Ultimate Analysis
A procedure for determining the primary elements in a substance (carbon, hydrogen, oxygen, nitrogen, sulfur, and ash).


Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.

Unglazed Solar Collector

A solar thermal collector that has an absorber that does not have a glazed covering. Solar swimming pool heater systems usually use unglazed collectors because they circulate relatively large volumes of water through the collector and capture nearly 80 percent of the solar energy available.

Underground Home

A house built into the ground or slope of a hill, or which has most or all exterior surfaces covered with earth.

Unitary Air Conditioner

An air conditioner consisting of one or more assemblies that move, clean, cool, and dehumidify air.

Unvented Heater

A combustion heating appliance that vents the combustion by-products directly into the heated space. The latest models have oxygen-sensors that shut off the unit when the oxygen level in the room falls below a safe level.

Useful Heat

Heat stored above room temperature (in a solar heating system).


A regulated entity which exhibits the characteristics of a natural monopoly (also referred to as a power provider). 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.

U-Value (see Coefficient of Heat Transmission)

The reciprocal of R-Value. The lower the number, the greater the heat transfer resistance (insulating) characteristics of the material.