Calculations for heat tracing must first start with an estimate of heat losses from the piping to be insulated and traced. The primary resistance for insulated pipe should be the conduction through the insulation and this should be the starting point for the calculations. From this heat loss calculation, the total quantity of petrotherm (or any other heating medium) required per unit length of piping can be determined such that the heat loss is balanced by heat supplied by the tracing. Flow rate, pressure drop and temperature loss of the tracing medium must be checked to determine maximum tracing length per circuit.