Abstract: An apparatus and a method of assembling a panel heater for use in a corrosive environment includes a planar heating element, a planar non-conductive carrier for supporting a conductive ground plane thereon, a planar heat sink supporting the heating element, and a fluoropolymer envelope enclosing the heating element, the carrier, the ground plane and the heat sink to protect same from corrosive environments. The heat sink and carrier have a coefficient of expansion which is substantially equal to minimize the effects of unequal expansion and contraction of the heater.