Energy Use Investigation 8.2:

Compute the R-Value of a Material

  1. Find the temperature difference T on the two sides of the material
  2. Multiply it by the area A of the material
  3. Divide it by the rate of heat flow H through the material.

R-Value = T x A / H


Question 8.3
What is the R-value of a 2-square-foot window that allows 20 btu of heat to flow through it per hour?
The indoor temperature is 65°F and the outside temperature is 55°F.


Celsius (°C) to Fahrenheit (°F)*:

Use this formula to convert °C to °F:
°F = (°C x 9/5) = 32
We use non-metric temperature (°F) in our calculations because most American energy-related industries have not converted to the metric system. To use °C would add an extra step of complexity to figure out the R-value of insulation, which use btus and °F.

* See explanation of temperature scales.