A convection oven comprising: a housing having an oven cavity and an oven door (15a, 15b) for access to the oven cavity; a left side air channel (26a-29a) located on a left side cavity wall of the oven cavity; a right side air channel (26b-29b) located on a right side cavity wall of the oven cavity; an air blower for sending heated air to the left side air channel and the right side air channel; and an intermediate air plenum (127, 128) defining the bottom of an upper cooking chamber and the top of a lower cooking chamber within the oven cavity, the intermediate air plenum comprising: a left side air inlet (127a, 128a) configured to receive a portion of the heated air from the left side air channel; a right side air inlet (127b, 128b) configured to receive a portion of the heated air from the right side air channel; a top plenum surface (127c, 128c) defining the top of the interior space of the intermediate air plenum and including a plurality of top air outlets (127e, 128e), the top air outlets being configured to direct a portion of the heated air received through the left side air inlet and the right side air inlet upwards into the upper cooking chamber; and a bottom plenum surface (127d, 128d) defining the bottom of the interior space of the intermediate air plenum and including a plurality of bottom air outlets (127f, 128f) the bottom air outlets being configured to direct a portion of the heated air received through the left side air inlet and the right side air inlet downwards into the lower cooking chamber; wherein at least one of the top plenum surface and the bottom plenum surface is curved. a housing having an oven cavity and an oven door (15a, 15b) for access to the oven cavity; a left side air channel (26a-29a) located on a left side cavity wall of the oven cavity; a right side air channel (26b-29b) located on a right side cavity wall of the oven cavity; an air blower for sending heated air to the left side air channel and the right side air channel; and an intermediate air plenum (127, 128) defining the bottom of an upper cooking chamber and the top of a lower cooking chamber within the oven cavity, the intermediate air plenum comprising: a left side air inlet (127a, 128a) configured to receive a portion of the heated air from the left side air channel; a right side air inlet (127b, 128b) configured to receive a portion of the heated air from the right side air channel; a top plenum surface (127c, 128c) defining the top of the interior space of the intermediate air plenum and including a plurality of top air outlets (127e, 128e), the top air outlets being configured to direct a portion of the heated air received through the left side air inlet and the right side air inlet upwards into the upper cooking chamber; and a bottom plenum surface (127d, 128d) defining the bottom of the interior space of the intermediate air plenum and including a plurality of bottom air outlets (127f, 128f) the bottom air outlets being configured to direct a portion of the heated air received through the left side air inlet and the right side air inlet downwards into the lower cooking chamber; wherein at least one of the top plenum surface and the bottom plenum surface is curved. a left side air inlet (127a, 128a) configured to receive a portion of the heated air from the left side air channel; a right side air inlet (127b, 128b) configured to receive a portion of the heated air from the right side air channel; a top plenum surface (127c, 128c) defining the top of the interior space of the intermediate air plenum and including a plurality of top air outlets (127e, 128e), the top air outlets being configured to direct a portion of the heated air received through the left side air inlet and the right side air inlet upwards into the upper cooking chamber; and a bottom plenum surface (127d, 128d) defining the bottom of the interior space of the intermediate air plenum and including a plurality of bottom air outlets (127f, 128f) the bottom air outlets being configured to direct a portion of the heated air received through the left side air inlet and the right side air inlet downwards into the lower cooking chamber; wherein at least one of the top plenum surface and the bottom plenum surface is curved.