The degree days are the days that are based on the assumption of the outside temperature which is 65°F, thus we don't need to have the heating or the cooling to get comfortable.
For the (C.D.D) day the ( 40° + 32° ) / 2 = 32 which is ( 36-32 ) will be 4° F
and for the ( H.D.D ) day will be ( 65°- 36° ) F will be 29° F.
