It adds q0 to the total flux across the selected boundaries. Enter a value for 
q0 to represent a heat flux that enters the domain. For example, any electric heater is well represented by this condition, and its geometry can be omitted. 
 
    Enter a value for the Heat transfer coefficient h and an 
External temperature, 
Text. The value depends on the geometry and the ambient flow conditions. Convective heat flux is defined by 
q0 = h(Text − T).
 
    For Heat rate enter the heat rate 
P0 across the boundaries where the 
Heat Flux node is active. In this case 
q0 = P0 ⁄ A, where 
A is the total area of the selected boundaries.
 
    The settings are the same as for the Heat Source node and are described under 
Frame Selection.