A device that moves and/or circulates air and provides ventilation for a room or a building.

Fan Coil

A heat exchanger coil in which a fluid such as water is circulated and a fan blows air over the coil to distribute heat or cool air to the different rooms.

Fan Velocity Pressure

The pressure corresponding to the outlet velocity of a fan; the kinetic energy per unit volume of flowing air.


A unit of electrical capacitance; the capacitance of a capacitor between the plates of which there appears a difference of 1 Volt when it is charged by one coulomb of electricity.


In a wind energy conversion system, to pitch the turbine blades so as to reduce their lift capacity as a method of shutting down the turbine during high wind speeds.

Federal Energy Management Program (FEMP)

A program of the U.S. Department of Energy (DOE) that implements energy legislation and presidential directives. FEMP provides project financing, technical guidance and assistance, coordination and reporting, and new initiatives for the federal government. It also helps federal agencies identify the best technologies and technology demonstrations for their use.

Federal Energy Regulatory Commission (FERC)

This is an independent regulatory agency within the U.S. DOE that has jurisdiction over interstate electricity sales, wholesale electric rates, natural gas pricing, oil pipeline rates, and gas pipeline certification. It also licenses and inspects private, municipal, and state hydroelectric projects and oversees related environmental matters.

Federal Power Marketing Administrations (PMA)

These are separate and distinct organizational agencies within the U.S. DOE that market power at federal multipurpose water projects at lowest possible rates to consumers consistent with sound business principles. There are five PMA’s: Alaska Power Administration, Bonneville Power Administration, Southeastern Power Administration, Southwestern Power Administration, Western Area Power Administration.


A power line for supplying electricity within a specified area.


A raw material that can be converted to one or more products.


The arrangement, proportion, and design of windows in a building.


The decomposition of organic material to alcohol, methane, etc., by organisms, such as yeast or bacteria, usually in the absence of oxygen.

Fiberglass Insulation

A type of insulation, composed of small diameter pink, yellow, or white glass fibers, formed into blankets or batts, or used in loose-fill and blown-in applications.


A coil of tungsten wire suspended in a vacuum or inert gas-filled bulb. When heated by electricity the tungsten “filament” glows.

Fill Factor

The ratio of a photovoltaic cell’s actual power to its power if both current and voltage were at their maxima. A key characteristic in evaluating cell performance.

Filter (air)

A device that removes contaminants, by mechanical filtration, from the fresh air stream before the air enters the living space. Filters can be installed as part of a heating/cooling system through which air flows for the purpose of removing particulates before or after the air enters the mechanical components.


A thin sheet of material (metal) of a heat exchanger that conducts heat to a fluid.


Both a noun and a verb to describe the exterior surface of building elements (walls, floors, ceilings, etc.) and furniture, and the process of applying it.

Fire Classification

Classifications of fires developed by the National Fire Protection Association.


A wood or gas burning appliance that is primarily used to provide ambiance to a room. Conventional, masonry fireplaces without energy saving features, often take more heat from a space than they put into it.

Fireplace Insert

A wood or gas burning heating appliance that fits into the opening or protrudes on to the hearth of a conventional fireplace.


The ability of a building construction assembly (partition, wall, floor, etc.) to resist the passage of fire. The rating is expressed in hours.


A wall to prevent the spread of fire; usually made of non-combustible material.

Firing Rate

The amount of BTUs/hour or kWs produced by a heating system from the burning of a fuel.

First Law of Thermodynamics

States that energy cannot be created or destroyed, but only changed from one form to another. First Law efficiency measures the fraction of energy supplied to a device or process that it delivers in its output. Also called the law of conservation of energy.

Fiscal Year (FY)

The U.S. Government’s 12-month financial year, from October to September, of the following calender year; e.g.: FY 1998 extends from Oct. 1, 1997 to Sept. 30, 1988.

Flame Spread Classification

A measure of the surface burning characteristics of a material.

Flame Spread Rating

A measure of the relative flame spread, and smoke development, from a material being tested. The flame spread rating is a single number comparing the flame spread of a material with red oak, arbitrarily given the number 100 and asbestos cement board with a flame spread of 0. Building codes require a maximum flame spread of 25 for insulation installed in exposed locations.

Flash-Steam Geothermal Plants

When the temperature of the hydrothermal liquids is over 350 F (177 C), flash-steam technology is generally employed. In these systems, most of the liquid is flashed to steam. The steam is separated from the remaining liquid and used to drive a turbine generator. While the water is returned to the geothermal reservoir, the economics of most hydrothermal flash plants are improved by using a dual-flash cycle, which separates the steam at two different pressures. The dual-flash cycle produces 20% to 30% more power than a single-flash system at the same fluid flow.


Metal, usually galvanized sheet metal, used to provide protection against infiltration of precipitation into a roof or exterior wall; usually placed around roof penetrations such as chimneys.


The minimum temperature at which sufficient vapor is released by a liquid or solid (fuel) to form a flammable vapor-air mixture at atmospheric pressure.

Flat-Black Paint

Nonglossy paint with a relatively high absorptance.

Flat Plate Solar Thermal/Heating Collectors

Large, flat boxes with glass covers and dark-colored metal plates inside that absorb and transfer solar energy to a heat transfer fluid. This is the most common type of collector used in solar hot water systems for homes or small businesses.

Flat Plate Solar Photovoltaic Module

An arrangement of photovoltaic cells or material mounted on a rigid flat surface with the cells exposed freely to incoming sunlight.

Flat Roof

A slightly sloped roof, usually with a tar and gravel cover. Most commercial buildings use this kind of roof.

Float-Zone Process

In reference to solar photovoltaic cell manufacture, a method of growing a large-size, high-quality crystal whereby coils heat a polycrystalline ingot placed atop a single-crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes a single crystal.


The upward facing structure of a building.

Floor Space

The interior area of a building, calculated in square feet or meters.

Flow Condition

In reference to solar thermal collectors, the condition where the heat transfer fluid is flowing through the collector loop under normal operating conditions.

Flow Restrictor

A water and energy conserving device that limits the amount of water that a faucet or shower head can deliver.


The structure (in a residential heating appliance, industrial furnace, or power plant) into which combustion gases flow and are contained until they are emitted to the atmosphere.

Flue Gas

The gas resulting from the combustion of a fuel that is emitted to the flue.


The practice of installing blow-in, loose-fill insulation at a lower density than is recommended to meet a specified R-Value.

Fluidized Bed Combustion (FBC)

A type of furnace or reactor in which fuel particles are combusted while suspended in a stream of hot gas.

Fluorescent Light

The conversion of electric power to visible light by using an electric charge to excite gaseous atoms in a glass tube. These atoms emit ultraviolet radiation that is absorbed by a phosphor coating on the walls of the lamp tube. The phosphor coating produces visible light.

Fly Ash

The fine particulate matter entrained in the flue gases of a combustion power plant.

Flywheel Effect

The damping of interior temperature fluctuations by massive construction.

Foam (Insulation)

A high R-value insulation product usually made from urethane that can be injected into wall cavities, or sprayed onto roofs or floors, where it expands and sets quickly.

Foam Board

A plastic foam insulation product, pressed or extruded into board-like forms, used as sheathing and insulation for interior basement or crawl space walls or beneath a basement slab; can also be used for exterior applications inside or outside foundations, crawl spaces, and slab-on-grade foundation walls.

Foam Core Panels

A type of structural, insulated product with foam insulation contained between two facings of drywall, or structural wood composition boards such as plywood, waferboard, and oriented strand board.

Foot Candle

A unit of illuminance; equal to one lumen per square foot.

Foot Pound

The amount of work done in raising one pound one foot.


The push or pull that alters the motion of a moving body or moves a stationary body; the unit of force is the dyne or poundal; force is equal to mass time velocity divided by time.

Forced Air System or Furnace

A type of heating system in which heated air is blown by a fan through air channels or ducts to rooms.

Forced Ventilation

A type of building ventilation system that uses fans or blowers to provide fresh air to rooms when the forces of air pressure and gravity are not enough to circulate air through a building.


A chemical used as a preservative and in bonding agents. It is found in household products such as plywood, furniture, carpets, and some types of foam insulation. It is also a by-product of combustion and is a strong-smelling, colorless gas that is an eye irritant and can cause sneezing, coughing, and other health problems.

Fossil Fuels

Fuels formed in the ground from the remains of dead plants and animals. It takes millions of years to form fossil fuels. Oil, natural gas, and coal are fossil fuels.


The supportive structure of a building.

Fractional Horse Power Motor

An electric motor rated at less than one horse power (hp).

Frame (Window)

The outer casing of a window that sits in a designated opening of a structure and holds the window panes in place.


The structural materials and elements used to construct a wall.

Francis Turbine

A type of hydropower turbine that contains a runner that has water passages through it formed by curved vanes or blades. As the water passes through the runner and over the curved surfaces, it causes rotation of the runner. The rotational motion is transmitted by a shaft to a generator.


The number of cycles through which an alternating current passes per second; in the U.S. the standard for electricity generation is 60 cycles per second (60 Hertz).


A registered trademark for a cholorfluorocarbon (CFC) gas that is highly stable and that has been historically used as a refrigerant.

Fresnel Lens

An optical device for concentrating light that is made of concentric rings that are faced at different angles so that light falling on any ring is focused to the same point.

Friction Head

The energy lost from the movement of a fluid in a conduit (pipe) due to the disturbances created by the contact of the moving fluid with the surfaces of the conduit, or the additional pressure that a pump must provide to overcome the resistance to fluid flow created by or in a conduit.


Any material that can be burned to make energy.

Fuel Cell

An electrochemical device that converts chemical energy directly into electricity.

Fuel Efficiency

The ratio of heat produced by a fuel for doing work to the available heat in the fuel.

Fuel Grade Alcohol

Usually refers to ethanol to 160 to 200 proof.

Fuel Oil

Any liquid petroleum product burned for the generation of heat in a furnace or firebox, or for the generation of power in an engine. Domestic (residential) heating fuels are classed as Nos. 1, 2, 3; Industrial fuels as Nos. 4, 5, and 6.

Fuel Rate

The amount of fuel necessary to generate one kilowatt-hour of electricity.

Full Sun

The amount of power density in sunlight received at the earth’s surface at noon on a clear day (about 1,000 Watts/square meter).


Plant-like organisms with cells with distinct nuclei surrounded by nuclear membranes, incapable of photosynthesis. Fungi are decomposers of waste organisms and exist as yeast, mold, or mildew.


The process of forcing, either manually or automatically, a wind turbine’s blades out of the direction of the wind in order to stop the blades from turning.

Furnace (Residential)

A combustion heating appliance in which heat is captured from the burning of a fuel for distribution, comprised mainly of a combustion chamber and heat exchanger.


A safety device consisting of a short length of relatively fine wire, mounted in a holder or contained in a cartridge and connected as part of an electrical circuit. If the circuit source current exceeds a predetermined value, the fuse wire melts (i.e. the fuse ‘blows’) breaking the circuit and preventing damage to the circuit protected by the fuse.