We use a difference in difference model to examine the impact of central winter heating on air pollution in China. The estimation includes how does the winter heating affect (i) air quality, and (ii) hazard level of pollutants. Our data are daily Air Quality Index (AQI) records in mid-November when the heat is turned on and mid-March when heat is turned off in over 150 cities. Both Ordinary Least Square (OLS) and Ordered Logit model show that winter heating contributes significantly to air pollution, especially in the period when central heating is switched on. The central heating causes 51.3% higher AQI, and the air is 13% more likely to be hazardous to the sensitive group (hazard level=3). Northern cities are more polluted than southern ones. It is also found that air quality in cities with higher GDP per capita is better; population, number of cars and electricity used by industry also contribute to air pollution.