A heat exchanger includes a body 4 on the surface of which are provided helical or spiral paths 5 which will provide multiple and turbulent flow paths A for a first fluid such as water which is caused to flow through chamber 3 relative to a spirally wound heat exchange tube 6 and in a heat transfer relationship with a second fluid flowing through the tube 6. The tube 6 has one or more further helical or spiral flow paths 9 on its external surface. The multiple flow paths A will extend the residence time for the first fluid within the heat exchanger 1 and this together with the turbulence will maximise heat transfer. Preferably a portion of the first fluid flow will be through a central aperture in body 4 where turbulence is also created by the helical or spiral paths of the tube 6 as it extends through the aperture.