Boulder HVAC glossary of terms

Terms and technical definitions for Boulder HVAC including heating, cooling and indoor air quality products.


Annualized Fuel Utilization Efficiency is 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%.


The distribution or movement of air.

Air-Conditioning and Refrigeration Institute (ARI)

ARI is an industry trade association that develops standards for measuring and certifying product performance. For instance, ARI Standard 270 provides guidelines for establishing sound levels for outdoor air-conditioning equipment.

Air Handler/Coil Blower

The indoor part of an air conditioner or heat pump that moves cooled or heated air throughout the ductwork of your building. An air handler is usually a furnace or a blower coil.


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


A British thermal unit is a unit of heat energy. One Btu is the amount of heat required to raise one pound of water by one degree Fahrenheit. The higher the Btu rating, the greater the heating capacity of the system.


British thermal units per hour.


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 Monoxide

An odorless, colorless, tasteless, poisonous and flammable gas that is produced when carbon burns with insufficient air.

Central Air Conditioning System

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


Stands for Cubic Feet per Minute. This measurement indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being moved through the ductwork by the system.

Composite Fan Blades

Used in select Lennox outdoor air conditioner or heat pump units, blades are manufactured with rugged materials and an exclusive angled design that improve operation and durability, even in the harshest environments.


The part of the outdoor air conditioner or heat pump that compresses and pumps refrigerant to meet household cooling requirements.

Condenser Coil

The outdoor portion of an air conditioner or heat pump that either releases or collects heat, depending on the time of the year.


A movable plate, located in the ductwork, that regulates airflow. Dampers are used to direct air to the areas that need it most. Typically used in a zoning application.


A decibel is a unit used to measure the relative intensity of sound.


The Department of Energy is a federal agency responsible for setting industry efficiency standards and monitoring the consumption of energy sources.

Dry-charged unit

An air-conditioner or heat pump that is shipped dry and charged with refrigerant at the place of installation. Dry-charged units are appropriate for homeowners who need a replacement unit compatible with R-22 refrigerant.

Dual Fuel

A comfort system that pairs an electric heat pump with a gas furnace, providing an energy-efficient alternative to the conventional furnace/air conditioner combination.


The method by which air is channeled from the furnace or the blower coil throughout your building.

Electronic Air Cleaner

An electronic device that filters out large particles and bioaerosols in indoor air.


An EPA (Environmental Protection Agency) designation attached to HVAC products that meet or exceed EPA guidelines for high-efficiency performance above the standard government minimums.


The Environmental Protection Agency develops and enforces federal environmental regulations. The EPA oversees the nationwide ENERGY STAR® program.

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 building.


Stands for “frequently asked questions.”

Heat Exchanger

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

Heat Pump

A heat pump is an HVAC unit that heats or cools by moving heat. During the winter, a heat pump draws heat from outdoor air and circulates it through your building’s air ducts. In the summer, it reverses the process and removes heat from your building and releases it outdoors.

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.


The Heating Seasonal Performance Factor is the heating efficiency rating for heat pumps. The higher the rating, the more efficient the heat pump. HSPF will be regulated in 2006 at 7.7.


An indoor air quality device that introduces moisture to heated air as it passes from the furnace into the ductwork for distribution throughout the building.


An automatic device used to maintain humidity at a fixed or adjustable set point.


Heating, Ventilation and Air Conditioning.

Indoor Coil

See Evaporator Coil.

ISO 9000

A family of international standards for quality management and assurance.

MERV Rating

The MERV (Minimum Efficiency Reporting Value) rating of a filter describes the size of the holes in the filter that allow air to pass through. The higher the MERV rating, the smaller the holes in the filter, the higher the efficiency.


A unit of measure equal to one millionth of a meter, or one thousandth of a millimeter.


Air contaminants in the form of gases.

Outdoor Coil

See Condenser Coil.


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.

Programmable Thermostat

A thermostat with the ability to record different temperature/time settings for your heating and/or cooling equipment.

R-22 Refrigerant

The old standard for residential air conditioners, R-22 refrigerant is now being phased out by the U.S. EPA. Lennox offers dry-charged units for those who still have R-22 compatible systems.

R-410A Refrigerant

A chlorine-free refrigerant that meets the EPA’s newest, most stringent environmental guidelines.


A chemical that produces a cooling effect while expanding or vaporizing. Most commercial / industrial air conditioning units contain the standard R-22 refrigerant, or Freon.

Refrigerant Lines

Two copper lines that connect the outdoor air conditioner or heat pump to the indoor evaporator coil.

Scroll Compressor

A specially designed compressor that works in a circular motion, as opposed to up-and-down piston action.


The Seasonal Energy Efficiency Ratio is an energy efficiency rating for air conditioners. The higher the SEER, the better the energy performance, the more you save. The DOE’s established minimum SEER rating for cooling is 13.00.

Single Package

A heating and cooling system contained in one outdoor unit.

Split System

An HVAC system in which some components are located inside the structure of the building and some are located outside. Split systems should be matched for optimal efficiency.


Monitors temperature and humidity and adjusts heating or cooling system to maintain desired levels.


Usually found on an inside wall, this device operates as a control to regulate your heating and cooling equipment, allowing you to adjust your home comfort at the touch of a switch.


Unit of measurement for determining cooling capacity. One ton equals 12,000 Btuh.

Two-Stage Operation

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


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.

Variable Speed Motor

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


A system that exchanges stale, recirculated indoor air with fresh, filtered outside air.


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

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