How is the overall coefficient of heat transmission expressed?

The overall coefficient of heat transmission, often referred to as the overall heat transfer coefficient, is typically expressed in BTU per square foot per degree Fahrenheit. This measurement quantifies the rate of heat transfer through a material or assembly of materials based on the temperature difference across it. It is a crucial parameter in understanding how effectively a material insulates against heat loss or gain.

The unit BTU per square foot per degree F specifically indicates how many BTUs of heat will pass through one square foot of a material for every degree Fahrenheit of temperature difference across the material. This helps engineers and architects evaluate the thermal performance of building materials and assemblies, guiding them in designing energy-efficient structures.

The other options provide unit measures that do not directly correspond to the overall coefficient of heat transmission. Watts per square foot measures power, square feet per hour is a rate of area, and kilowatts per hour is a measure of energy usage over time, but none reflect the specific thermal transmission characteristics needed to assess heat transfer in buildings and materials.