to keep a building at a specific temperature. The load calculation determines the size of the heating and cooling system needed for a specific space. Factors considered include square footage, number of doors and windows, number of occupants, amount and quality of insulation and climate.

Low Boy

A type of furnace design where the fan, or blower, is located behind the heat exchanger rather than on top or underneath. A low boy is shorter and wider than a down flow, up flow or crossflow furnace.


The Minimum Efficiency Reporting Value measures the effectiveness of an air filter. The higher the MERV score, the better the filter is able to remove particles from the air.

Matched System

A heating and cooling system consisting of equipment that has been certified to perform at specific comfort and efficiency levels when used together in accordance with engineering and design specifications.

Operating Cost

The daily cost of running a home comfort system based on energy use.

Outdoor Coil

The same as the condenser coil. In a split system, the condenser coil is located outside the building.

Payback Analysis

A measure of the efficiency and value of your HVAC system. It determines the number of months needed before energy savings offset the purchase price.

Puron Refrigerant

Puron® refrigerant is a refrigerant that does not harm the environment. The EPA has approved it as a replacement for Freon 22.


QuieTech™ is a noise reduction method that supplies comfortable heat while creating very little noise.

R-22 refrigerant

A refrigerant used for more than 40 years in air conditioners. Often referred to as Freon, it is harmful to the ozone and the U.S. Environmental Protection Agency is phasing out its use.

Reciprocating Compressor

A compressor that uses pistons moving up and down to compress the refrigerant.


Sending back used refrigerant to the manufacturer for disposal or recycling.


Cleaning and reclaiming used refrigerant.

Refrigerant Lines

Lines that connect the outdoor condenser coil and the indoor evaporator coil. Usually made of copper.

Riello Burner

A burner assembly in an oil furnace manufactured by Riello to fit precise requirements from Carrier. It burns heating oil cleaner and more efficiently compared to other types of burners.


The Seasonal Energy Efficiency Ratio measures the cooling efficiency of an air conditioner or heat pump over an entire cooling season. The higher the number, the more effective the system is at changing electricity into cooling power.

Scroll Compressor

A compressor that uses a circular motion to compress the refrigerant.


Carrier’s proprietary Serpentuff™ Heat Exchanger uses a patented polypropylene laminate which extracts almost all of the heat from the system.

Setback Thermostat

An electronic thermostat that can be programmed to change automatically the temperature settings at different times during the day.

Silencer System

The Carrier Silencer System II guarantees quiet operation indoors and out. The forward sweep of the fan blades reduces noise while ensuring proper air velocity. A sound blanket wrapped around the compressor, motor mounts that reduce vibration and air baffles that absorb sound are other ways that Carrier systems meet or exceed community and trade sound criterion.

Single Package Product

A single package product is a heating or air conditioning system that is contained in one unit. The unit is located outdoors.


Carrier’s feature that automatically turns on the system in time for each zone to reach the required temperature at the scheduled time.

Split System

An air conditioning system or heat pump that has one part of the system, the evaporator coil, located inside the structure and the other part of the system, the condenser coil, located outside.


The Thermidistat™ Control monitors indoor humidity levels and indoor and outdoor temperatures; it automatically adjusts the system to maintain the humidity and temperature levels set by the homeowner.


A device that controls and monitors components of a heating and cooling system.

Thermostatic Expansion Valve

A device that controls the quantity of refrigerant that enters the evaporator.


One method of measuring the cooling capacity of an air conditioner. One ton of refrigeration is the degree of cooling produced by thawing one ton of ice at 32 degrees Fahrenheit in 24 hours. One ton equals 12,000 BTUH.

Total Home Comfort System

The best solution that delivers consistent, personalized comfort, regardless of the weather.

TrueSense Dirty Filter Detection

Carrier’s technology to remind homeowners when it is time to change the media filter.

Two Stage Compressor

A compressor that runs on two levels, low and high. A correctly sized HVAC system will run 80 percent of the time on low.


Underwriters Laboratory is an independent organization that examines, tests and rates electrical products for consumer safety.


A type of furnace where the cool air comes in at the bottom, is heated and then is released through a vent at the top. Often installed in a basement.


A device that brings fresh air into a home or building. It will also condition the incoming air to match the indoor air temperature.


Carrier’s innovative technology that protects outdoor units from the elements.


A special coating on the outdoor condenser coil that resists rust from salt air.


Zoning is a way to provide independent heating and cooling to different rooms or areas. Typically controlled by programmable thermostats for each area or by opening or closing dampers in each zone.