Annual Fuel Utilization Efficiency. Indicated as a percentage, your furnace's AFUE tells you how much energy is being converted to heat. For example, an AFUE of 90 means that 90% of the fuel is being used to warm your home, while the other 10% escapes as exhaust with the combustion gases.

Advanced Reciprocating Compressor

Type of compressor that uses a more efficient process for compressing refrigerant for better cooling efficiency.

Air Exchange Rate

In HVAC, the rate at which outside air replaces indoor air in a space. Expressed in one of two ways: the number of changes of outside air per unit of time - air exchanges per hour (ACH); or the rate at which a volume of outside air enters per unit of time - cubic feet per minute (CFM)

Air Handler

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



In HVAC, the device in an air conditioner that distributes the filtered air from the return duct over the coil/heat exchanger. This circulated air is cooled/heated and then sent through the supply duct, past dampers, and through supply diffusers to the living/working space.


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.)


A British Thermal Unit (BTU) is the unit of heat required to raise 1 pound of water by 1 degree Fahrenheit. BTUH is British Thermal Units per Hour.



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.


Coefficient of performance, an efficiency ratio that compares the amount of heat delivered to the amount of energy used. As with MPG on a car, the higher the score the more energy efficient the equipment is.


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


A device used to start a motor or compressor (or to keep it running after start up).

Carbon Monoxide

A colorless, odorless, highly poisonous gas produced when carbon-based fuels, such as natural gas, burns without sufficient air nearby.

Charging the Refrigerant

The procedure an HVAC technician performs to ensure that the system has enough of the right kind of refrigerant for peak operating performance.


The final step in installing a heating or air conditioning system. Every component is checked and tested for compliance with codes, manuals and manufacturer requirements.


Part of the heat pump or air conditioner unit that controls the pressure applied to the refrigerant, necessary for taking in heat to warm your home or getting rid of heat to keep your home cool.

Condenser 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. Also referred to as an Outdoor Coil.

Conditioned Space

The interior space of a building that is heated or cooled.


An electromagnetic actuated relay. Usually used to refer to the relay which closes the circuit to a compressor. In the condenser, the main switch that turns the condenser on.

Cooling Capacity

The quantity of heat that a cooling appliance is capable of removing from a room in one hour.



Decibels (dB) are a unit measuring the intensity of noise.


HVAC term for controls that vary airflow through an air outlet, inlet or duct. A damper position may be immovable, manually adjustable or part of an automated control system. Used in zoning to control the amount of warm or cool air entering certain areas of your home.

Defrost Cycle (Heat Pump)

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

Diffuser and Grilles

Components of the ventilation system that distribute and return air to promote air circulation in the occupied space. Supply air enters a space through a diffuser or vent and return air leaves through a grille.


A type of furnace that takes cool air from the top and blows warm air to the bottom-common where your furnace must be located in a second-floor closet or utility area.


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.



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.

Electronic Air Cleaner (EAC)

An electronic device that filters out large particles and contaminants in indoor air. It then electronically pulls out tiny particles that have been magnetized, such as viruses and bacteria, drawing them to a collector plate.

Energy Star

Energy Star is a government-backed program helping businesses and individuals protect the environment through superior energy efficiency. Products with the Energy Star rating will be efficient and save cost on energy bills.

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). Also referred to as an indoor coil.


Fan Coil

An indoor component of a heat pump system, used in place of a furnace, to provide additional heating on cold days when the heat pump does not provide adequate heating.

Filter (air)

A device that removes contaminants by mechanical filtration, from the fresh air stream before air enters the living space. Filters can be installed as part of a heating/cooling system through which air flows for the purpose of removing particulates before or after the air enters the mechanical components.

Filter Drier

A device that removes moisture, acid and foreign matter from the refrigerant.


The structure in a residential heating appliance into which combustion gases flow and are contained until they are emitted to the atmosphere.

Forced Air (system or furnace)

HVAC term for a type of heating system in which heated air is blown by a fan through air channels or ducts to rooms.


A registered trademark for a chlorofluorocarbon (CFC) gas that is highly stable and that has been historically used as a refrigerant.


In HVAC, a combustion heating appliance in which heat is captured from the burning of a fuel for distribution, comprised mainly of a combustion chamber and heat exchanger.



Hot surface ignitor - a small ignition device that allows the gas furnace to start up. These ignitors have all but replaced the older standing pilot light systems and are most commonly made from ceramic or silicon nitride.


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.


Term used for heating, ventilation, and air conditioning.

Heat Exchanger

The part of a furnace that transfers heat to nearby air. That air is then distributed through the ductwork throughout your home.

Heat Load

A series of studies performed to determine the heating or cooling requirements of your home. An energy load analysis uses information such as the square footage of your home, window or door areas, insulation quality and local climate to determine the heating and cooling capacity needed by your furnace, heat pump or air conditioner. When referring to heating, this is often known as a Heat Loss Analysis, since a home's heating requirements are determined by the amount of heat lost through the roof, entry ways and walls.

Heat Pump

A heating and air conditioning unit that heats or cools by moving heat.

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.


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.


A control used to manually maintain humidity at a fixed point.



Indoor Air Quality (IAQ) refers to the cleanliness and health of the air in a home.

Indoor Coil

see Evaporator Coil


Line Set

Two copper lines that connect the Condenser (Outdoor) Coil to the Evaporator (Indoor) Coil.

Load Estimate

A series of studies performed to determine the heating or cooling requirements of your home. An energy load analysis uses information such as the square footage of your home, window or door areas, insulation quality and local climate to determine the heating and cooling capacity needed by your furnace, heat pump or air conditioner. When referring to heating, this is often known as a Heat Loss Analysis, since a home's heating requirements are determined by the amount of heat lost through the roof, entry ways and walls.



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.

Matched System

A heating and cooling system comprised of products that have been certified to perform at promised comfort and efficiency levels when used together, and used according to design and engineering specifications.


A multi-direction configuration that allows for both up flow and down flow installations.


Operating Cost

The day-to-day cost of running your home comfort equipment, based on energy use.

Outdoor Coil

see Condenser Coil


Payback Analysis

Overall measure of the efficiency and value of your home comfort system. By combining your purchase price and ongoing operating costs, a payback analysis determines the number of years required before monthly energy savings offset the purchase price.


HVAC term for an air compartment connected to a duct or ducts.

Preventative Maintenance

A program of building maintenance implemented to reduce the possibility of problems, usually through periodic inspection, cleaning, adjustment, calibration, and replacement of functioning parts of the HVAC system, as well as housekeeping practices to reduce the buildup of potential contaminants. Primarily done on a building's mechanical systems, this involves a regular and systematic inspection, cleaning, and replacement of worn parts, materials, and systems. Preventative maintenance helps to prevent parts, material and system failure by ensuring that parts, materials and systems are in good working order.

Programmable Thermostat

A type of thermostat that allows the user to program into the device's memory a pre-set schedule of times when certain temperatures are to occur to operate HVAC equipment.

Pump down

Process of pumping refrigerant out of the evaporator and suction line at the end of the on- cycle by closing a solenoid valve in the liquid line and letting the compressor shut-off by the low pressure control.


R Value (insulation)

A measure of the capacity of a material to resist heat transfer. The R-value is the reciprocal of the conductivity of a material (U-value). The larger the R-Value of a material, the greater it's insulating properties.


The compound (working fluid) used in air conditioners and heat pumps to transfer into or out of an interior space. This fluid boils at a very low temperature enabling it to evaporate and absorb heat.

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

R-410A refrigerant

The replacement refrigerant to R-22. Does not contain chlorine and is safer for the environment.

Reciprocating Compressor

A type of compressor used in air conditioners that compresses refrigerant by using a type of "piston" action.


Returning used refrigerant to the manufacturer for disposal or reuse.


Removing, cleaning and reusing refrigerant.

Refrigerant Lines (Line set)

Two copper lines that connect the Condenser (outdoor) Coil to the Evaporator (indoor) Coil.


Combination grille and damper assembly covering an air opening or end of an air duct. Coverings for the ducts where they open to the conditioned space. (Same as Grilles.)


A device used to open and close an electrical circuit. The relay may may be actuated by a bimetal electrically heated strip, a rod wrapped with a fine resistance wire causing expansion when energized, a bellows actuated by expansion of a fluid or gas or an electromagnetic coil.

Return Duct

The central heating or cooling system contains a fan that gets its air supply through these ducts, which ideally should be installed in every room of the house. The air from a room will move towards the lower pressure of the return duct.

Reversing Valve

A device in a heat pump that is electrically controlled to reverse the flow of refrigerant as the system is switched from cooling to heating; also called a four-way valve.



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.

Scroll Compressor

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

Single Package

One outdoor unit that contains both a heating and a cooling system.

Smart Recovery

Smart Recovery starts the system in advance to be sure that each zone reaches your selected temperature setting at the scheduled time.

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).

Supply Duct

HVAC term for the duct(s) of a forced air heating/cooling system through which heated or cooled air is supplied to rooms by the action of the fan of the central heating or cooling unit.


Tankless Water Heater

A water heater that heats waters before it is directly distributed for end use as required; a demand water heater.


A unit of heat containing 100,000 BTU


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.


A unit of measure for cooling capacity. One ton = 12,000 BTUs per hour.



A type of furnace that draws cool air from the bottom and blows the warmed air out the top into the duct work. This type of furnace is usually installed in a basement or an out-of-the-way closet.



A component of a heating or ventilation appliance used to conduct fresh air into or waste air out of an appliance or interior space

Vent Damper

An HVAC term for a device mounted in the vent connector that closes the vent when the heating unit is not firing. This traps heat inside the heating system and house rather than letting it draft up and out of the vent system.



A way to increase your home comfort and energy efficiency by controlling when and where heating and cooling occurs in a home. Programmable thermostats are used to control operating times of the equipment. Dampers are used to direct air flow to certain parts or "zones" of the home.