Enhancing integrated management of natural resources

A fluid heater has concentrically disposed radiantly heated and convectionally heated sections. The radiantly heated section includes a helically coiled tube defining a cylindrical chamber in which a flame produced by a burner primarily radiantly heats the coiled tube. The helically coiled tube has an outer perimeter about which a plurality of finned tubes are concentrically disposed and are heated by convection transfer of thermal energy. The oil heater embodying the present invention provides a compact oil heater that has greatly increased heating efficiency, reduced heat loss through the shell of the heater, and reduced internal stresses.