The requirements for the quality of steel products dictate the need to increase the share of evacuated steel. In addition, the growing cost of fuel, as well as the desire of society and the state to decarbonize various industries, including ferrous metallurgy, requires companies to reduce fuel costs and switch to more modern and cleaner technologies. Reducing the specific fuel consumption, and, accordingly, emissions, is possible due to the transition to continuous production, minimizing the cost of heating the equipment and maintaining the set temperature in the degasser during technological downtime. The article deals with the issues of steel melt degassing in U-type continuous degassers in continuous steel making units. Aim. To consider the influence of rarefaction of a gas bubble on the characteristic size over the melt, speed and time of its surfacing in a U-type degassing unit. Based on the obtained dependences, to determine the characteristic size of a vacuum chamber and energy effect of switching to a continuous vacuumization. Methods.. Results. The authors have determined a bubble characteristic size in a steel melt under vacuum of different degrees. They studied the effect of vacuum on vacuumization speed and the degassing unit dimensions. The energy effect of switching to continuous vacuumization was determined. The proposed methodology is valid for liquid media, the calculations are presented on the example of molten steel. Based on the conducted calculations, the depression influence on molten steel vacuumization was determined. The vacuum chamber dimensions, comparable with RH-vacuum cleaners presented at the market of similar productivity and quality of finished products, as well as reducing energy consumption for steel degassing in a continuous vacuum degasser, compared with the existing circulating installation, were determined.