We describe the incorporation of interaction between appliance efficiencies and space-conditioning loads into a version of the Oak Ridge National Laboratory (ORNL) computer-simulation model, used by the Northwest Power Planning Council to project residential demand for electricity in the Pacific Northwest. Projections of total demand and estimated impacts of an illustrative appliance efficiency standard are compared with projections generated by the unimproved version of the ORNL model. Projections of total demand by the new model are not greatly different from the projections of the original. However, the new model produces estimates of savings from the illustrative appliance efficiency standard which are substantially less than the original model.