Hvac Terminology

AC, A.C. or Ac may refer to: Air conditioning, technologies for altering the temperature and humidity of air; Alternating current, a type of electrical current in which the current repeatedly changes direction.

Air-Conditioning Contractors of America.

A heat exchanger (evaporator coil) consisting of two diagonal coils that are joined together in a manner that looks like the letter “A”.

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

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.

Abbreviation for American Gas Association, Inc.

Air Conditioning, Heating & Refrigeration Institute

Removes airborne allergens from your home.

Any device that can change the temperature, humidity or general quality of the air. More specifically, an air conditioner makes your home cooler, by drawing heat energy out of the house and transferring that heat to the outdoors

The amount of air the system circulates through your home, expressed in cubic feet per minute (cfm). Proper air flow depends on the outdoor unit, the indoor unit, the ductwork and even whether the filters are clean.

An air moving and/or mixing unit. Residential air handlers include a blower, a coil, an expansion device, a heater rack and a filter. Heaters for air handlers are sold as accessories. In some models, heaters are factory installed. The portion of your heating and cooling system that forces air through your home’s ductwork.

American Society of Heating, Refrigeration and Air Conditioning Engineers- ASHRAE is an international voluntary organization for people involved in heating, ventilation, air conditioning, or refrigeration (HVAC&R).

The society promotes the general sciences of HVAC&R. The main Society headquarters is located in Atlanta, Georgia with local chapters located across the United States and throughout the world.

ASHRAE publishes a four-volume Handbook that serves as a resource for members, with one of the four volumes updated each year. ASHRAE also publishes a well recognized series of standards and guidelines relating to HVAC Systems. ASHRAE Standards are often referenced in other model building codes and in the US Green Building Council’s Leadership in Energy Design (LEED) green building rating system.

British thermal unit; the amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit. The heat extracted from your home by an air conditioner is measured in BTUs.

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

A device that uses fuel to support combustion.

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

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

Provides the number of cubic feet of clean air that a unit delivers each minute. Efficiency of the system times the airflow of the system.

The output or producing ability of cooling or heating systems. Cooling and heating capacities are referred to in British thermal units (BTUs) per hour.

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).

The Air Conditioning, Heating and Refrigeration Institute (AHRI) puts heating and cooling equipment through rigorous certification processes to ensure systems deliver the promised performance at certain test conditions.

Abbreviation for cubic feet per minute, a standard measurement of airflow. A typical system requires 400 cfm of air flow per ton of air conditioning.

To add refrigerant to a system. This is refrigerant contained in a sealed system or in the sensing bulb to a thermostatic expansion valve.

Part of an indoor air unit, it functions with the air conditioner or heat pump outdoors to cool and condition indoor air that flows over it by drawing out heat and moisture.

This is the heart of an air conditioning or heat pump system. It is part of the outdoor unit and pumps refrigerant in order to meet the cooling requirements of the system.

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

Part of the outdoor portion of a heating or cooling system, which releases or collects heat from the outside air.

The fan that circulates air over the air-cooled condenser.

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

This is the electric resistance heater installed on compressor crankcases to boil off liquid refrigerant that may have combined with compressor oil. Many newer cooling systems do not require crankcase heaters, however heat pumps do require crankcase heaters.

Canadian Standards Association.

A unit to measure sound.

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

To melt frost (as in from an air conditioner or heat pump coil).

A degree-day is a computation that gauges the amount of heating or cooling needed for a building. A degree-day is equal to 65 degrees Fahrenheit minus the mean outdoor temperature.

An air cooler that removes moisture from the air.

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

Department of Energy

A furnace that intakes air at its top and discharges air at its bottom.

This is also referred to as a condensate pan. This is a pan used to catch and collect condensate (in residential system’s vapor is liquefied on the indoor coil, collected in the drain pan and removed through a drain line).

Heat intensity, measured by a dry bulb thermometer.

An instrument that measures air temperature independently of humidity.

An outdoor unit featuring two compressors, one for everyday cooling and a second larger one for extreme temperature days. Provides superior durability designed for cost-saving efficiency and low sound levels.

A pipe or conduit through which air is delivered. 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 important as the equipment.

Direct expansion; a system in which heat is transferred by the direct expansion of refrigerant.

Maytag’s designation of green heating and cooling equipment.

Energy Efficiency Ratio (steady state)

Electronically filters out magnetized airborne particles from contaminants in indoor air, sending them to a collector plate.

Environmental Protection Agency

Part of an indoor air unit, it functions with the air conditioner or heat pump outdoors to cool and condition indoor air that flows over it by drawing out heat and moisture.

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).

Any device that creates air currents.

Any device that removes impurities through a straining process.

Any vent or passageway that carries the products of combustion from a furnace.

That part of the heating system in which the combustion of fossil fuel and transfer of heat occurs.

A metal strip in an electrical circuit that melts and breaks the circuit when excessive current flows through it. The fuse is designed to break in order to save more expensive electrical components.

Gas Appliance Manufacturers Association

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

An area, box or coil where heat flows from the warmer to the colder fluid or surface. The major part of the furnace that transfers heat into your home.

Heat added to the conditioned space by infiltration, solar radiation, occupant respiration and lighting.

Any coil that serves as a heat source.

The rate of heat transfer from a heated space to the outdoors.

A mechanical-compression cycle refrigeration system that can be reversed to either heat or cool the controlled space.

The movement of heat energy from one point to another. The means for such movement are conduction, convection, and radiation.

Filter that traps airborne particles by forcing air through very dense mesh.

In alternating current (AC electricity), the number of cycles per second.

Often used in attics/crawl spaces, this furnace takes air from its side, heats it and sends warm air out the other side.

Heating Seasonal Performance Factor. This rating is used in measuring the heating efficiency of a heat pump. The higher the number, the more efficient the heat pump system.

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

A humidity-sensing control that cycles the humidifier on and off.

The presence of water vapor in the air.

Weight of water vapor per cubic foot of dry air, expressed as grains of moisture per cubic foot.

The amount of moisture in the air expressed as a percentage of the maximum amount that the air is capable of holding at a specific temperature.

Abbreviation for Heating, Ventilating and Air Conditioning.

Provides energy-efficient comfort for moderate heating conditions. Can use either gas or electricity.

This type of system provides energy-efficient comfort for moderate heating conditions. Depending on the weather and your comfort needs, it can use either gas or electricity, with an electric heat pump as the outdoor component and a gas furnace the indoor component.

The lighting of a fuel to make it burn.

Part of an indoor air unit, it functions with the air conditioner or heat pump outdoors to cool and condition indoor
air that flows over it by drawing out heat and moisture.

The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler).
Split systems must be matched for optimum efficiency.

The air conditioner and heat pump utilize inverter technology compressors to convert the electrical current from
AC to DC. In doing so, the systems almost infinitely vary the compressor and fan speed motors. The air
conditioner and heat pump can modulate anywhere from 40% to 100% of capacity, instantly adjusting to exactly
offset the demands on the home. Because these units do not cycle on and off like a traditional system, they save
a considerable amount of energy and reduce noise levels.

1,000 watts

Assessed by a dealer, the calculation factors in a number of criteria in your home (square footage, number of windows, year-round weather concerns) and determines what size components you should include as part of your total comfort system.

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

The material in a filter that traps and holds the impurities.

North American Technician Excellence—certification acknowledging a dealer/technician as one of the most knowledgeable and experienced at installing and servicing high-performance, precision-engineered heating and cooling systems.

National Energy Council / National Electric Code

National Electrical Manufacturing Association

Original Equipment Manufacturer

Cost of running your home comfort system, based on energy usage

An opening or hole; an inlet or outlet

In a heat pump, it takes in heat to warm your home. In an air conditioner, it dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid to cool your home.

A single cabinet, typically installed outside, that houses both heating and cooling components.

A single cabinet, typically installed outside, that houses both

Number of years required before your monthly energy savings offset the original HVAC investment.

Pounds per square inch.

Per square inch, absolute.

Pounds per square inch gauge.

Polyvinyl chloride; a type of plastic.

A compressor whose piston or pistons move back and forth in the cylinders.

Returning used refrigerant to the manufacturer for disposal/reuse.

Removing, cleaning and reusing refrigerant.

The required amount of refrigerant in a system.

Two copper lines connecting the outdoor condenser to the indoor evaporator coil.

Seasonal Energy Efficiency Ratio; a measure of cooling efficiency for air conditioners and heat pumps. The higher the SEER, the more energy efficient the unit.

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

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

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

The temperature or pressure at which a controller is set with the expectation that this will be a nominal value depending on the range of the controller.

All-aluminum outdoor coil that features the patented Spine Fin™ design. It provides greater heat-exchanging capabilities (meaning higher efficiencies) and is more resistant to corrosion than a traditional copper/aluminum coil.

The combination of an outdoor unit (air conditioner or heat pump) with an indoor unit (furnace or air handler).
Split systems must be matched for optimum efficiency.

A thermostat consists of a series of sensors and relays that monitor and control the functions of a heating and cooling system.

A refrigerant metering device that maintains a constant evaporator temperature by monitoring suction vapor superheat; also called a thermal expansion valve.

A unit of measurement used for determining cooling capacity. One ton is the equivalent of 12,000 BTUs per hour.

Compressor composed of a high and low stage to increase efficiency and comfort while reducing operation noise.

Two-stage heating and cooling is considered to be more efficient, because it operates at low speed most of the time. However, on days when more heating or air conditioning is required, it switches to the next stage for maximum comfort.

The factor representing resistance to heat flow of various building materials.

Underwriters Laboratories

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

A pressure below atmospheric pressure. A perfect vacuum is 30 inches of mercury (periodic symbol “Hg”)

The unit of measure used to describe a difference in electrical potential, abbreviated by the symbol “v.”

The force that pushes electrical current along wires and cables.

The unit of electrical power equal to the flow of one amp at a potential difference of one volt.

A thermometer whose bulb is covered with a piece of water-soaked cloth. The lowering of temperature that results from the evaporation of water around the bulb indicates the air’s relative humidity.

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

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