A control strategy selectively controls the heating of fluid lines equipped with line heaters that may be utilized with a selective catalytic reduction system. The control strategy measures a tank temperature representative of reductant agent in a storage tank and a representative ambient temperature representative of an ambient temperature proximate the fluid line. The control strategy determines a lowest possible reductant agent temperature (“LPRAT”) based on the measured tank temperature and representative ambient temperature. The LPRAT is compared with a desired reductant agent temperature and, in response to the comparison, the control strategy may activate the line heater.