extremely low temperature of the chips in cold seasons the chips that lie above the fluid level established by the impregnation fluid can be heated by the addition to the impregnation vessel of external steam such that a temperature of the chips of at least 20 degrees c and up to 80 degrees c at the most is obtained on the chips before the chips reach the fluid level that has been established by the impregnation fluid a maximum liquid level liq_lev is established in the vessel under the chip level ch_lev in the vessel control of the level occurs by adjusting the balance between the addition of liquids to the vessel and withdrawal of liquids from the vessel by any appropriate control system the liquid level must thus be established such that it lies under the chip level ch_lev in the vessel the second level of liquid liq lev in the vessel establish a total liquid volume z 1 amp z 2 in the vessel the level ch_lev of the chips above the level liq_lev of the liquid i e the distance marked h 0 in figure is preferably at least 2 meters and more preferably at least 5 meters when impregnating eucalyptus in the case of wood raw material of lower density for example softwood which has a density that is up to 30 lower a corresponding increase.