Raw sewage being used to heat and cool buildings in Colorado, Denver, USA. This renewable heating system utilises the ambient temperature of wastewater (12-15 degrees Celsius) to heat and cool clean water. In an exchange chamber, sewage pipes run alongside clean water pipes. During the winter, water in the clean water pipes is heated by the ambient wastewater temperature. During the summer, water in the clean water pipes is cooled by the ambient wastewater temperature.