for coal and oil, the NCV is about 5 % less than the GCV. for most natural and manufactured gas, the NCV is about 10 % less . Where fuel characteristics (moisture, hydrogen and oxygen contents) are known, the 2006 IPCC Guidelines give a more precise method to convert GCV to NCV data: NCV = GCV − 0.212H − 0.0245M − 0.008Y. M – Moisture, H