The VAKAVLAS type heat exchanger is made up of a sheet-metal frame, bundle of tubes made of U-tubes, distribution and collecting chambers with inlet and outlet nozzles. U-tubes can be smooth or ribbed with rolled-on aluminium profile. The heat exchanger can be designed with a horizontal or vertical direction of gas media flow. The bundle of tubes can be made as removable from the frame or firmly welded to the frame. The reducing inlet and outlet parts can be made with removable or rigid connections to the sheet-metal frame. It is used eg. as a flue gas heat exchanger heating liquids, or as a flue gas / air recuperator.