Higher heating value in the context of "Barrel of oil equivalent"

Autogas is liquefied petroleum gas (LPG) used as a fuel in internal combustion engines of vehicles as well as in stationary applications such as generators. It is a mixture of propane and butane.

Autogas is widely used as a "green" fuel, as its use reduces CO₂ exhaust emissions by around 15% compared to petrol. One litre of petrol produces 2.3 kg of CO₂ when burnt, whereas the equivalent amount of autogas (1.33 litres due to the lower density of autogas) produces 2 kg of CO₂ when burnt. CO emissions are 30% lower compared to petrol, and NO_x is reduced by 50%. It has an octane rating (MON/RON) that is between 90 and 110 and an energy content (higher heating value—HHV) that is between 25.5 megajoules per litre (for pure propane) and 28.7 megajoules per litre (for pure butane) depending upon the actual fuel composition.

Condensing boilers are water heaters typically used for heating systems that are fueled by gas or oil. When operated in the correct circumstances, a heating system can achieve high efficiency (greater than 90% on the higher heating value) by condensing water vapour found in the exhaust gases in a heat exchanger to preheat the circulating water. This recovers the latent heat of vaporisation, which would otherwise have been wasted. The condensate is sent to a drain. In many countries, the use of condensing boilers is compulsory or encouraged with financial incentives.

For the condensation process to work properly, the return temperature of the circulating water must be around 55 °C (131 °F) or below, so condensing boilers are often run at lower temperatures, around 70 °C (158 °F) or below, which can require larger pipes and radiators than non-condensing boilers. Nevertheless, even partial condensing is more efficient than a conventional non-condensing boiler.