As the energy industry grows and evolves, so does its terminology. To understand any industry, you need to know the language. This glossary offers useful terms and definitions to help you understand more about the energy industry.


Annual Fuel Utilization Efficiency. Refers to the ratio of annual output of useful energy to the annual energy input to the furnace. The higher the AFUE, the more efficient the furnace.

Air Barrier

A continuous surface designed to block the flow of air.

Air Conditioning – Cooling

A term associated with the summer cooling of indoor air.


The process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems. Proper balancing is performed using accurate instrumentation to deliver the right amount of heating or cooling to each area or room of the home.


A device to heat water, which is then used to condition the spaces of a building.


British Thermal Unit. The quantity of heat required to raise the temperature of 1 lb. of water 1° F.

Central Forced-Air Heating System

A piece of equipment that produces heat in a centralized area, then distributes it throughout the home through a duct system.

Conditioned Space

An enclosed space that is mechanically heated and/or cooled.


The orientation of the furnace and the direction of airflow through it. A furnace may have an upflow, downflow or crossflow (horizontal) configuration.


Compact Fluorescent Light

Saving energy is easy when you replace regular incandescent bulbs with CFL’s. Compared to standard bulbs, CFL’s use 75% less energy, last 10 times longer, give off bright, pleasant light, come in lots of shapes and sizes.


The amount of electricity or natural gas used by, or delivered to, a household during a 365-day period.


Critical Peak Pricing (CPP) is designed to reward customer who are willing to reduce their energy consumption during critical peak hours. CPP complements Power Response.


A device that is located in ductwork to adjust air flow. There are two types of dampers: manual and motorized. A manual damper generally consists of a sheet metal flap, shaped to fit the inside of a round or rectangular duct. By rotating a handle located outside of the duct, a technician can adjust air flow to match the needs of a particular are or room. A motorized damper is generally used in a zoned system to automatically deliver conditioned air to specific rooms or zones.


Demand-side Management (DSM) encourages customers to control their electricity usage. It includes opportunities for conservation, energy efficiency, load shifting and peak-shaving activities.


The delivery system through which conditioned air is sent throughout the home and returned to the heating and cooling system. Ductwork is made of sheet metal, fiberglass, or flexible plastic, and can be round or rectangular in shape.


You can view and pay your Dominion bill online with eBill, a convenient paperless billing solution.


The rate at which a furnace maximizes fuel use. This rate is numerically described as a ratio called AFUE (see AFUE). As of January, 1992, no furnaces can be manufactured with efficiencies lower than 78 percent AFUE. High-efficiency furnaces will be rated 88 to 97 percent AFUE. See also SEER and HSPF for efficiency ratings for heat pump systems.

Electronic Ignition

A device that eliminates the need for a continuously burning pilot. These and many other features let the mid-efficiency furnace satisfy your heating needs with less energy than your existing furnace.

Energy Efficiency

Using less energy/electricity to perform the same function.


Energy Efficiency Rating

The cooling efficiency of an air condition in an exact set of conditions. The higher the EER rating, the more efficient the unit.

Forced Air

A type of heating system that uses a blower motor to move air through the furnace, into the ductwork, and into the living area.


Refers to a wide variety of heating systems incorporating a blower and heating unit, which is either connected to an air distribution system or may blow directly into the space to be heated.

Heat Exchanger

Enables furnaces to safely transfer heat from combustion into breathable air. The primary heat exchanger transfers heat from combustion gases to the air blowing through the ductwork, never allowing combustion gas into the air stream. The primary heat exchanger handles the hottest gases. In high-efficiency furnaces, secondary heat exchangers recover heat that used to be vented up the chimney with the exhaust gases. By recovering this heat, the furnace becomes more efficient.

HSPF - Heating Seasonal Performance Factor

Heating Seasonal Performance Factor

HSPF is one of two energy efficiency ratings for heat pump systems (SEER is the other). The HSPF rating measures operating efficiency during the heating season. The higher the HSPF rating, the more efficiently the system will perform.


Heating, Ventilation, and Air Conditioning

Hydronic Heating

System that delivers heat from water heated by a boiler to baseboard fintube or to another style of water-to-air heat exchanger.

Kilowatt (kW)

1,000 watts

Kilowatt hour (kWh)

The unit used to meter electricity. 1 kilowatt used for one hour = 1 kilowatt hour.

Power Response

Power Response encourages customers to control their electricity usage, including opportunities for conservation.


R-value is a measure of how well insulation will resist the flow of heat. Higher R-values mean greater insulating ability, which means greater household energy savings and greater cost savings.

Renewable Energy

Renewable energy, or green power, is power that comes from renewable resources such as the sun, wind, hydroelectric dams, and organic matter (biomass). These resources are constantly replenished by nature and are a cleaner source of energy. Using renewable resources to generate energy reduces the carbon dioxide, nitrogen oxide and sulfur dioxide released in the air through more traditional generation.


Seasonal Energy Efficiency Rating

SEER is an energy efficiency rating for heat pump systems. The SEER rating measures operating efficiency during the cooling season. The higher the SEER rating, the more efficient the system will perform. SEER is also used to rate central air-conditioning systems.


The procedure a heating contractor uses to determine the proper system size needed to heat and/or cool a home efficiently. For instance, a system that is sized too small won't deliver enough heat, while a system sized too large increases energy costs and can have an adverse effect on comfort. Sizing depends on the square-footage of the home, the amount of ceiling and wall insulation, the window area, use of storm doors, storm windows, and more.


A measurement of heat. One therm equals 100,000 BTUs.


The Time-of-Use rate (TOU) is designed to reward customers who are willing to reduce their energy consumption during on-peak hours. TOU complements Demand-side Management (DSM).

Vapor Barrier

Any material, typically a plastic or foil sheet, that resists passage of moisture through wall, ceiling and floor assemblies of buildings.


Electricity is measured in watts. Wattage quantifies electrical current usage with both voltage and amperage.

Zone Control

A system in which living areas are divided into separate spaces and the heating/air conditioning is controlled independently. This can be accomplished by using either multiple independent systems, or a single system using electronic controls and motorized dampers (see Damper).

Environment  We’ve got a “green thumb” too! This icon indicates a message that promotes awareness about our environmental programs or provides you with information that helps you save energy, save money and live life a little greener.
NYSE : (April 24, 2014) D 71.55 0.49