Abstract: A combination oven for the preparation of food has a cooking chamber containing heating elements, a fan and an atomizer for radiant, convective or steam cooking. The humidity within the cooking chamber is controlled by a water valve and either by forcing dry air into the cooking chamber and venting the humid air or by using a pressure box. Without any moving parts, the pressure box controls air exchange of the cooking chamber according to the level of water within the pressure box and the pressure in the cooking chamber. The oven has a condensate tank to collect condensation drained from the cooking chamber. The pressure box and condensate tanks form water barriers effectively isolating the cooking chamber from the vent and drain during cooking until venting is required.