In commercial thermal wood modification processes nitrogen, steam or oil has been used for the reduction of oxygen content in the reactor atmosphere. In present study no special heating medium, but an initial vacuuming step has been used for this purpose. Mass loss, resistance to fungal decay, dimensional stability, bending strength and modulus of elasticity of heat treated wood were evaluated and compared to the results of known processes. At firm process duration, treatments at maximum temperatures between 190 °C and 210 °C gave products with optimal properties. Considerably improved resistance against Gloeophyllum trabeum and Coniophora puteana and dimensional stabilisation up to 48 % were observed at maximum 20 % and 53 % reduction of modulus of elasticity and rupture respectively. Without use of any heating medium, initial vacuuming step alone ensure appropriate conditions for competitive product quality.

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