A model is given for blast waves which are dominated by heat transfer rather than by shock heating and adiabatic expansion. The wave motion is attributed to a net heat flowW(watts/cm2) from the expanding hot core to the surrounding cold gas (density &rgr;1). The surface of the hot core is initially a supersonic heat wave without a shock. It changes into a subsonic heat wave with a leading shock after quickly passing through the detonation mode. A quantitative analysis of the space time trace near the detonation point yields the enthalpyhfand other parameters of the hot core, the thermal response functionhf=f(W) of the background medium, and the blast wave energyE0=const &rgr;1V2sr3H(whereVsis the shock front velocity andrHis the radius of the hot core). The analysis shows the steady transition of such a blast wave from the early stage of a ’’thermal’’ wave with negligible mass motion to the late stage (which approaches ’’classical’’ blast waves) with negligible heat transfer. Applications to laser spark plasmas are discussed.