Glossary of Heating & Cooling Terms

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We’ve compiled this list of energy saving ideas to make your home and business more energy efficient and comfortable. Most of these ideas are easy to do and take only a few minutes to perform. By reducing energy usage in your area, we can help you keep your energy costs down as well as benefit the environment.


Acid Aerosol

Acidic liquid or solid particles that, in higher quantities, can be irritating and have been associated with some respiratory diseases, such as asthma.

Air Conditioner

Electronic device used for controlling the temperature and humidity of an indoor space.

Air Conditioning

The process of controlling temperature and humidity in an indoor environment.

Air Handler

In a forced air system, the device that functions to move air across the heat exchanger. Usually refers to the fan and housing.

Air Sensor

A device used to capture and record changes in air temperature, pressure, humidity, and velocity.

Air Vent

Openings in a system designed to allow for manual or automatic venting of air.


Any substance that triggers an allergic reaction within a person.

Animal Dander

Tiny particulates of animal skin.

Annual Fuel Utilization Efficiency

(AFUE)A measure of your furnace’s heating efficiency. The higher the AFUE percentage, the more efficient the furnace. The minimum percentage established by the DOE for furnaces is 78.00%.

Application Balance Point

The outdoor temperature at which the heat pump will need assistance from the back up heat to maintain indoor temperatures and is normally close to 30¼ outdoor temperature in the average Midwest home.

Automatic Control

Indoor comfort controls that react to changes in temperature and allow them to stabilize without user input.

Automatic Expansion Valve

A control valve that helps to maintain an even pressure in an evaporator.



A logarithmic unit used to measure sound ratings for machinery, including heating and cooling equipment. Lower is quieter. Every unit is ten-fold and a 0.1 difference is significant drop in the sound level of a unit.


Microscopic living organisms suspended in the air that grow and multiply in warm, humid places.


The process of moving slowly from one pressure level to another.

British Thermal Unit

(BTU)The standard measurement of how much heat is required to raise the temperature of a pound of water 1 degree Fahrenheit.


British Thermal Units Per Hour

Building-Related Illness

A disease that is caused by specific air pollutants or allergens within a building.


The device that directly burns fuel for heating purposes.



The Combined Annual Efficiency is a measure of the amount of heat produced for every dollar of fuel consumed for both home and water heating.

Carbon Dioxide

A byproduct of natural gas combustion, which is not harmful to humans or the environment.

Carbon Monoxide

A byproduct of an incomplete combustion process, this odorless, tasteless, colorless gas can be harmful to the human body.

Central Air Conditioning System

System in which air is treated at a central location; distributed to and from rooms by one or more fans and a series of ducts.


The amount of refrigerant in a cooling system.

Charging Cylinder

A device used by service technicians to recharge a refrigerant system with an accurate amount of coolant.
Chemical Sensitization
The development of health problems such as dizziness, eye and throat irritation, nasal congestion, and chest tightness upon being exposed to a chemical.


(CFC)A family of cooling refrigerants believed harmful to the ozone layer.

Circuit Breaker

A device that controls electrical currents by opening an electrical circuit when an overload occurs.

Co2 Indicator

An instrument utilized by technicians to aid in detecting the quantity of carbon dioxide in a flue.


Safety rules for installation and service of systems and equipment, established to protect the health of both customers and professionals.


Rapid oxidation that results in burning, often accompanied by light and heat.


A pump that increases vapor (refrigerant or air) pressure from one level to a higher level of pressure.


The collection of moisture that has condensed because of cold temperatures; in heating and air conditioning this commonly occurs on the evaporator coil.

Condensate Pump

A device used to pump the condensate that accumulates on a system to a higher level.


A device used to condense refrigerant in a cooling system.

Condensing Temperature

The proper temperature a vapor most be cooled to in order to convert it to a liquid.

Condensing Unit

The combination of a compressor and condensing coil.


The Coefficient Of Performance of a heat pump in the heating mode is the ratio for the rate of heat delivered compared to the rate of energy input at a specific outdoor temperature (rated by manufacturers at 17¼and 47¼). Higher ratings are better and there is no limit. See HSPF

Cost Per One Million BTU’s

Considered the best way to compare the heating costs associated with different fuels and different heating systems.


The full process of a heating or cooling system running from start to finish.



The portion of an airflow system designed to restrict flow for the purpose of proper temperature control and balance.


The process by which a system removes excess moisture from an environment.


The weight per unit of volume of a substance.

Department Of Energy

(DOE)A U.S. government agency tasked with creating and enforcing legislation designed to conserve energy.

Dew Point

The point of temperature at which condensation will begin to form.


Department of Energy


A component for refrigerant devices that removes excess moisture.

Drip Pan

A pan specifically designed to capture the condensation that drips from an evaporator coil.

Dual Fuel Heating

Uses a combination of affordable electric heat pump and a natural gas furnace to operate the system as higher efficiency while maintaining overall temperatures in the home.


The series of enclosed channels that carry air from heating and cooling systems throughout a controlled environment.


Economic Balance Point

The outdoor temperature at which the electric usage equals the utility cost of the selected furnace that the heat pump is matched with. Heat pumps have become significantly more efficient over the last 20 years and today’s heat pumps are more efficient than electric furnaces even when outdoor temperatures are below zero Fahrenheit.


Measured in watt hours. Electricity is usually sold to residential customers in units of 1000 watt hours or kilowatt hours (kWh)

Electronic Air Filter

A device used to aid in the collection of dust particles by changing their electronic and then collecting them on an oppositely charged plate.

Energy Efficiency Ratio

(EER)A standard efficiency rating calculated by dividing BTU output by the amount of watts required for operation, this figure does not include the start up and shut down of the system.

Energy Star

Joint program between the U.S. Environmental Protection Agency and Department of Energy to promote environmental preservation and energy conservation.

Environmental Protection Agency

(EPA)A U.S. government agency designed to help preserve the environment by enacting regulations and policies.

Environmental Tobacco Smoke

More commonly known as secondhand smoke, any smoke byproducts from lit tobacco and exhaled fumes.

Essential Financing

Financing plans designed to fit purchasing new systems and/or air quality products into any budget.

Essential Plumbing

Service plan designed to maintain home plumbing systems.

Essential Protection

Extended service warranty for heating and cooling systems.

Essential Service

Service contract designed to maintain heating and cooling systems.

Estimated Heating Costs

The difference of your total energy bill minus what it costs to run your other appliances. Your heating portion is probably the largest portion of your total energy bill.

Ethane Gas

A natural gas that is used for heating purposes.


The process by which a liquid is transferred into a vapor.

Evaporator Coil

The part of the air conditioner or heat pump that is located inside the air handler or attached to the furnace. Its primary function is to absorb the heat from the air in your house.


Fahrenheit Scale

Standard temperature scale that sets waterÕs freezing point 32 degrees and its boiling point at 212 degrees.


A device commonly used to displace air and move it throughout a designated area.

Fan Cycling

A system that utilizes a pressure control to turn a systems fan on and off, preserving a balance of pressure in the system.

Fan Relay Coil

The magnetic strip that starts and stops a fan.


A porous material used to separate particles and help purify liquids.


A duct system that is used to carry by-products of a fuel combustion system out of a home.

Freeze Up

A potentially harmful effect of excess frost accumulation on the evaporator coil; can be the cause of airflow issues.


An E.I. DuPont de Nemours & Co. manufactured refrigerant.


a group of parasitic plants that lack chlorophyll includes molds and mildew.


A heating system consisting of a blower fan, heat exchanger, and some method of controlling heat output, often runs on either gas, oil, or electricity.



A substance in a state of vapor with the ability to indefinitely expand and take any shape.

Gas Valve

A device used to regulate the flow of natural gas in a system.


A standardized unit used to detect the amount of pressure within a system.


system A heating/cooling system that uses the Earth’s natural warming/cooling properties in conjunction with a water-to-air heat pump.



(hydro chlorofluorocarbon) A fluorocarbon that is considered to be destructive to the ozone.

HCFC Phase Out

R-22 (a common refrigerant used in home cooling systems) is one of the HCFCÕs being phased out by the Montreal Protocol and will not be allowed to be put in any new air conditioning systems effective 2010.


An energy process through which molecules cause a rise in temperature, evaporation, or expansion in a substance.

Heat Anticipator

A device that preempts the need for a system to shut down in order to allow for cooling.

Heat Coil

Tube or piping carrying fluids designed to transfer heat between substances.

Heat Exchanger

A device that literally passes heat from one object to another.

Heat Pump

A device that utilizes compressible refrigerant to provide cooling or heating to a controlled environment.

Heating Seasonal Performance Factor

(HSPF)The Heating Seasonal Performance Factor is the heating efficiency rating for heat pumps. The higher the rating, the more efficient the heat pump. Effective 2006 the minimum HSPF for heat pumps manufactured in the US is 7.7.

HEPA Filtration

(High Efficiency Particulate Arresting Filtrations) A free standing devise that can be attached to a central heating/cooling system and provides one of the highest levels of air filtration available today.

High-Efficiency Heating System

A heating system that uses greater than 80% of the fuel to heat your home. Newer systems can reach up to 95% or greater efficiency.

Horizontal Flow

When an air handler or furnace is positioned on its side and circulates air in one end and out the other. Ideal for attic or crawl space installations.


A device used to control the amount of water vapor in an environment.

Humidifier Fever

An illness developed from an increase in microorganisms in an overly wet, humid environment.

Hybrid Heat

The electric heat pump serves as the primary heating source. When outdoor temperatures drop below 30°, your gas furnace takes over. This results in lower heating bills from the increased usage of electricity over expensive natural gas.

Hydro Chlorofluorocarbons

(HCFC)Cooling refrigerants that are believed to harm the environment through the depletion of the ozone layer.


Icm Motor

A variable speed motor that is capable of controlling the air flow in a system.

Ignition Transformer

Device that creates a spark to begin combustion in a fuel, oil, or gas furnace.

Indoor Air Quality

(IAQ)A measurement of the health and comfort of the air you breathe while inside your home, office or any other facility.

Induced Draft Motor

A fan-developed draft in the heat exchanger of a gas-fired furnace.

Inert Gas

Gases that are not capable of supporting certain chemical reactions.

Intermittent Ignition

A system of ignition in which a spark is created only when needed to begin combustion.

ISO 9000

A family of international standards for quality management and assurance


Junction Box

Box containing a series of electrical connections.



A kilowatt of electricity or 1,000 watts. Electric furnace capacity is sized in KW and 1 KW = 3,413 Btu


Limit Control

Controls that allow a user to halt system operation when a specified temperature or pressure is reached.

Line Set

Copper tubing used to carry refrigerant connecting the indoor unit to the outdoor unit of a cooling or heat pump system.


A substance with the ability to expand and take the shape of its container.

Liquid Line

Industry term referring to tubing that extends from the condenser to an expansion device.

Liquid Receiver

A device used to hold refrigerant in a refrigerant system.



The upkeep of an indoor comfort system to ensure cost-efficiency and prevent system failure.

MERV Rating

The MERV (Minimum Efficiency Reporting Value) efficiency rating of an indoor air filter. The higher the MERV rating the more efficient the filter is at removing air born particles.


A unit of measure equal to one millionth of a meter, used to describe the size of particles found in indoor air.

Montreal Protocol

An agreement for the reduction and eventual halt of production on refrigerant products responsible for ozone layer depletion.

Montreal Protocol

A Treaty, signed in 1987, governs stratospheric ozone protection and research, and the production and use of ozone-depleting substances. It provides for the end of production of ozone-depleting substances such as CFCS. Under the Protocol, various research groups continue to assess the ozone layer. The Multilateral Fund provides resources to developing nations to promote the transition to ozone-safe technologies.


Natural Gas

Fossil fuel formed by the degradation of vegetation and animal remains under the earthÕs surface.


A base substance used to counteract an acid.


A high pressure inert gas used to test for leaks in a refrigerant system.



Air contaminants in the form of gases.

Organic Compounds

Found in many household products, these compounds vaporize at room temperature and pressure and can be harmful to humans and animals.

Outdoor Coil

See Condenser Coil


Oxygen mixing with another material to form a new substance. This results in the degradation of the material. An example would be the rusting of metals.


A layer of the stratosphere that helps to prevent an overabundance of ultraviolet rays from reaching the earthÕs surface.


Package Unit

A heating and/or cooling system in which all of the components are consolidated into a single housing that can be placed on the roof or on the ground.


Any substances measuring less than 100 microns in diameter. The EPA has found that small particles (less than 2.5 microns) are responsible for the health effects of greatest concern.

Pico Curie

(pCi)A unit for measuring radioactive activity.

Pilot Light

The flame responsible for initiating the combustion process in a gas furnace.


A sealed chamber attached to the air handler, through which air is transferred into the ductwork of a system.

Polyvinyl Chloride

(PVC)Plastic piping often used to transport liquids and gases.

Pounds Per Square Inch

(PSI)Stands for Pound Per Square Inch.

Pressed Wood Products

Materials used for building and construction purposes, containing wood particles bonded together under heat and pressure.


The exertion of force upon a surface by an object, fluid, or other substance.

Pressure Limiter

A device designed to open when a set pressure is achieved.

Pressure Switch

A switch designed to operate with the changes of pressure in a system.

Programmable Thermostat

A thermostat with the ability to be set at different temperature settings at different time settings for heating and/or cooling equipment.


A colorless, flammable gas often used for heating.


The act of fully removing a liquid from a system.



An air conditioning refrigerant that is being phased out by the federally mandated Montreal Protocol and will no longer be allowed to be placed in new air conditioners effective 2010.

R410 Refrigerant

A liquid that vaporizes at a low temperature utilized in cooling systems (see R-22 and R-410a).


A liquid that vaporizes at a low temperature utilized in cooling systems.

Refrigerant Recovery

The removal of refrigerant from a system into an external storage container for recycling as required by EPA Section 608 regulations.

Refrigerant Recycling

A procedure through which refrigerant is purified, often by passing through filter-driers or other filtering devices.


The act of moving hot air out of a controlled environment and into another environment where temperature is of no importance.


A device through which electromagnetic charges are used to operate other devices such as switches and valves.

Relief Valve

A valve designed to open after a specific pressure is reached in a system.

Rollout Switch

A safety device utilized to open circuits if a flame escapes the burner box.


A rotating or moving component of a system motor.


Scroll Compressor

Scroll technology use advances engineering and flow dynamics to efficiently and smoothly compress gas refrigerant. Older technology reciprocating compressors use pistons and valves to compress and move gas.

Seasonal Energy Efficiency Ratio

(SEER)A cooling system efficiency rating of an air conditioner or heat pump in the cooling mode. A ratio of total cooling in comparison to the electrical energy input in watts per hour. Higher ratings are better and there is no limit. The DOE’s established minimum SEER rating for cooling is 13.00.


A device that is capable of changing its form or shape when conditions require.

Service Valve

A refrigeration system valve that can be utilized in various service procedures to prevent the need to recover refrigerant during a repair.

Short Cycle

Short cycling results from oversized equipment.

Split System

An air-conditioning system in which the condensing unit and evaporator coil are not within close vicinity of each other. The most typical and traditional heating and cooling systems are split systems with the furnace or air handler in the home and the condenser (air conditioner or heat pump) outside the home.

Sub Cooling

The temperature of a liquid after it has been cooled below the point where it condenses.



The heat of molecular activity.


A safety device used in older gas furnaces with a standing pilot that prevents gas from passing through if the pilot light goes out. Newer gas furnaces do not have thermocouples.


Used to measure temperature levels.


A device that helps to either maintains a consistent temperature or helps a system to reach a desired temperature. (See programmable thermostat)

Thermostatic Expansion Valve (TXV)

A refrigerant metering device used to adjust the flow of liquid refrigerant entering the evaporator coil to the most efficient rate that best matches indoor temperature and outdoor conditions. Some cooling systems have fixed metering devices that do not adjust as indoor/outdoor conditions change and as a result normally are not as efficient and are more prone to indoor coil freeze up during cool outdoor temperatures.

Ton Of Refrigeration

The amount of heat required to melt a ton (2000 lb) of ice at 32’F, 288,000 Btu in a 24 hour period or 12,000 Btu per hour. Air conditioners and heat pumps are sized based on tonnage. A two ton air conditioner as approximately 24,000 Btu of cooling capacity.


A device used to transfer electric energy from one circuit to another, usually consisting of coil or wire wrapped around an iron core.

Two-Stage Operation

Provides two levels of heating or cooling output for greater temperature control, energy efficiency and improved indoor air quality.



Rays of light that exceed the violet portion of the light spectrum.


When an air handler or furnace is installed in an upright position and circulates air through the side or bottom and out through the top. Typically used in basement, closet and attic installations.


Vacuum Pump

A pump capable of removing air and moisture from a system under pressure below the earthÕs atmosphere.


Used in a system to control fluid flow.


A substance in a gaseous state.

Vapor Lock

Gas trapped in a liquid line that stops the flow of liquid.

Vapor Pump

See Compressor.


The transformation of liquid into a gaseous state.

Variable Speed Moto

A motor that automatically adjusts the flow of warm or cool air for ultimate comfort.


The speed at which a substance passes a point.


A system that exchanges stale, re-circulated indoor air with fresh, filtered outside air.



An International System unit of power, where one watt equals 3.414 BTU.



A method of partitioning a home into independently controlled comfort zones for enhanced comfort and efficiency.

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