The present disclosure relates to a heating system for an exhaust gas treatment system. The heating system comprises a first heating element comprising a receiving surface for receiving a reductant fluid and a second heating element, which may surround the first heating element. The second heating element may be a thermochemincal or thermophysical device. In a first mode of operation the second heating element is arranged to receive thermal energy from engine exhaust gas. In second mode of operation the second heating element transfers thermal energy to heat the first heating element.