A method to calculate transient, steady state temperatures and a few electrical characteristics of meso-size, screen printed, thick film, resistive heaters is presented. Non-linear heat equation for a lumped system of convective-radiative heat transfers is considered. Various important characteristics of heater-sensor assembly are calculated accurately, for constant and varying applied voltages. The parameters determined are average substrate temperature; drive voltage and warm-up time for attaining any specific steady state temperature, electrical characteristics such as temperature dependent heater resistance, current drawn, input electric power etc. For given steady state temperature the method is used to design 'voltage profile', the rate in which applied voltage needs to be increased while powering the heater, to achieve minimum warm-up time eliminating failures by over current. Experimental results are presented that validate the method. A representative case is illustrated where steady state temperature of 650°C is achieved from 25°C in nearly 120 seconds, for a 8.7mm dia. alumina substrate heater, by controlled increase in the applied voltage from 0 to 10.8V always maintaining safe heater current (≤450mA). Also conclusions are drawn on effect of heater size, electrical resistance, and variations in ambient temperature (-40 to 55°C) on warm-up time, peak current, power consumption etc.