Thermal Resistance Converter

About Thermal Resistance

Thermal resistance is a measure of a material or system's ability to resist heat flow. It is the reciprocal of thermal conductance and is fundamental to understanding heat transfer processes in engineering, building science, and thermal management.

Understanding Thermal Resistance Units

Thermal resistance can be expressed in several different units depending on the application and region:

• Kelvin per watt (K/W): The base SI unit for thermal resistance, measuring the temperature difference (in Kelvin) produced across a material by a heat flow of one watt
• Celsius degree per watt (°C/W): Equivalent to K/W since the Celsius and Kelvin scales have the same interval size
• Fahrenheit degree per watt (°F/W): Common in U.S. applications, where temperature differences are expressed in Fahrenheit
• R-value (m²·K/W): The thermal resistance per unit area, used to compare insulation materials independent of their thickness
• R-value IP (ft²·°F·h/BTU): The imperial version of R-value commonly used in the U.S. building industry
• Tog: A unit used mainly for insulation properties of textiles and bedding (1 tog = 0.1 m²·K/W)
• Clo: A unit used for clothing insulation (1 clo = 0.155 m²·K/W)

Common Thermal Resistance Conversions

• 1 K/W = 1 °C/W
• 1 K/W = 1.8 °F/W
• 1 K/W = 3.412 K/BTU/h
• 1 R-value (m²·K/W) = 5.678 R-value IP (ft²·°F·h/BTU)
• 1 tog = 0.1 m²·K/W
• 1 clo = 0.155 m²·K/W

Applications of Thermal Resistance

Thermal resistance concepts are applied in various fields and applications:

• Building insulation: R-values are used to rate and compare insulation materials for walls, roofs, and windows
• Electronics cooling: Thermal resistance in K/W helps design heat sinks and thermal management solutions for electronic components
• Clothing and textile design: Tog and clo values guide the development of appropriate clothing for different climates
• HVAC systems: Thermal resistance calculations determine heat transfer rates in heating and cooling systems
• Food packaging: Thermal resistance properties affect how well food containers maintain temperature
• Cryogenic systems: Managing thermal resistance is critical in ultra-low temperature applications
• Spacecraft design: Thermal resistance management is vital for temperature control in space environments

Thermal Resistance in Buildings

In building science, higher R-values indicate better insulation performance. Typical R-values (in m²·K/W) for common building materials include:

Thermal Resistance in Electronics

In electronics, thermal resistance is often represented as a network of resistances describing heat flow paths. Typical thermal resistance values include:

• CPU to heat sink interface: 0.1 - 0.5 K/W
• Small passive heat sink: 4 - 15 K/W
• Large active heat sink (with fan): 0.2 - 1.0 K/W
• Thermal interface material (TIM): 0.2 - 1.5 K/W
• Junction-to-case for high-power LEDs: 5 - 15 K/W

Calculating Total Thermal Resistance

For systems with multiple components in series, the total thermal resistance is the sum of individual resistances:

R_total = R₁ + R₂ + R₃ + ... + R_n

For components in parallel, the calculation follows the same pattern as parallel electrical resistances:

1/R_total = 1/R₁ + 1/R₂ + 1/R₃ + ... + 1/R_n

Relationship to Other Thermal Properties

Thermal resistance (R) relates to other thermal properties as follows:

• R = 1/G, where G is the thermal conductance
• R = L/(k·A), where L is thickness, k is thermal conductivity, and A is cross-sectional area
• R = 1/(h·A), where h is the heat transfer coefficient and A is surface area
• R-value = R·A, where A is the area of heat transfer

Our thermal resistance converter provides accurate conversions between all these units, making it easy to translate between different measurement systems for engineering calculations, building design, and thermal management applications.