Heat Transfer Tool Guide


What this tool does – [Tool]

This tool is most often used to find heat transfer through a surface, but because it is a solve-all tool, you may solve for any one of the five values.

Calculated values

  • Heat transfer; or
  • Temperature difference; or
  • R-value; or
  • Time interval; or
  • Area.


  • Clicking the label for any input or result will cause a popup help box to appear. This help box includes the allowed and normal values (for inputs).
  • Because this is a solve-all tool, you may find a result for any one of the five values. Click the radio button to the left of the value label to solve for that value. When you check a radio button to solve for a value, the color of the label changes from black to blue.
  • This tool is most often used to solve for “Heat transfer”, the last of the five values.
  • With this tool you can calculate annual heat loss/gain through a surface by entering “1 day” for the time and then entering the number of heating degree days for the temperature difference. You will receive a warning message indicating that your temperature difference input is outside the normal range, but you may proceed with the calculation.


It is probably easiest to think of heat transfer through a three-dimensional object, like a house window, as being characterized by conduction only. However, heat transfer through building parts is usually a combination of conduction, convection, and radiation. The part that each of these plays is represented by the rated R-value of the building part, for example, the complex heat transfer through fiberglass insulation is represented by an R-value of 3.2 per inch (RSI of 0.564).

This RED Calc tool is based on one of the two basic equations used for sizing heating and cooling systems for dwellings. The other equation calculates hourly heat loss or gain attributed to air leakage.