Heating Month Threshold HDD/month is used to identify the bills that do not have significant heating usage and are candidates for base load estimation. The heating threshold is used for all analysis periods. TREAT uses the reference temperature and average daily temperatures to calculate heating degree-days in each utility bill. It compares the HDD value to the entered winter bill threshold. If the difference for a 30-day bill is less then the threshold, the bill is assumed to be a non-heating bill. This algorithm is applied to all the bills that have base and/or cooling load in addition to the heating load. Heating threshold depends on the building heat loss rate, reference temperature, and specifics of heating system control. For example, you anticipate that the building has the heat loss rate (slope) of 15Btu/ SF-HDD and you set your Heating Month Threshold to 50 HDD/month. Then all the months during which the heating energy usage was less than 15 × 50= 750Btu/ SF-month will be used