How to Find Insulation R Values
The R value of a material is a measure of that material's effectiveness as an insulator. This property is a common factor in choosing the material with which to construct a home or other building. You can determine the R value of a material experimentally in the laboratory, and it is also typically listed on the packaging of many building materials.
Instructions
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1
Obtain a sample of the test material with known dimensions. The sample will typically have a cubical shape with a standard height, width and thickness. Multiply the height by the width to get the surface area of the sample.
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2
Measure the heat loss through the sample. Heat tends to flow from a hotter area to a colder area. The rate at which the heat transfer occurs for a given sample is dependent upon the temperature. The heat flow rate decreases with the temperature differential and reaches zero when the temperatures of the two areas is equal.
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3
Calculate the R value of the test material. This may be expressed mathematically as R = dT x A/Q where R is the R value, dT is the temperature differential between the two sides of the sample, A is the surface area of the sample and Q is the rate of heat transfer at a temperature differential of dT.
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4
Express the R value in the desired units. You can see from the equation in step three that the R value is expressed in units of temperature -- area/energy. The R value of building materials in the United States is typically measured in degrees Fahrenheit -- square feet/BTUs. The standard unit of measure for an R value is degrees Kelvin -- square meters/watts.
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