A simple model for monitoring natural gas consumption in large aggregates of houses is developed by extending the individual-house scorekeeping approach. The model is tested on aggregate utility billing data for gas-heated houses in New Jersey. The resulting aggregate Normalized Annual Consumption (NAC) index is extremely well determined, and the corresponding R**2 values of the fits of the data are very high. The individual PRISM parameters, though more erratic than the NAC index, suggest interesting structure in the year-to-year consumption changes.