The present invention offers an improved axial heat exchanger for exchanging heat between a gas medium and a fluid or liquid medium. The axial heat exchanger comprises a longitudinal and substantially axially extended outer channel that is adapted to enclose a flow of a first gas medium. The heat exchanger also comprises a plurality of substantially parallel inner channels that are adapted to enclose a flow of a second liquid medium. The inner channels are arranged inside the outer channel so as to extend substantially axially along the inside of said outer channel for enabling a transfer of heat between said first gas medium and said second liquid medium. The heat transfer is improved to some extent as the number of inner channels increases and it is further improved in that at least one of the inner channels is joined with at least one elongated sheet. The sheet is arranged to extend substantially axially along the inner channel so as to substantially coincide with the direction of flow of the first gas medium through the outer channel.