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Glossary of Terms

This Glossary of Terms is intended for use in context with this website. Other definitions for these terms may also be relevant when used in a different context. The HVAC terms are courtesy of Lennox, and the plumbing terms are courtesy of PBS.


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 home. 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.

Communication Module

A component of a SunSource® Home Energy System, a communication module allows you to view system status and environmental benefits in real time.

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 home.

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 house.


Stands for “frequently asked questions.”

Garage Heaters

Garage heaters are an excellent product for combating cold garages and workshops during the winter months. Heating capacities provide warmth for a 1 car garage up to a 4+ 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.


A grid-tied system is the most common and least expensive of all residential solar systems. It allows you to use your own solar-generated electricity to save energy and reduce costs. At times when the solar system isn’t producing electricity, such as at night, electricity is provided by the utility company’s grid, or network of power stations.

Heat Exchanger

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

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 home’s air ducts. In the summer, it reverses the process and removes heat from your house 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 home.


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


Heating, Ventilation and Air Conditioning.


Refers to products from the Dave Lennox Signature® Collection of heating, cooling and humidity control products that are configured to work with the iComfort Wi-Fi® programmable thermostat as an advanced home comfort system.

iComfort by Lennox® System

Lennox’ most advanced heating, cooling and humidity-control products synchronize with the iComfort Wi-Fi® thermostat to deliver maximum comfort, performance and efficiency.

Indoor Coil

See Evaporator Coil.

Interconnection Agreement

See “net metering.”

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.

Net Metering

With this service, which is available from many utility providers, you can get full retail value for most, if not all, of the electricity produced by your own generating system, such as a SunSource® Home Energy System. Your utility meter keeps track of the “net” difference between the electricity you use from your utility provider and the electricity you produce with your own system.


Air contaminants in the form of gases.

Off-grid or Off-the-grid

An off-grid electricity-generating system operates independently from the utility grid, providing all of the electricity needed in the home. Stand-alone systems are much more expensive than grid-tied systems. However, for homes located in remote areas without utility service, or where installing power lines would be extremely costly, a stand-alone system is a good option.

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 residential 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.

SilentComfort™ Outdoor Fan Motor

Used in select Lennox outdoor air conditioner or heat pump units, the fan motor is designed with innovative electronic sensor technology that helps optimize overall system performance while keeping sound levels low.

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 house and some are located outside. Split systems should be matched for optimal efficiency.

Solar Module

A component of a SunSource® Home Energy System, solar modules mount on the roof to harness solar power to reduce heating and cooling costs.

Solar Ready

A term used with select air conditioners and heat pumps from the Dave Lennox Signature® Collection, “solar ready” means the systems can be integrated with solar modules in a SunSource® Home Energy System.


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


Acrylonitrile-butadiene-styrene. Used for drain and vent lines.


The system of screens screwed into the spout of most faucets. The aerator helps control the flow of water and keep it from splashing all over. They frequently contain a baffle to help reduce the flow of water to the mandated 2.5 gallons per minute.

Air Admittance Valve (AAV)

A device that replaces a traditional vent to allow air to enter the pipe and equalize pressure, preserving the seal of water in the fixture trap.


In the drainage system, the unobstructed vertical opening between the lowest opening of a waste line and the flood level of the device into which it empties. Purpose is to prevent backflow contamination.

Anti-scald Valve

See Pressure-balancing Valve

Backflow Preventer

A device that prevents wastewater and other contaminants from flowing into the potable water supply. Generally required for sprinkler systems, hand-held showers installed in bathtubs, faucets with pullout spouts, kitchen sprayers, and the like.


A valve operated by a float, such as a floatball or a float-cup in a toilet tank.


Any part of the drain system other than the main, riser, or stack.


A pipe fitting used to join two pipes of different sizes. A bushing is threaded inside and out.

Check Valve

A type of backflow preventer installed in a pipe run that allows water to flow in only one direction.


A pipe fitting with a removable plug for inspecting and cleaning out drain pipes.

Closet Bend

The curved section of drain pipe located immediately below the toilet.

Closet Flange

A round, flat fitting that attaches to the closet bend. The heads of closet bolts, used to secure the toilet in place, insert into slots in the closet flange.


A short fitting used to join two pieces of pipe.


Chlorinated polyvinyl chloride. Used for water supply.


Any connection or situation that may allow waste water to enter the supply system.


Any pipe that carries wastewater or water-borne waste.


Drainage, waste, and vent.


Curved fittings, usually 90 degree or 45 degree, used to change the direction of a pipe run. Also called “ells.”


A decorative or protective plate. In plumbing, the plate behind or under a fixture that covers the hole around the pipe or valve.


Any pipe part used to join together two sections of pipe, such as elbows, couplings, bends, wyes, etc.


Accepts or discharges water or wastewater, such as faucets, sinks, toilets, etc.

Flapper Valve

The part on the bottom of the toilet tank that opens to allow water to flow from the tank into the bowl.

Float Ball

In the toilet tank, the hollow ball attached to a rod that rises as the tank refills and shuts the water inlet valve.


Substance applied to copper pipes and fittings before soldering to help the fusion process and prevent oxidation.


Device used to support pipes.

Hose Bibb

An outdoor faucet, also used to supply washing machines.


Industry term for bathroom sink.


The primary artery of the supply or drain system to which all the branches connect. Referred to as the Main Vent in the vent system.


A fitting that connects a number of branches to the main; serves as a distribution point.


A short length of pipe installed between couplings or other fittings.

No-hub Connector

A connector for no-hub iron pipe consisting of a rubber sleeve and a stainless-steel band secured by hose clamps. A variation, a neoprene sleeve with two adjustable steel bands, is used for connecting dissimilar materials, as when connecting new plastic pipe to an existing cast-iron drain pipe.


The packing material used before sealing a hubbed cast-iron fitting with lead.


Cross-linked polyethylene. PEX tubing, commonly used for hydronic radiant floor heat, is increasingly used for water supply lines.

Pipe Dope

Slang for pipe-joint compound. Substance applied to threaded fittings to create a watertight seal.


Water that suitable for consumption.

Pressure-balancing Valve

A mixing valve that monitors the water pressure in both the hot and cold supply lines and compensates for a drop in either one.


Polyvinyl chloride. Used for drain and vent lines.


A fitting that allows pipes of different sizes to be joined together.

Relief Valve

A valve that opens to relieve excess temperature and/or pressure in the system. See T&P Valve.


A supply line pipe that rises from one story to the next; also the short vertical pipes that bring water from the branch to the fixture.


Installation of the drain, vent, and supply lines in the structure prior to installation of the fixtures.

Shutoff Valve

Most commonly refers to the angle stops installed under sinks and toilets, but valves are also installed on branch lines and alongside the meter.


Another name for hose bibb.


A metal alloy that is melted to create a fused joint between metal pieces.


The vertical main in the DWV system extending one or more stories.


The shutoff valves under sinks and toilets.


Short lengths of pipe installed during rough-in to which fixtures and drains will eventually be installed.


Slang for soldering.


The eased change of direction in a drain fitting that allows for smooth passage of waste. Fittings with abrupt changes of direction, such as a vent tee, may only be used for vents.

T&P Valve

Temperature and pressure valve. A valve that opens to release excess pressure and temperature in a system.


The section of pipe that runs between a fixture outlet and the trap.

Tee Fitting

Fittings that allow another pipe to be joined at a 90-degree angle. Those for the drain system have the changes of direction eased. See Sweep.


A fitting or portion of a fixture that, when properly vented, holds water to prevent entry of sewer gases.


A device that regulated the flow of water.

Valve Seat

The immovable portion of a valve. Water flow is stopped when the movable portion of the valve comes in contact with the valve seat.


A pipe that allows air into a drain system to balance the air pressure, preventing the water in the traps from being siphoned off.

Water Hammer Arrestor

A device installed near a fixture to absorb the hydraulic shock that happens when a fixture’s supply is suddenly shut off, causing water hammer, a loud banging noise in the pipes.

Wye Fitting

A drain fitting that allows one pipe to be joined to another at a 45-degree angle.