What unit is used to express thermal transmittance (U-factor)?

The unit used to express thermal transmittance, commonly referred to as the U-factor, can be represented in different systems of measurement.

In the metric system, it is expressed as W/m²K, where "W" denotes watts, "m²" indicates square meters, and "K" represents the temperature difference in kelvins. This unit is used to quantify the rate of heat transfer through a structure, indicating how effective the building element is as an insulator.

In the imperial system, the U-factor can also be represented as Btu/hr/ft²R, where "Btu" stands for British thermal unit, "hr" is hours, "ft²" signifies square feet, and "R" represents the temperature difference in Rankine. This unit serves a similar purpose, giving insights into how much heat is lost or gained through a building component over time.

Both units effectively measure thermal transmittance, demonstrating how heat is conducted through materials. Therefore, stating that both units represent the U-factor is correct and underscores the versatility of this measurement across different measurement systems.