This article describes a household production model in which energy-efficient durable goods cost less to operate so households may use them more. The model is estimated using household-level data from a field trial in which participants received high-efficiency clothes washers free of charge. The estimation strategy exploits this quasi-random replacement of washers to derive precise estimates of the household production technology and a demand function for clothes washing. During the field trial, households increased clothes washing on average by 5.6% after receiving a high-efficiency washer, implying a price elasticity of −.06. The complete model is used to evaluate the cost-effectiveness of recent changes in minimum efficiency standards for clothes washers.