SHIJIAZHUANG - For those already choking on air in north China, the central heating season could mean more wheezy days in the coming months.

With this in mind, Shijiazhuang -- one of the most polluted cities -- is trying to to cut pollutants released by heating.

About 300 kilometers southwest of Beijing, Shijiazhuang is capital of Hebei Province. Hebei claimed seven of the 10 most polluted cities in the country in the third quarter of the year.

Apart from converting coal-fired boilers to gas, Shijiazhuang has piloted utilizing  "spare" heat in industrial waste water to warm a community covering 100,000 square meters.

The program in Lijingwan uses effluent from a refinery to warm clean water before the clean water is heated again by efficient electric boilers in basements. The combination of hot industrial waste water and efficient  boilers can cut energy consumption by 44 percent, the local heating office said.

For the Lijingwan neighborhood alone, that means 868 tonnes of coal could be saved in a single winter.

"We used coal boilers before, but they were not hot enough, so we had to buy electric radiators," said Xie Yanru, a resident of Lijingwan. "Now the new system keeps the rooms warm and at stable temperature, and we don't need to pay extra fees."

The heating office in Shijiazhuang is optimistic. Industrial waste heat could help warm an area of 50 million square meters five years from now.

"It turns the waste into a gold mine," said Zhang Ye, vice mayor of Shijiazhuang, "and reduces emissions."

Gree Electric Appliances, who provided the equipment for the program, claim that some 275,000 tonnes of coal can be saved a year for every 10 million square meters of floor area, if coal boilers are replaced. The new method also substantially cuts emissions of carbon dioxide, sulfur dioxide, and dust.

The scheme is especially significant and feasible in northern Chinese cities like Shijiazhuang, which need to fight the smog and have mature industrial bases or sewage treatment systems that can provide the residual heat, said Zhang. Waste heat generated by local power and chemical plants is enough for a floor area of 200 million square meters.

Earlier this month, the heating office of Jinan, capital of eastern Shandong province, announced its own similar pilot program. The Drainage Group of Beijing has a similar program in the Olympic Village.