Cooking with dirty fuel is known to be one of the biggest sources of indoor air pollution in developing countries. I estimate the health impact of indoor air pollution using a nationwide fuel-switching program, the largest household energy transition project ever attempted in the developing world, affecting more than 50 million homes in Indonesia. This program focused on replacing a dirty cooking fuel, kerosene, with cleaner cooking fuel, liquid petroleum gas (LPG). I use a difference-in-differences design with time-varying program intensities to capture the dynamic increase in the households’ access to LPG. A 10-percentage-point increase in the program intensity –measured by the number of free initial LPG packages distributed –reduces infant mortality rate by 3.3 percentage points, or 1.2 infants per 1,000 live births annually. This study highlights the fact that adopting cleaner energy can have a substantial health impact beyond what is currently known.