A method of recycling waste treatment air used in a downstream oven zone of an oven for creating a preheating air to preheating a product in process prior to entering the downstream oven zone comprising the steps of: introducing a treatment air having a treatment air temperature and a treatment air dew point temperature through a zone inlet in at least one downstream oven zone for treating the product in process; exhausting a waste treatment air through an oven duct assembly secured to a zone outlet in the at least one downstream oven zone following the treatment of a product in process and recycling at least a first portion of the waste treatment air from the zone outlet to the zone inlet of the at least one downstream oven zone and conditioning the waste treatment air for creating new treatment air to treat additional product in process; transferring a second portion of the waste treatment air through a transfer duct extending between the oven duct assembly and a preheating zone; creating a preheating air having a preheating air temperature and a preheating air dew point temperature from the second portion of the waste treatment air transferred to the preheating zone to preheat additional product in process; introducing the preheating air into the preheating zone through a preheating inlet to preheat additional product in process. Characterized in that the method further includes the step of conditioning the waste treatment air in the oven duct assembly for creating new treatment air having the treatment air temperature and the treatment air dew point temperature to treat additional product in process and wherein conditioning includes either the step of heating the waste treatment air with an oven heat source to condition the waste treatment air and create the new treatment air prior to entering the at least one oven zone to treat additional product in process or the step of introducing ambient air to the waste treatment air to condition the waste treatment air and create the new treatment air prior to entering the at least one oven zone to treat additional product in process; wherein the introducing the preheating air step is further defined as introducing the preheating air into the preheating zone through the preheating inlet to preheat the product in process to a product temperature being at least equal to the treatment air dew point temperature for eliminating surface condensation on the product in process during the introducing treatment air step; and wherein the product-in-process is a food product. introducing a treatment air having a treatment air temperature and a treatment air dew point temperature through a zone inlet in at least one downstream oven zone for treating the product in process; exhausting a waste treatment air through an oven duct assembly secured to a zone outlet in the at least one downstream oven zone following the treatment of a product in process and recycling at least a first portion of the waste treatment air from the zone outlet to the zone inlet of the at least one downstream oven zone and conditioning the waste treatment air for creating new treatment air to treat additional product in process; transferring a second portion of the waste treatment air through a transfer duct extending between the oven duct assembly and a preheating zone; creating a preheating air having a preheating air temperature and a preheating air dew point temperature from the second portion of the waste treatment air transferred to the preheating zone to preheat additional product in process; introducing the preheating air into the preheating zone through a preheating inlet to preheat additional product in process.