An electric heater assemblage for attachment to the air intake opening of a fuel vapor recovery canister of the type containing material adapted to alternately adsorb and store, or release fuel vapor. The assemblage includes a wafer of electric resistance heating material, and electrical connections for effecting energization of the wafer. The wafer has opposite expansive surfaces, and there is a first wall located at one side of the wafer and having an expansive surface coextensive with one wafer surface, and a second wall located at the opposite side of the wafer and having an expansive surface coextensive with the other wafer surface. The first wall and wafer thus define a first chamber, and the second wall and wafer define a second chamber in communication with the first chamber at the periphery of the wafer. A housing that carries the wafers and walls directs air from the exterior of the canister into the first chamber, past one side of the wafer and its periphery and into the second chamber, past the opposite side of the wafer and thereafter to the interior of the canister, for imparting heat to the adsorbent material contained therein. The arrangement is characterized by both high efficiency and low cost.