The invention relates to a double-pipe heat exchanger for heating liquid heat carriers (e.g. thermal oil or hot water), which consists of a combustion chamber module and a downstream block. All the heating surfaces are formed from double pipes and configured such that they can be effectively cleaned from deposits of rust and ash. All the heating surfaces can be withdrawn from their housing for the purpose of special monitoring or repairs. The double pipes are joined together in circuit terms in such a way that the heat carrier fluid is left only one flow path or a few flow paths (which can be monitored) and controlled. As a result, it is possible to counter the risk of local over-heating of the heat carrier, which - in the case of heat carrier oils - leads to chemical decomposition thereof. Also specified is a circuit for a double-pipe convection heat exchanger which can be used in waste-heat systems (e.g. on the exhaust gas side downstream of internal combustion engines). <IMAGE>
