A steam reformer, comprising a combustion chamber, catalyst tubes arranged in several rows, feed conduits for the educt gas, which extend below the bottom of the combustion chamber, burners for heating the catalyst tubes which are installed in the bottom of the combustion chamber and are directed vertically upwards into the combustion chamber, feed conduits extending below the bottom of the combustion chamber, each for supplying the air and the fuel gas to the burners, openings installed in the ceiling of the combustion chamber for discharging the burner waste gas, and channels extending above the ceiling of the combustion chamber for discharging the burner waste gas.