China Petrochemical Corp, or Sinopec, the world's largest refiner by volume and the country's biggest geothermal developer, vows to further tap geothermal energy sources as part of the widespread adoption of renewable energy nationwide.

The geothermal heating service of the oil giant will provide emissions-free heating for residential areas, adding up to nearly 85 million square meters this winter, covering millions of households in more than 60 cities and counties in Tianjin and in Shaanxi, Hebei, Henan, Shandong, Shanxi and Hubei provinces.

The company's more than 700 geothermal heating stations are expected to reduce about 4.2 million metric tons of carbon dioxide emissions annually, it said.

Geothermal energy — heat emanating from the Earth — is considered sustainable and clean. The heat can be harnessed from natural hot water sources, underground rock heated by the Earth and molten rock called magma.

Geothermal energy is not unusual in China — the Tibet autonomous region and Yunnan and Sichuan provinces are considered some of the best source regions. The country plans to boost geothermal energy generation in those areas.

Sinopec expects to boost its geothermal capacity to heat 120 million cubic meters of space by 2023 and significantly reduce coal consumption with geothermal energy in 20 cities nationwide next year.

China has stepped up its efforts to develop geothermal energy in recent years, said Luo Zuoxian, head of intelligence and research at the Sinopec Economics and Development Research Institute.

The nation is doing this because geothermal heating is by far the most economical means of heating available and also an answer for China's carbon neutrality goals, he said.

To better help with community integration, Sinopec provides a customer service hotline to answer questions. It has also established customer service centers in Hebei, Henan, Shandong, Shaanxi and Shanxi provinces and other places, it said.

China considers geothermal energy as a key heating source and has been actively working on detailed measures to further utilize this clean energy. Recent figures show that the installed capacity for geothermal energy that can be used directly in China has reached 40.6 gigawatts, 38 percent of the world's total.

"With its commitment to utilize geothermal energy in its effort to make cities free of air pollution, China has encouraged incredible growth in geothermal heating capacity," said Alexander Richter, president of the International Geothermal Association.

Sinopec Green Energy Geothermal Development Co Ltd, the geothermal heating arm of Sinopec, has formed a joint venture with Icelandic partner Arctic Green Energy, and it vows to grow its business by 25 percent annually for the next few years, given the increasing demand for clean heating.