The 39E Reko boiler fitted to the engines is a combustion chamber boiler and can generate 15 tons of steam per hour, thanks to the improved ratio of radiative to tube heating area. This is considerably higher than, for example, the new DB boiler which generates only 13.3 tons of steam per hour. Fitted with this boiler, the engine was able to exceed the performance requirements that it originally had for the 20 bar boilers, in spite of its small cylinders.
