The time rate of steady-state heat flow through a unit area of a material or construction induced by a unit temperature difference between the body surfaces. In English (inch x pound) units of measurement, the number of British thermal units (Btu) that pass through a specified thickness of a 1-square-foot sample of material in one hour with a temperature difference between the two surfaces of 1 degree Fahrenheit.
In English (inch x pound) units, it is expressed as Btu/h x ft2 x F.
Note 1: A thermal conductance (C) value applies to a specific thickness of a specific material.
Note 2: It is mathematically incorrect to multiply or divide the thermal conductance (C) value for a specific thickness of a material to determine the thermal conductance value of a different thickness of the same material.
Note 3: It is mathematically incorrect to add thermal conductance (C) values to determine overall thermal performance. If it is necessary to determine the overall thermal performance of a construction, it is appropriate to convert the individual thermal conductance (C) values to thermal resistance (R) values i.e. R = 1/C and then add the thermal resistance values i.e. RtÊ= R1 + R2 +« Back to Glossary