Households may imperfectly implement energy saving measures. This study identifies two factors resulting in imperfect use of energy-saving technology by households. First, households often continue to use old technologies alongside new ones, and, second, technologies have shorter actual lifetimes than their designed lifetimes. We take these factors into account when computing marginal energy conservation cost and marginal CO2 abatement cost using data collected from a survey of rural households in three provinces in China. The results show that most space heating technologies are cost negative and their marginal abatement cost under full implementation ranges from -60 to 15 USD/t-CO2, while the marginal abatement cost of cooking technologies ranges from 12 to 85 USD/t-CO2. The marginal abatement costs of the majority of technologies increased after accounting for the two implementation factors. The marginal abatement cost in the imperfect implementation scenario is higher, with a range of -1 to 15 USD/t- CO2 for space heating, and 18 to 165 USD/t-CO2 for cooking. Assuming implementation factors are constant until 2035, annually achievable CO2 mitigation by 2035 is estimated to be 57, 11, and 10 Mt-CO2/y in Hebei, Guizhou, and Guangxi Provinces, respectively.