Germany wants one quarter of the energy used to heat homes to come from recycled heat waste generated at industrial plants. The city of Karlsruhe is investing heavily in new infrastructure to make this possible. At the Miro oil refinery in southwest Germany crude oil is turned into products such as petrol, diesel, and gas. The process generates a lot of extra heat, which the plant has to get rid of. \"For distillation you need more than 200 degrees Celsius ... or for cracking processes you need up to 550 degrees and the products must be cooled down to 20 to 40 degrees before they can be stored in the tank,\" Miro\'s General Manager Gerd Löhr said in an interview with DW. Until two years ago, this excess heat was simply pumped into the air. But the city of Karlsruhe noticed this waste and decided it would be better to transfer the heat in pipes towards nearby residences. The process is called district heating and the concept has been around for more than a century. It\'s now being revived in Germany, as the country looks for cleaner, more efficient ways to heat homes and other buildings. The method involves siphoning off residual heat generated in industrial plants and using it to serve the needs of individual customers. \"We can see, we have two main pipelines feeding into the city,\" Energy Consultant Holger Ochs from Karlsruhe Council told DW, pointing to maps of the area. \"There is the Miro oil refinery, and here is a pipeline from (energy provider) EnBW. It\'s a coal-fired power plant. When you burn coal, only 40 percent of the energy can actually be used to make electricity. Fifty percent of the energy is heat. And you can\'t do anything with this heat in the power station. But you can use the heat elsewhere. So we buy it off them and transfer it to the city,\" Ochs explained. Many advantages, but high costs It will cost 30 million euros to expand Karlsruhe\'s district system. This will make it possible for the local city council to add some 30,000 houses to the system, which will save an estimated 65,000 tons of carbon dioxide, a greenhouse gas responsible for global warming. \"In Germany, so much heat is generated by electricity production alone that we could heat the entire country. And we just throw this heat away,\" said Ochs. \"So district heating is about using heat that already exists. It is already produced at the power station and at the oil refinery. So from an ecological point of view it means the heat doesn\'t have to be generated again in the individual houses.\" District heating has many advantages. Not only is it environmentally friendly and relatively cheap for customers, it also frees people from the need to have their own boilers, storage tanks and chimneys. There are no extra costs like having a chimney sweep and getting a plumber in to fix your boiler. But this method has one major disadvantage, however. It costs a lot of money to lay the pipelines and install the heat exchangers to allow the heat to get into homes, businesses and public buildings. \"Here you see how they build the pipelines in Karlsruhe,\" Engineer Sasha Englert from Karlsruhe Council said, pointing down to a deep trench in the road where the new district heating pipes are being laid. \"There are the welders, they need for to five hours for every pipe, after they have done this work, the next pipeline will go on.\" Karlsruhe council is paying 1,000 euros a meter for the pipeline. To expand the current system by one kilometer will cost them one million euros. \"It is so expensive because it is very deep. We have a lot of earth to dig away. We need special sand around it so it won\'t corrode. This is very expensive,\" Englert said. District heating in Germany has a market share of just 14 percent, which is low compared to many other northern European countries with high heating needs. But just last week Germany amended its law regulating the use of heat from power stations and other industrial complexes. The legislation increases the subsidies available for district heating projects by up to 30 percent.