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UA: A measure of the amount of heat that would be transferred through a given surface or enclosure (such as a building envelope) with a one degree Fahrenheit temperature difference between the two sides. The UA is calculated by multiplying the U–Value by the area of the surface (or surfaces).

U-value or U-factor: A measure of how well heat is transferred by the entire window –– the frame, sash and glass –– either into or out of the building. U–value is the opposite of R–value. The lower the U–factor number, the better the window will keep heat inside a home on a cold day.

Ultrahigh Voltage Transmission: Transporting electricity over bulk–power lines at voltages greater than 800 kilovolts.

Unbundling: Disaggregating electric utility service into its basic components and offering each component separately for sale with separate rates for each component. For example, generation, transmission and distribution could be unbundled and offered as discrete services.

Unconditioned Space: A space that is neither directly nor indirectly conditioned space, which can be isolated from conditioned space by partitions and/or closeable doors.

Unfinished Oils: All oils requiring further processing, except those requiring only mechanical blending. In most cases, these are produced by partial refining or are purchased in an unfinished state for conversion to finished products by further refining.

Unfractionated Streams: Mixtures of unsegregated natural gas liquid components, excluding those in plant condensate. This product is extracted from natural gas.

Universal Service: Electric service sufficient for basic needs (an evolving bundle of basic services) available to virtually all members of the population regardless of income.

Unleaded Gasoline: Gasoline that has had tetraethyl lead removed in conformance with federal and state regulations. It does not contain more than 0.05 gram of lead per gallon and no more than 0.005 gram of phosphorus per gallon. Premium regular and midgrades are included, depending on the octane rating.

Upgrade (Electric Utility): Replacement or addition of electrical equipment resulting in increased generation or transmission capability.

Uprate (Electric Utility): An increase in the rating or stated measure of generation or transfer capability.

Uranium: A radioactive element, found in ores, of which atoms can be split to create energy.

Uranium Enrichment: The process of increasing the percentage of pure uranium above the levels found in naturally occurring uranium ore, so that it may be used as fuel.

Utility: A regulated entity which exhibits the characteristics of a natural monopoly. For the purposes of electric industry restructuring, "utility" refers to the regulated, vertically–integrated electric company. "Transmission utility" refers to the regulated owner/operator of the transmission system only. "Distribution utility" refers to the regulated owner/operator of the distribution system which serves retail customers.