Micro combined heat and power or micro-CHP is an extension of the idea of cogeneration to the single/multi family home or small office building in the range of up to 50 kW. Local generation has a higher efficiency as it lacks the 8-10 % energy losses when transporting electricity over long distances and the 10–15 % energy losses on heat transfer in district heating networks due to the difference between the thermal energy carrier (hot water) and the colder external environment. The most common systems use natural gas as their primary energy source and emit carbon dioxide.