Design Temperature Difference

The design temperature difference is the variation in degrees Fahrenheit between the outside and inside design temperatures. It is used in the heat transmission loss formula (see below) and is a cru­cial factor in heating calculations.

Be careful that you obtain the degree difference between the two temperatures; do not simply subtract the smaller figure from the larger one. For example, if the outside and inside design tempera­tures are —20 and 70°F, respectively, the design temperature differ­ence will be 90° (20° below zero plus 70° above zero).

Posted in Audel HVAC Fundamentals Volume 1 Heating Systems, Furnaces, and Boilers