A degree day is defined by the average temperature being below which reference temperature?

The concept of a degree day is used primarily in heating and cooling calculations for buildings and is crucial for understanding energy consumption requirements. It is based on the idea of measuring how much the temperature deviates from a set reference point over a period. In this case, the reference temperature commonly used for heating degree days is 65 degrees Fahrenheit.

When the average daily temperature falls below this threshold, degree days are counted, with each degree below 65 representing a degree day. This measurement helps in estimating how much heating is required to maintain comfortable indoor temperatures, allowing builders and HVAC professionals to design systems that are efficient and adequately sized.

Choosing a reference temperature of 65 degrees Fahrenheit makes intuitive sense in the context of comfort and the typical heating requirements for buildings, thus reinforcing why this answer is the most applicable in this scenario.