HVAC Glossary of Terms

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.

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.

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

Learn more about blower coils »

This is the amount of heat energy that can be converted into useful energy from a fuel, such as gas.

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

The blower is the portion of an HVAC system that pushes the filtered air from a return duct over the coil or heat exchanger. After the air is conditioned, the blower continues to direct the air into the supply ducts to be redistributed back into the home.

A boiler is a unit in which water or other fluid is boiled to generate heat. The heated or vaporized fluid can be used for various applications, including central heating. Though not as common nowadays in homes, boilers (and other steam heating systems) are among the most reliable on the market.

Learn more about boilers »

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.

An odorless, colorless, tasteless, poisonous, and flammable gas that is produced when carbon burns with insufficient air. It is toxic to humans and animals.

Learn more about carbon monoxide »

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.

Read more about central air conditioning systems »

A central heating system, much like a central air conditioning system, is an HVAC component that supplies heat through the entire building from one single source via a network of air ducts.

Learn more about central heating systems »

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.

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

Learn more about the compressor »

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.

Home dehumidifiers are installed to work in conjunction with your heating and cooling system. They draw warm, moist air through the return ductwork and cool it. When the air is cooled, moisture in the air condenses and turns into water droplets which fall into a collection pan or go directly down a drain. The dry air is passed over another set of coils so that it can reach the desired room temperature again before it’s circulated through your home.

Learn more about home dehumidifiers »

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

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.

Ductless HVAC is a great alternative to central heating and air conditioning systems. In fact, it works similarly to central heating and cooling except that it doesn’t require bulky ductwork. Your ductless mini-split system will have an indoor and outdoor unit, but it will only require a small hole to be cut through the exterior wall—just big enough for a tube of refrigerant to pass through. Inside your home, the air will be conditioned and returned to the room by the same unit.

Learn more about ductless HVAC systems »

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

Learn more about your HVAC ductwork »

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.

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.

Learn more about your AC evaporator coil »

Stands for “frequently asked questions.”

A forced air HVAC system is one where the heated or cooled air is pushed (or forced) by a fan over the coil or heat exchanger and into the supply ducts to be redistributed back into the building.

Learn more about forced air heating systems »

Fuel oil refers to any liquid petroleum product burned for the generation of heat in a furnace.

A furnace is a forced air HVAC system that heats the air in your home. Whether gas, oil, or electrical, the furnace works by blowing the air from the return ducts through the plenum and into the furnace itself to be heated. After the air has been heated, the blower fan pushes the air into the supply ducts to be returned back into the house.

Learn more about furnaces »

Garage heaters are an excellent product for combating cold garages and workshops during the winter months. Heating capacities provide warmth for a one-car garage up to a four+ car garage application. Separated combustion models provide heating for hard-to-heat applications. Available in natural or propane gas, units should be installed by a Lennox dealer/installer.

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

Learn more about your furnace heat exchanger »

The heat that escapes from the interior of the building into the outside air is known as heat loss. In order to improve energy efficiency, you want to minimize your home’s heat loss.

Learn more and find out how to prevent heat loss »

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 transfers it into the indoor air. In the summer, it reverses the process and removes heat from your house, and releases it outdoors.

Learn more about how a heat pump works »

Sometimes called “specific heat,” the heating capacity is the quantity of heat necessary to raise the temperature of a specific mass of substance (in the case of a furnace or heat pump, this would be air) by one degree.

This is the number of degrees per day that the daily average temperature is below a base temperature, often 65 degrees. HDD is used to determine indoor space heating requirements and heating system sizing.

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 home.

Learn more about whole-house humidifiers »

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

Heating, Ventilation and Air Conditioning.

Indoor air quality (IAQ) can be defined as the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants—and it can be affected by microbial contaminants (like mold and bacteria). Systems like air cleaners and humidifiers can help improve the indoor air quality of homes.

Learn more about our IAQ products »

See Evaporator Coil.

A family of international standards for quality management and assurance.

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.

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.

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

Learn more about programmable thermostats »

A chlorine-free refrigerant that meets the EPA’s newest, most stringent environmental guidelines. R-410A is a chlorine-free refrigerant—also known as Puron—that meets the EPA’s newest, most stringent environmental guidelines.

Learn more about the R-22 phase-out »

A chemical that produces a cooling effect while expanding or vaporizing. Most residential air conditioning units contain the standard R-22 refrigerant (which is being phased out) or R-410A.

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

The register is the vent connected to your ductwork, where the conditioned air is redistributed through the house.

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.

Learn more about SEER »

A heating and cooling system contained in one outdoor unit.

An HVAC system in which some components are located inside the structure of the house, 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, a thermostat operates as a control to regulate your heating and cooling equipment, allowing you to adjust your home comfort at the touch of a switch.

Learn more about our thermostats »

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

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.

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 home into independently controlled comfort zones for enhanced comfort and efficiency.

Learn more about zoning »