What term describes the coefficient of heat transmission in BTU, per area, per thickness, per temperature delta per time?

The term that accurately describes the coefficient of heat transmission in BTU, per area, per thickness, per temperature delta per time is known as the K Factor.

K Factor specifically addresses the measure of thermal conductivity of a material, indicating how well it conducts heat. It is expressed in units of BTU per hour, per square foot, per degree Fahrenheit (or Celsius) per inch of thickness. This factor is critical in understanding how insulation materials will perform in terms of heat loss or gain, allowing for better energy efficiency designs.

In comparison, the U-Value represents the overall heat transfer coefficient of a building assembly, factoring in multiple materials and their thicknesses; this would not be the appropriate term for the coefficient of just one material's thermal transmission. Thermal conductivity refers to the ability of a material to conduct heat, but it is considered a broader term that can overlap with K Factor in certain contexts. The Heat Factor is not a standard term used in this context, making K Factor the best choice to represent this concept accurately.