Which is better value for money - Air dried @25% MC or Kiln dried Firewood @ 20%MC ? in Firewood forum Posted 15 hours ago · Report reply On 26/05/2020 at 12:47, aesmith said: Assuming you get 5kWh per kg of dry wood, the direct loss due to water is only around 3.3% for wood at 20% m/c, or just over 4% for 25. I used 5.17kWh/kg for dry wood and my calculation gave 4.29% loss in steam at 300C.for 20% and 5.36% at 25%. I would like to know if people using flue temperature gauges actually see temperatures as high as 300C as it seems a bit high to me. Flue temperatures have to be above 100C at the chimney exit to avoid condensation with wetter wood but it would take a bit of working out what the dew point would be for dry wood, it would be less than 100 because the partial pressure of the water vapour would remain above the partial pressures of all the other combustion gases down somewhere below 100C. Of cause the chimney would be absorbing some heat and depressing the temperature of the column of flue gases, more so if it is not insulated. I use this as a feature, so the chimneybreast's thermal mass keeps the house warm after the fire is out.