| Term | Definition |
|---|
| UL Listed | Product certification that indicates the product meets safety standards determined by Underwriters Laboratories. (ULC and cUL indicate Canadian requirements.)
|
| Ultimate Analysis | See "Analysis Ultimate."
|
| Unaccounted-For Loss | That portion of a boiler heat balance which represents the difference between 100 per cent and the sum of the heat absorbed by the unit and all the classified losses expressed as per cent.
|
| Unburned Combustible | The combustible portion of the fuel which is not completely oxidized.
|
| Unfired Pressure Vessel | A vessel designed to withstand internal
pressure, neither subjected to heat from products of combustion nor an integral part of a fired pressure vessel system.
|
| Use Factor | The ratio of hours in operation to the total hours in that period.
|
