I'd be surprised if it is true. The problem with green wood is the water that must be boiled away before the wood can burn. There is a tremendous amount of energy consummed to turn 212 degree water into 212 degree water vapor, near 500 times the energy to raise the temperature of water from 211 degrees to 212 degrees. So first you have to raise the water temperature to 212 degrees, then boil it, then heat it some more, and the net energy going into the water alone can be larger than the energy available from the combustion. That's why green wood sometimes just goes out. Unless you can cool the flue gas temperature below 212 degrees, that energy is lost out the chimney. Most woodstoves are going to have flue gas temperatures well over 300 degrees, more like 500. Even if you could cool the flue gases to under 212, you would have a big mess. Water soaked creosote running down your flue, yuck! IMHO, burning green wood wastes a lot of energy, which translates into cutting more wood.