Common Industry Terminology

On this page you will find definitions about various terms used within this website.  Terms are listed in alphabetical order.

• AFUE - Acronym for Annual Fuel Utilization Efficiency.  AFUE is the most widely used measure of a furnace's or boiler's heating efficiency.  It measures the amount of heat actually delivered to your house compared to the amount of fuel that you must supply to the furnace.  AFUE refers only to the unit's fuel efficiency, not its electricity usage.
• Air Conditioning - The process of controlling the temperature, humidity, cleanliness, and distribution of the air.
• Air Handler - The indoor unit that circulates conditioned air throughout a building.  When matched with a heat pump, it circulates both cool and hot air, depending on the season.
• All-In-One System - A climate control system consisting of heating and cooling components that are housed in a single cabinet.
• BTU - Acronym for British Thermal Unit.  The amount of heat necessary to change the temperature of 1 pound of pure water 1 degree Fahrenheit.
• Capacity - The ability of a heating or cooling system to heat or cool a given amount of space.  Heating is usually expressed in BTUs and cooling in tons.
• Compressor - A mechanical device used to compress gases.  There are three main types of compressors.  Reciprocating, centrifugal, and rotary.
• Condenser Coil - Part of the outdoor portion of a heating or cooling system, that releases or collects heat from the outside air.
• Damper - A valve or moveable plate used in ductwork that opens and closes to control airflow.  They are used to direct air to specific areas of the home.
• Downflow - A type of furnace that takes cool air from the top and blows warm air to the bottom.
• Ductwork - Hollow metal pipes used to transfer air throughout a building.
• Electronic Air Cleaner - An electronic device that filters out particles and contaminants in indoor air.
• Energy Star - A United States government program to promote energy efficient consumer products.
• EPA - Acronym for Environmental Protection Agency.  The EPA is an agency of the federal government of the United States charged with protecting human health and with safeguarding the natural environment: air, water, and land.
• Evaporator - A device in which a liquid refrigerant is vaporized.  Some superheating usually takes place.
• 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.
• Green Building - The practice of increasing the efficiency with which buildings and their sites use and harvest energy, water, and materials, and reducing building impacts on human health and the environment, through better siting, design, construction, operation, maintenance, and removal.  The complete building life cycle.
• Heat Exchanger - The major part of a furnace that transfers heat into a building.
• Heat Pump - A machine or device that moves heat from one location to another.
• Horizontal Flow - A type of furnace, installed on its side, which draws air from one side, heats the air, and then sends it out the other side.
• HSPF - Acronym for Heating Seasonal Performance Factor.  Measures the heating efficiency of a heat pump. The higher the number the more efficient the heat pump heats a building.
• Humidifier - A piece of equipment that adds moisture to the air as it comes out of a furnace.  Stand-alone humidifying units (humidifiers) are also available.
• HVAC - Acronym for Heating, Ventilation and Air Conditioning.
• IEQ - Acronym for Indoor Environmental Quality.  IEQ refers to the quality of the air and environment inside buildings, based on pollutant concentrations and conditions that can affect the health, comfort and performance of occupants.
• MERV - Acronym for Minimum Efficiency Reporting Value, and is a measure of a filter's worst-case efficiency performance.  The higher the MERV rating, the more efficient the filter.
• 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.
• NOx - A generic term for mono-nitrogen oxides. These oxides are produced during combustion, and are of interest as air pollution.  They are believed to aggravate asthmatic conditions, react with the oxygen in the air to produce ozone, which is also an irritant, and eventually form nitric acid when dissolved in water.  When dissolved in atmospheric moisture the result can be acid rain which can damage both trees and entire forest ecosystems.
• Puron - Brand name of an ozone-friendly chlorine-free refrigerant by DuPont.
• Superheating (sometimes referred to as boiling retardation, or boiling delay) - The phenomenon in which a liquid is heated to a temperature higher than its standard boiling point, without actually boiling.
• Refrigerant - A compound used in a heat cycle that undergoes a phase change from a gas to a liquid and back.  The two main uses of refrigerants are refrigerators/freezers and air conditioners.
• RH - Acronym for Relative Humidity.  Relative humidity is defined as the ratio of the partial pressure of water vapor in a gaseous mixture of air and water vapor to the saturated vapor pressure of water at a given temperature.  Relative humidity is expressed as a percentage.
• SEER - Acronym for Seasonal Energy Efficiency Ratio, used to rate the efficiency of air conditioners.
• Spine Fin Coil -  An outdoor air conditioning coil that consists of tubes and fins that are bonded together allowing for faster heat transfer.  This type of coil has greater air-to-fin surface area which leads to higher efficiency and lower energy usages.  The tiny spines of this type coil has the advantage of resisting clogging by sand, salt, leaves, ice and other debris.
• Split System - Refers to an air conditioner or heat pump that is combined with indoor components, such as an evaporator coil inside and a condenser coil outside of a building.
• Setback Thermostat - A state-of-the-art electronic thermostat with a built-in memory that can be programmed for different temperature settings at different times of the day.
• Thermostat - A device that monitors and controls the temperature inside of a building.
• Ton - A unit of measure for cooling capacity.  One ton = 12,000 BTUs per hour.
• Upflow - A type of furnace that draws cool air from the bottom and blows the warmed air out the top.
• UV - Acronym for Ultraviolet.  UV Light is used in the HVAC industry to kill airborne microorganisms.
• Ventilator - A ventilator captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.
• Zoning - The ability to independently by room (zones) air comfort.  A forced air system uses a control panel and motorized dampers working in separate trunk lines to make comfort zones.  A hot water system uses zone valves or circulators feeding individual loops to form individual comfort zones.