The present invention relates to a heater suitable for heating a flow of natural gas. There is provided a heater (1) suitable for heating a flow of natural gas, comprising a vessel (2) containing a heat transfer fluid, a heat source tube (3) passing through the vessel and being at least partially immersed in the heat transfer fluid, the heat source tube (3) being suppliable with heated gas to allow the heated gas to flow along the heat source tube (3) to evaporate the heat transfer fluid and at least one heat exchanger being connectable to a source of second fluid (9) to be heated, the heat exchanger being arranged so that the second fluid can be heated by the evaporated heat transfer fluid.